[Note: This question had the original title "C (ish) style union in C#"
but as Jeff's comment informed me, apparently this structure is called a 'discriminated union']
Excuse the verbosity of this question.
There are a couple of similar sounding questions to mine already in SO but they seem to concentrate on the memory saving benefits of the union or using it for interop.
Here is an example of such a question.
My desire to have a union type thing is somewhat different.
I am writing some code at the moment which generates objects that look a bit like this
public class ValueWrapper
{
public DateTime ValueCreationDate;
// ... other meta data about the value
public object ValueA;
public object ValueB;
}
Pretty complicated stuff I think you will agree. The thing is that ValueA can only be of a few certain types (let's say string, int and Foo (which is a class) and ValueB can be another small set of types. I don't like treating these values as objects (I want the warm snugly feeling of coding with a bit of type safety).
So I thought about writing a trivial little wrapper class to express the fact that ValueA logically is a reference to a particular type. I called the class Union because what I am trying to achieve reminded me of the union concept in C.
public class Union<A, B, C>
{
private readonly Type type;
public readonly A a;
public readonly B b;
public readonly C c;
public A A{get {return a;}}
public B B{get {return b;}}
public C C{get {return c;}}
public Union(A a)
{
type = typeof(A);
this.a = a;
}
public Union(B b)
{
type = typeof(B);
this.b = b;
}
public Union(C c)
{
type = typeof(C);
this.c = c;
}
/// <summary>
/// Returns true if the union contains a value of type T
/// </summary>
/// <remarks>The type of T must exactly match the type</remarks>
public bool Is<T>()
{
return typeof(T) == type;
}
/// <summary>
/// Returns the union value cast to the given type.
/// </summary>
/// <remarks>If the type of T does not exactly match either X or Y, then the value <c>default(T)</c> is returned.</remarks>
public T As<T>()
{
if(Is<A>())
{
return (T)(object)a; // Is this boxing and unboxing unavoidable if I want the union to hold value types and reference types?
//return (T)x; // This will not compile: Error = "Cannot cast expression of type 'X' to 'T'."
}
if(Is<B>())
{
return (T)(object)b;
}
if(Is<C>())
{
return (T)(object)c;
}
return default(T);
}
}
Using this class ValueWrapper now looks like this
public class ValueWrapper2
{
public DateTime ValueCreationDate;
public Union<int, string, Foo> ValueA;
public Union<double, Bar, Foo> ValueB;
}
which is something like what I wanted to achieve but I am missing one fairly crucial element - that is compiler enforced type checking when calling the Is and As functions as the following code demonstrates
public void DoSomething()
{
if(ValueA.Is<string>())
{
var s = ValueA.As<string>();
// .... do somethng
}
if(ValueA.Is<char>()) // I would really like this to be a compile error
{
char c = ValueA.As<char>();
}
}
IMO It is not valid to ask ValueA if it is a char since its definition clearly says it is not - this is a programming error and I would like the compiler to pick up on this. [Also if I could get this correct then (hopefully) I would get intellisense too - which would be a boon.]
In order to achieve this I would want to tell the compiler that the type T can be one of A, B or C
public bool Is<T>() where T : A
or T : B // Yes I know this is not legal!
or T : C
{
return typeof(T) == type;
}
Does anyone have any idea if what I want to achieve is possible? Or am I just plain stupid for writing this class in the first place?
I don't really like the type-checking and type-casting solutions provided above, so here's 100% type-safe union which will throw compilation errors if you attempt to use the wrong datatype:
using System;
namespace Juliet
{
class Program
{
static void Main(string[] args)
{
Union3<int, char, string>[] unions = new Union3<int,char,string>[]
{
new Union3<int, char, string>.Case1(5),
new Union3<int, char, string>.Case2('x'),
new Union3<int, char, string>.Case3("Juliet")
};
foreach (Union3<int, char, string> union in unions)
{
string value = union.Match(
num => num.ToString(),
character => new string(new char[] { character }),
word => word);
Console.WriteLine("Matched union with value '{0}'", value);
}
Console.ReadLine();
}
}
public abstract class Union3<A, B, C>
{
public abstract T Match<T>(Func<A, T> f, Func<B, T> g, Func<C, T> h);
// private ctor ensures no external classes can inherit
private Union3() { }
public sealed class Case1 : Union3<A, B, C>
{
public readonly A Item;
public Case1(A item) : base() { this.Item = item; }
public override T Match<T>(Func<A, T> f, Func<B, T> g, Func<C, T> h)
{
return f(Item);
}
}
public sealed class Case2 : Union3<A, B, C>
{
public readonly B Item;
public Case2(B item) { this.Item = item; }
public override T Match<T>(Func<A, T> f, Func<B, T> g, Func<C, T> h)
{
return g(Item);
}
}
public sealed class Case3 : Union3<A, B, C>
{
public readonly C Item;
public Case3(C item) { this.Item = item; }
public override T Match<T>(Func<A, T> f, Func<B, T> g, Func<C, T> h)
{
return h(Item);
}
}
}
}
I like the direction of the accepted solution but it doesn't scale well for unions of more than three items (e.g. a union of 9 items would require 9 class definitions).
Here is another approach that is also 100% type-safe at compile-time, but that is easy to grow to large unions.
public class UnionBase<A>
{
dynamic value;
public UnionBase(A a) { value = a; }
protected UnionBase(object x) { value = x; }
protected T InternalMatch<T>(params Delegate[] ds)
{
var vt = value.GetType();
foreach (var d in ds)
{
var mi = d.Method;
// These are always true if InternalMatch is used correctly.
Debug.Assert(mi.GetParameters().Length == 1);
Debug.Assert(typeof(T).IsAssignableFrom(mi.ReturnType));
var pt = mi.GetParameters()[0].ParameterType;
if (pt.IsAssignableFrom(vt))
return (T)mi.Invoke(null, new object[] { value });
}
throw new Exception("No appropriate matching function was provided");
}
public T Match<T>(Func<A, T> fa) { return InternalMatch<T>(fa); }
}
public class Union<A, B> : UnionBase<A>
{
public Union(A a) : base(a) { }
public Union(B b) : base(b) { }
protected Union(object x) : base(x) { }
public T Match<T>(Func<A, T> fa, Func<B, T> fb) { return InternalMatch<T>(fa, fb); }
}
public class Union<A, B, C> : Union<A, B>
{
public Union(A a) : base(a) { }
public Union(B b) : base(b) { }
public Union(C c) : base(c) { }
protected Union(object x) : base(x) { }
public T Match<T>(Func<A, T> fa, Func<B, T> fb, Func<C, T> fc) { return InternalMatch<T>(fa, fb, fc); }
}
public class Union<A, B, C, D> : Union<A, B, C>
{
public Union(A a) : base(a) { }
public Union(B b) : base(b) { }
public Union(C c) : base(c) { }
public Union(D d) : base(d) { }
protected Union(object x) : base(x) { }
public T Match<T>(Func<A, T> fa, Func<B, T> fb, Func<C, T> fc, Func<D, T> fd) { return InternalMatch<T>(fa, fb, fc, fd); }
}
public class Union<A, B, C, D, E> : Union<A, B, C, D>
{
public Union(A a) : base(a) { }
public Union(B b) : base(b) { }
public Union(C c) : base(c) { }
public Union(D d) : base(d) { }
public Union(E e) : base(e) { }
protected Union(object x) : base(x) { }
public T Match<T>(Func<A, T> fa, Func<B, T> fb, Func<C, T> fc, Func<D, T> fd, Func<E, T> fe) { return InternalMatch<T>(fa, fb, fc, fd, fe); }
}
public class DiscriminatedUnionTest : IExample
{
public Union<int, bool, string, int[]> MakeUnion(int n)
{
return new Union<int, bool, string, int[]>(n);
}
public Union<int, bool, string, int[]> MakeUnion(bool b)
{
return new Union<int, bool, string, int[]>(b);
}
public Union<int, bool, string, int[]> MakeUnion(string s)
{
return new Union<int, bool, string, int[]>(s);
}
public Union<int, bool, string, int[]> MakeUnion(params int[] xs)
{
return new Union<int, bool, string, int[]>(xs);
}
public void Print(Union<int, bool, string, int[]> union)
{
var text = union.Match(
n => "This is an int " + n.ToString(),
b => "This is a boolean " + b.ToString(),
s => "This is a string" + s,
xs => "This is an array of ints " + String.Join(", ", xs));
Console.WriteLine(text);
}
public void Run()
{
Print(MakeUnion(1));
Print(MakeUnion(true));
Print(MakeUnion("forty-two"));
Print(MakeUnion(0, 1, 1, 2, 3, 5, 8));
}
}
I wrote some blog posts on this subject that might be useful:
Union Types in C#
Implementing Tic-Tac-Toe Using State Classes
Let's say you have a shopping cart scenario with three states: "Empty", "Active" and "Paid", each with different behavior.
You create have a ICartState interface that all states have in common (and it could just be an empty marker interface)
You create three classes that implement that interface. (The classes do not have to be in an inheritance relationship)
The interface contains a "fold" method, whereby you pass a lambda in for each state or case that you need to handle.
You could use the F# runtime from C# but as a lighter weight alternative, I have written a little T4 template for generating code like this.
Here's the interface:
partial interface ICartState
{
ICartState Transition(
Func<CartStateEmpty, ICartState> cartStateEmpty,
Func<CartStateActive, ICartState> cartStateActive,
Func<CartStatePaid, ICartState> cartStatePaid
);
}
And here's the implementation:
class CartStateEmpty : ICartState
{
ICartState ICartState.Transition(
Func<CartStateEmpty, ICartState> cartStateEmpty,
Func<CartStateActive, ICartState> cartStateActive,
Func<CartStatePaid, ICartState> cartStatePaid
)
{
// I'm the empty state, so invoke cartStateEmpty
return cartStateEmpty(this);
}
}
class CartStateActive : ICartState
{
ICartState ICartState.Transition(
Func<CartStateEmpty, ICartState> cartStateEmpty,
Func<CartStateActive, ICartState> cartStateActive,
Func<CartStatePaid, ICartState> cartStatePaid
)
{
// I'm the active state, so invoke cartStateActive
return cartStateActive(this);
}
}
class CartStatePaid : ICartState
{
ICartState ICartState.Transition(
Func<CartStateEmpty, ICartState> cartStateEmpty,
Func<CartStateActive, ICartState> cartStateActive,
Func<CartStatePaid, ICartState> cartStatePaid
)
{
// I'm the paid state, so invoke cartStatePaid
return cartStatePaid(this);
}
}
Now let's say you extend the CartStateEmpty and CartStateActive with an AddItem method which is not implemented by CartStatePaid.
And also let's say that CartStateActive has a Pay method that the other states dont have.
Then here's some code that shows it in use -- adding two items and then paying for the cart:
public ICartState AddProduct(ICartState currentState, Product product)
{
return currentState.Transition(
cartStateEmpty => cartStateEmpty.AddItem(product),
cartStateActive => cartStateActive.AddItem(product),
cartStatePaid => cartStatePaid // not allowed in this case
);
}
public void Example()
{
var currentState = new CartStateEmpty() as ICartState;
//add some products
currentState = AddProduct(currentState, Product.ProductX);
currentState = AddProduct(currentState, Product.ProductY);
//pay
const decimal paidAmount = 12.34m;
currentState = currentState.Transition(
cartStateEmpty => cartStateEmpty, // not allowed in this case
cartStateActive => cartStateActive.Pay(paidAmount),
cartStatePaid => cartStatePaid // not allowed in this case
);
}
Note that this code is completely typesafe -- no casting or conditionals anywhere, and compiler errors if you try to pay for an empty cart, say.
I have written a library for doing this at https://github.com/mcintyre321/OneOf
Install-Package OneOf
It has the generic types in it for doing DUs e.g. OneOf<T0, T1> all the way to
OneOf<T0, ..., T9>. Each of those has a .Match, and a .Switch statement which you can use for compiler safe typed behaviour, e.g.:
```
OneOf<string, ColorName, Color> backgroundColor = getBackground();
Color c = backgroundColor.Match(
str => CssHelper.GetColorFromString(str),
name => new Color(name),
col => col
);
```
I am not sure I fully understand your goal. In C, a union is a structure that uses the same memory locations for more than one field. For example:
typedef union
{
float real;
int scalar;
} floatOrScalar;
The floatOrScalar union could be used as a float, or an int, but they both consume the same memory space. Changing one changes the other. You can achieve the same thing with a struct in C#:
[StructLayout(LayoutKind.Explicit)]
struct FloatOrScalar
{
[FieldOffset(0)]
public float Real;
[FieldOffset(0)]
public int Scalar;
}
The above structure uses 32bits total, rather than 64bits. This is only possible with a struct. Your example above is a class, and given the nature of the CLR, makes no guarantee about memory efficiency. If you change a Union<A, B, C> from one type to another, you are not necessarily reusing memory...most likely, you are allocating a new type on the heap and dropping a different pointer in the backing object field. Contrary to a real union, your approach may actually cause more heap thrashing than you would otherwise get if you did not use your Union type.
char foo = 'B';
bool bar = foo is int;
This results in a warning, not an error. If you're looking for your Is and As functions to be analogs for the C# operators, then you shouldn't be restricting them in that way anyhow.
If you allow multiple types, you cannot achieve type safety (unless the types are related).
You can't and won't achieve any kind of type safety, you could only achieve byte-value-safety using FieldOffset.
It would make much more sense to have a generic ValueWrapper<T1, T2> with T1 ValueA and T2 ValueB, ...
P.S.: when talking about type-safety I mean compile-time type-safety.
If you need a code wrapper (performing bussiness logic on modifications you can use something along the lines of:
public class Wrapper
{
public ValueHolder<int> v1 = 5;
public ValueHolder<byte> v2 = 8;
}
public struct ValueHolder<T>
where T : struct
{
private T value;
public ValueHolder(T value) { this.value = value; }
public static implicit operator T(ValueHolder<T> valueHolder) { return valueHolder.value; }
public static implicit operator ValueHolder<T>(T value) { return new ValueHolder<T>(value); }
}
For an easy way out you could use (it has performance issues, but it is very simple):
public class Wrapper
{
private object v1;
private object v2;
public T GetValue1<T>() { if (v1.GetType() != typeof(T)) throw new InvalidCastException(); return (T)v1; }
public void SetValue1<T>(T value) { v1 = value; }
public T GetValue2<T>() { if (v2.GetType() != typeof(T)) throw new InvalidCastException(); return (T)v2; }
public void SetValue2<T>(T value) { v2 = value; }
}
//usage:
Wrapper wrapper = new Wrapper();
wrapper.SetValue1("aaaa");
wrapper.SetValue2(456);
string s = wrapper.GetValue1<string>();
DateTime dt = wrapper.GetValue1<DateTime>();//InvalidCastException
Here is my attempt. It does compile time checking of types, using generic type constraints.
class Union {
public interface AllowedType<T> { };
internal object val;
internal System.Type type;
}
static class UnionEx {
public static T As<U,T>(this U x) where U : Union, Union.AllowedType<T> {
return x.type == typeof(T) ?(T)x.val : default(T);
}
public static void Set<U,T>(this U x, T newval) where U : Union, Union.AllowedType<T> {
x.val = newval;
x.type = typeof(T);
}
public static bool Is<U,T>(this U x) where U : Union, Union.AllowedType<T> {
return x.type == typeof(T);
}
}
class MyType : Union, Union.AllowedType<int>, Union.AllowedType<string> {}
class TestIt
{
static void Main()
{
MyType bla = new MyType();
bla.Set(234);
System.Console.WriteLine(bla.As<MyType,int>());
System.Console.WriteLine(bla.Is<MyType,string>());
System.Console.WriteLine(bla.Is<MyType,int>());
bla.Set("test");
System.Console.WriteLine(bla.As<MyType,string>());
System.Console.WriteLine(bla.Is<MyType,string>());
System.Console.WriteLine(bla.Is<MyType,int>());
// compile time errors!
// bla.Set('a');
// bla.Is<MyType,char>()
}
}
It could use some prettying-up. Especially, I couldn't figure out how to get rid of the type parameters to As/Is/Set (isn't there a way to specify one type parameter and let C# figure the other one?)
So I've hit this same problem many times, and I just came up with a solution that gets the syntax I want (at the expense of some ugliness in the implementation of the Union type.)
To recap: we want this sort of usage at the call site.
Union<int, string> u;
u = 1492;
int yearColumbusDiscoveredAmerica = u;
u = "hello world";
string traditionalGreeting = u;
var answers = new SortedList<string, Union<int, string, DateTime>>();
answers["life, the universe, and everything"] = 42;
answers["D-Day"] = new DateTime(1944, 6, 6);
answers["C#"] = "is awesome";
We want the following examples to fail to compile, however, so that we get a modicum of type safety.
DateTime dateTimeColumbusDiscoveredAmerica = u;
Foo fooInstance = u;
For extra credit, let's also not take up more space than absolutely needed.
With all that said, here's my implementation for two generic type parameters. The implementation for three, four, and so on type parameters is straight-forward.
public abstract class Union<T1, T2>
{
public abstract int TypeSlot
{
get;
}
public virtual T1 AsT1()
{
throw new TypeAccessException(string.Format(
"Cannot treat this instance as a {0} instance.", typeof(T1).Name));
}
public virtual T2 AsT2()
{
throw new TypeAccessException(string.Format(
"Cannot treat this instance as a {0} instance.", typeof(T2).Name));
}
public static implicit operator Union<T1, T2>(T1 data)
{
return new FromT1(data);
}
public static implicit operator Union<T1, T2>(T2 data)
{
return new FromT2(data);
}
public static implicit operator Union<T1, T2>(Tuple<T1, T2> data)
{
return new FromTuple(data);
}
public static implicit operator T1(Union<T1, T2> source)
{
return source.AsT1();
}
public static implicit operator T2(Union<T1, T2> source)
{
return source.AsT2();
}
private class FromT1 : Union<T1, T2>
{
private readonly T1 data;
public FromT1(T1 data)
{
this.data = data;
}
public override int TypeSlot
{
get { return 1; }
}
public override T1 AsT1()
{
return this.data;
}
public override string ToString()
{
return this.data.ToString();
}
public override int GetHashCode()
{
return this.data.GetHashCode();
}
}
private class FromT2 : Union<T1, T2>
{
private readonly T2 data;
public FromT2(T2 data)
{
this.data = data;
}
public override int TypeSlot
{
get { return 2; }
}
public override T2 AsT2()
{
return this.data;
}
public override string ToString()
{
return this.data.ToString();
}
public override int GetHashCode()
{
return this.data.GetHashCode();
}
}
private class FromTuple : Union<T1, T2>
{
private readonly Tuple<T1, T2> data;
public FromTuple(Tuple<T1, T2> data)
{
this.data = data;
}
public override int TypeSlot
{
get { return 0; }
}
public override T1 AsT1()
{
return this.data.Item1;
}
public override T2 AsT2()
{
return this.data.Item2;
}
public override string ToString()
{
return this.data.ToString();
}
public override int GetHashCode()
{
return this.data.GetHashCode();
}
}
}
And my attempt on minimal yet extensible solution using nesting of Union/Either type.
Also usage of default parameters in Match method naturally enables "Either X Or Default" scenario.
using System;
using System.Reflection;
using NUnit.Framework;
namespace Playground
{
[TestFixture]
public class EitherTests
{
[Test]
public void Test_Either_of_Property_or_FieldInfo()
{
var some = new Some(false);
var field = some.GetType().GetField("X");
var property = some.GetType().GetProperty("Y");
Assert.NotNull(field);
Assert.NotNull(property);
var info = Either<PropertyInfo, FieldInfo>.Of(field);
var infoType = info.Match(p => p.PropertyType, f => f.FieldType);
Assert.That(infoType, Is.EqualTo(typeof(bool)));
}
[Test]
public void Either_of_three_cases_using_nesting()
{
var some = new Some(false);
var field = some.GetType().GetField("X");
var parameter = some.GetType().GetConstructors()[0].GetParameters()[0];
Assert.NotNull(field);
Assert.NotNull(parameter);
var info = Either<ParameterInfo, Either<PropertyInfo, FieldInfo>>.Of(parameter);
var name = info.Match(_ => _.Name, _ => _.Name, _ => _.Name);
Assert.That(name, Is.EqualTo("a"));
}
public class Some
{
public bool X;
public string Y { get; set; }
public Some(bool a)
{
X = a;
}
}
}
public static class Either
{
public static T Match<A, B, C, T>(
this Either<A, Either<B, C>> source,
Func<A, T> a = null, Func<B, T> b = null, Func<C, T> c = null)
{
return source.Match(a, bc => bc.Match(b, c));
}
}
public abstract class Either<A, B>
{
public static Either<A, B> Of(A a)
{
return new CaseA(a);
}
public static Either<A, B> Of(B b)
{
return new CaseB(b);
}
public abstract T Match<T>(Func<A, T> a = null, Func<B, T> b = null);
private sealed class CaseA : Either<A, B>
{
private readonly A _item;
public CaseA(A item) { _item = item; }
public override T Match<T>(Func<A, T> a = null, Func<B, T> b = null)
{
return a == null ? default(T) : a(_item);
}
}
private sealed class CaseB : Either<A, B>
{
private readonly B _item;
public CaseB(B item) { _item = item; }
public override T Match<T>(Func<A, T> a = null, Func<B, T> b = null)
{
return b == null ? default(T) : b(_item);
}
}
}
}
You could throw exceptions once there's an attempt to access variables that haven't been initialized, ie if it's created with an A parameter and later on there's an attempt to access B or C, it could throw, say, UnsupportedOperationException. You'd need a getter to make it work though.
The C# Language Design Team discussed discriminated unions in January 2017 https://github.com/dotnet/csharplang/blob/master/meetings/2017/LDM-2017-01-10.md#discriminated-unions-via-closed-types
You can vote for the feature request at https://github.com/dotnet/csharplang/issues/113
You can export a pseudo-pattern matching function, like I use for the Either type in my Sasa library. There's currently runtime overhead, but I eventually plan to add a CIL analysis to inline all the delegates into a true case statement.
It's not possible to do with exactly the syntax you've used but with a bit more verbosity and copy/paste it's easy to make overload resolution do the job for you:
// this code is ok
var u = new Union("");
if (u.Value(Is.OfType()))
{
u.Value(Get.ForType());
}
// and this one will not compile
if (u.Value(Is.OfType()))
{
u.Value(Get.ForType());
}
By now it should be pretty obvious how to implement it:
public class Union
{
private readonly Type type;
public readonly A a;
public readonly B b;
public readonly C c;
public Union(A a)
{
type = typeof(A);
this.a = a;
}
public Union(B b)
{
type = typeof(B);
this.b = b;
}
public Union(C c)
{
type = typeof(C);
this.c = c;
}
public bool Value(TypeTestSelector _)
{
return typeof(A) == type;
}
public bool Value(TypeTestSelector _)
{
return typeof(B) == type;
}
public bool Value(TypeTestSelector _)
{
return typeof(C) == type;
}
public A Value(GetValueTypeSelector _)
{
return a;
}
public B Value(GetValueTypeSelector _)
{
return b;
}
public C Value(GetValueTypeSelector _)
{
return c;
}
}
public static class Is
{
public static TypeTestSelector OfType()
{
return null;
}
}
public class TypeTestSelector
{
}
public static class Get
{
public static GetValueTypeSelector ForType()
{
return null;
}
}
public class GetValueTypeSelector
{
}
There are no checks for extracting the value of the wrong type, e.g.:
var u = Union(10);
string s = u.Value(Get.ForType());
So you might consider adding necessary checks and throw exceptions in such cases.
I am currently trying to create a Julia Runtime in .NET. Julia has types like Union{Int, String}... Etc. I am currently trying to simulate this .NET (without doing weird IL that would not be able to be called from c#).
Here is a compile time implementation of a union of structures. I will be creating more unions for object unions, and cross object and struct unions (this will be the most complex case).
public struct Union<T1,T2> where T1 : struct where T2 : struct{
private byte type;
[FieldOffset(1)] private T1 a1;
[FieldOffset(1)] private T2 a2;
public T1 A1 {
get => a1;
set {
a1 = value;
type = 1;
}
}
public T2 A2 {
get => a2;
set {
a2 = value;
type = 2;
}
}
public Union(int _ = 0) {
type = 0;
a1 = default;
a2 = default;
}
public Union(T1 a) : this() => A1 = a;
public Union(T2 a) : this() => A2 = a;
public bool HasValue => type < 1 || type > 2;
public bool IsNull => !HasValue;
public bool IsT1 => type == 1;
public bool IsT2 => type == 2;
public Type GetType() {
switch (type) {
case 1: return typeof(T1);
case 2: return typeof(T2);
default: return null;
}
}
}
You can use the above like the following:
Union<int, long> myUnion(5); \\Set int inside
myUnion.a2 = 5;
Type theTypeInside = myUnion.GetType(); //long
myUnion.a1 = 5;
theTypeInside = myUnion.GetType(); //int
I will also be creating dynamic union generators or aligned unions for the cross object and struct union.
Take a look at:Generated Struct Union Output to see the current compile time unions I am using.
If you want to create a union of any size take a look at Generator for Struct Unions
If anyone has any improvements for the above let me know! Implementing julia into .NET is an extraordinarily hard task!
I use own of Union Type.
Consider an example to make it clearer.
Imagine we have Contact class:
public class Contact
{
public string Name { get; set; }
public string EmailAddress { get; set; }
public string PostalAdrress { get; set; }
}
These are all defined as simple strings, but really are they just strings?
Of course not. The Name can consist of First Name and Last Name. Or is an Email just a set of symbols? I know that at least it should contain # and it is necessarily.
Let's improve us domain model
public class PersonalName
{
public PersonalName(string firstName, string lastName) { ... }
public string Name() { return _fistName + " " _lastName; }
}
public class EmailAddress
{
public EmailAddress(string email) { ... }
}
public class PostalAdrress
{
public PostalAdrress(string address, string city, int zip) { ... }
}
In this classes will be validations during creating and we will eventually have valid models. Consturctor in PersonaName class require FirstName and LastName at the same time. This means that after the creation, it can not have invalid state.
And contact class respectively
public class Contact
{
public PersonalName Name { get; set; }
public EmailAdress EmailAddress { get; set; }
public PostalAddress PostalAddress { get; set; }
}
In this case we have same problem, object of Contact class may be in invalid state. I mean it may have EmailAddress but haven't Name
var contact = new Contact { EmailAddress = new EmailAddress("foo#bar.com") };
Let's fix it and create Contact class with constructor which requires PersonalName, EmailAddress and PostalAddress:
public class Contact
{
public Contact(
PersonalName personalName,
EmailAddress emailAddress,
PostalAddress postalAddress
)
{
...
}
}
But here we have another problem. What if Person have only EmailAdress and haven't PostalAddress?
If we think about it there we realize that there are three possibilities of valid state of Contact class object:
A contact only has an email address
A contact only has a postal address
A contact has both an email address and a postal address
Let's write out domain models. For the beginning we will create Contact Info class which state will be corresponding with above cases.
public class ContactInfo
{
public ContactInfo(EmailAddress emailAddress) { ... }
public ContactInfo(PostalAddress postalAddress) { ... }
public ContactInfo(Tuple<EmailAddress,PostalAddress> emailAndPostalAddress) { ... }
}
And Contact class:
public class Contact
{
public Contact(
PersonalName personalName,
ContactInfo contactInfo
)
{
...
}
}
Let's try use it:
var contact = new Contact(
new PersonalName("James", "Bond"),
new ContactInfo(
new EmailAddress("agent#007.com")
)
);
Console.WriteLine(contact.PersonalName()); // James Bond
Console.WriteLine(contact.ContactInfo().???) // here we have problem, because ContactInfo have three possible state and if we want print it we would write `if` cases
Let's add Match method in ContactInfo class
public class ContactInfo
{
// constructor
public TResult Match<TResult>(
Func<EmailAddress,TResult> f1,
Func<PostalAddress,TResult> f2,
Func<Tuple<EmailAddress,PostalAddress>> f3
)
{
if (_emailAddress != null)
{
return f1(_emailAddress);
}
else if(_postalAddress != null)
{
...
}
...
}
}
In the match method, we can write this code, because the state of the contact class is controlled with constructors and it may have only one of the possible states.
Let's create an auxiliary class, so that each time do not write as many code.
public abstract class Union<T1,T2,T3>
where T1 : class
where T2 : class
where T3 : class
{
private readonly T1 _t1;
private readonly T2 _t2;
private readonly T3 _t3;
public Union(T1 t1) { _t1 = t1; }
public Union(T2 t2) { _t2 = t2; }
public Union(T3 t3) { _t3 = t3; }
public TResult Match<TResult>(
Func<T1, TResult> f1,
Func<T2, TResult> f2,
Func<T3, TResult> f3
)
{
if (_t1 != null)
{
return f1(_t1);
}
else if (_t2 != null)
{
return f2(_t2);
}
else if (_t3 != null)
{
return f3(_t3);
}
throw new Exception("can't match");
}
}
We can have such a class in advance for several types, as is done with delegates Func, Action. 4-6 generic type parameters will be in full for Union class.
Let's rewrite ContactInfo class:
public sealed class ContactInfo : Union<
EmailAddress,
PostalAddress,
Tuple<EmaiAddress,PostalAddress>
>
{
public Contact(EmailAddress emailAddress) : base(emailAddress) { }
public Contact(PostalAddress postalAddress) : base(postalAddress) { }
public Contact(Tuple<EmaiAddress, PostalAddress> emailAndPostalAddress) : base(emailAndPostalAddress) { }
}
Here the compiler will ask override for at least one constructor. If we forget to override the rest of the constructors we can't create object of ContactInfo class with another state. This will protect us from runtime exceptions during Matching.
var contact = new Contact(
new PersonalName("James", "Bond"),
new ContactInfo(
new EmailAddress("agent#007.com")
)
);
Console.WriteLine(contact.PersonalName()); // James Bond
Console
.WriteLine(
contact
.ContactInfo()
.Match(
(emailAddress) => emailAddress.Address,
(postalAddress) => postalAddress.City + " " postalAddress.Zip.ToString(),
(emailAndPostalAddress) => emailAndPostalAddress.Item1.Name + emailAndPostalAddress.Item2.City + " " emailAndPostalAddress.Item2.Zip.ToString()
)
);
That's all.
I hope you enjoyed.
Example taken from the site F# for fun and profit
I want to return a Nullable<Value> from a function in a generic class if Value is a value type, and just 'Value' if value is already a reference type.
I've been trying to work with where clauses to achieve this, but I can't seem to use a where class on a non-generic function, even in a generic class.
public class HashTable<Key, Value>
{
private List<ValueSlot> valueSlots = new List<ValueSlot>();
private struct ValueSlot
{
public bool hasValue;
public List<KeyValuePair<Key, Value>> values;
}
//...
public Nullable<Value> TryGetValue(Key key) where Value : struct
{
(bool result, Value value) = TryGetValue(valueSlots, key);
if (result == true)
{
Nullable<Value> myVal = value;
return myVal;
}
else
{
return null;
}
}
public Value TryGetValue(Key key) where Value : class
{
(bool result, Value value) = TryGetValue(valueSlots, key);
return result == true ? value : (Value)null;
}
private (bool, Value) TryGetValue(List<ValueSlot> valueSlots, Key key)
{
//...
}
//...
}
Unfortunately, this doesn't compile an generates a bunch of errors. I would rather not resort to returning tuples out from the class. Is there a simple way to make this approach work that I am missing? I've been trying to get this to work for nearly a week now...
Polymorphism by return type is not supported by C# yet. Generic type constraint is a hint to the compiler and not making method signatures different.
I'd suggest using Maybe<T> so that you can do this:
public class HashTable<Key, Value>
{
public Maybe<Value> TryGetValue(Key key)
{
(bool result, Value value) = TryGetValue(valueSlots, key);
if (result == true)
{
return new Maybe<Value>(value); // or value.ToMaybe() // with the extension method
}
else
{
return Maybe<Value>.Nothing;
}
}
}
This works regardless of what type the Value is.
Here's the implementation that I use:
public static class MaybeEx
{
public static Maybe<T> ToMaybe<T>(this T value)
{
return new Maybe<T>(value);
}
public static T GetValue<T>(this Maybe<T> m, T #default) => m.HasValue ? m.Value : #default;
public static T GetValue<T>(this Maybe<T> m, Func<T> #default) => m.HasValue ? m.Value : #default();
public static Maybe<U> Select<T, U>(this Maybe<T> m, Func<T, U> k)
{
return m.SelectMany(t => k(t).ToMaybe());
}
public static Maybe<U> SelectMany<T, U>(this Maybe<T> m, Func<T, Maybe<U>> k)
{
if (!m.HasValue)
{
return Maybe<U>.Nothing;
}
return k(m.Value);
}
public static Maybe<V> SelectMany<T, U, V>(this Maybe<T> #this, Func<T, Maybe<U>> k, Func<T, U, V> s)
{
return #this.SelectMany(x => k(x).SelectMany(y => s(x, y).ToMaybe()));
}
}
public class Maybe<T>
{
public class MissingValueException : Exception { }
public readonly static Maybe<T> Nothing = new Maybe<T>();
private T _value;
public T Value
{
get
{
if (!this.HasValue)
{
throw new MissingValueException();
}
return _value;
}
private set
{
_value = value;
}
}
public bool HasValue { get; private set; }
public Maybe()
{
HasValue = false;
}
public Maybe(T value)
{
Value = value;
HasValue = true;
}
public T ValueOrDefault(T #default) => this.HasValue ? this.Value : #default;
public T ValueOrDefault(Func<T> #default) => this.HasValue ? this.Value : #default();
public static implicit operator Maybe<T>(T v)
{
return v.ToMaybe();
}
public override string ToString()
{
return this.HasValue ? this.Value.ToString() : "<null>";
}
public override bool Equals(object obj)
{
if (obj is Maybe<T>)
return Equals((Maybe<T>)obj);
return false;
}
public bool Equals(Maybe<T> obj)
{
if (obj == null) return false;
if (!EqualityComparer<T>.Default.Equals(_value, obj._value)) return false;
if (!EqualityComparer<bool>.Default.Equals(this.HasValue, obj.HasValue)) return false;
return true;
}
public override int GetHashCode()
{
int hash = 0;
hash ^= EqualityComparer<T>.Default.GetHashCode(_value);
hash ^= EqualityComparer<bool>.Default.GetHashCode(this.HasValue);
return hash;
}
public static bool operator ==(Maybe<T> left, Maybe<T> right)
{
if (object.ReferenceEquals(left, null))
{
return object.ReferenceEquals(right, null);
}
return left.Equals(right);
}
public static bool operator !=(Maybe<T> left, Maybe<T> right)
{
return !(left == right);
}
}
I believe what you are looking for is a Maybe Monad. It requires some work. But it is worth it imho. Implementation for Maybe Monad for C# is well described here.
You need to make some compromises to make this work:
public V? GetNullable<V>(Key key) where V : struct, Value
{
(bool result, Value value) = TryGetValue(valueSlots, key);
return result ? (V)value : (V?)null;
}
public V GetValueOrNull<V>(Key key) where V : class, Value
{
(bool result, Value value) = TryGetValue(valueSlots, key);
return result == true ? (V)value : null;
}
You must give different names to the two methods, and provide the type as parameter every time you call them:
var h1 = new HashTable<int, DateTime>(); // Value Type
DateTime? date = h1.GetNullable<DateTime>(1);
var h2 = new HashTable<int, Exception>(); // Reference Type
Exception ex = h2.GetValueOrNull<Exception>(1);
I guess that this defeats the purpose though.
With two immutable classes Base and Derived (which derives from Base) I want to define Equality so that
equality is always polymorphic - that is ((Base)derived1).Equals((Base)derived2) will call Derived.Equals
operators == and != will call Equals rather than ReferenceEquals (value equality)
What I did:
class Base: IEquatable<Base> {
public readonly ImmutableType1 X;
readonly ImmutableType2 Y;
public Base(ImmutableType1 X, ImmutableType2 Y) {
this.X = X;
this.Y = Y;
}
public override bool Equals(object obj) {
if (object.ReferenceEquals(this, obj)) return true;
if (obj is null || obj.GetType()!=this.GetType()) return false;
return obj is Base o
&& X.Equals(o.X) && Y.Equals(o.Y);
}
public override int GetHashCode() => HashCode.Combine(X, Y);
// boilerplate
public bool Equals(Base o) => object.Equals(this, o);
public static bool operator ==(Base o1, Base o2) => object.Equals(o1, o2);
public static bool operator !=(Base o1, Base o2) => !object.Equals(o1, o2); }
Here everything ends up in Equals(object) which is always polymorphic so both targets are achieved.
I then derive like this:
class Derived : Base, IEquatable<Derived> {
public readonly ImmutableType3 Z;
readonly ImmutableType4 K;
public Derived(ImmutableType1 X, ImmutableType2 Y, ImmutableType3 Z, ImmutableType4 K) : base(X, Y) {
this.Z = Z;
this.K = K;
}
public override bool Equals(object obj) {
if (object.ReferenceEquals(this, obj)) return true;
if (obj is null || obj.GetType()!=this.GetType()) return false;
return obj is Derived o
&& base.Equals(obj) /* ! */
&& Z.Equals(o.Z) && K.Equals(o.K);
}
public override int GetHashCode() => HashCode.Combine(base.GetHashCode(), Z, K);
// boilerplate
public bool Equals(Derived o) => object.Equals(this, o);
}
Which is basically the same except for one gotcha - when calling base.Equals I call base.Equals(object) and not base.Equals(Derived) (which will cause an endless recursion).
Also Equals(C) will in this implementation do some boxing/unboxing but that is worth it for me.
My questions are -
First is this correct ? my (testing) seems to suggest it is but with C# being so difficult in equality I'm just not sure anymore .. are there any cases where this is wrong ?
and Second - is this good ? are there better cleaner ways to achieve this ?
Well I guess there are two parts to you problem:
executing equals at nested level
restricting to the same type
Would this work? https://dotnetfiddle.net/eVLiMZ
(I had to use some older syntax as it didn't compile in dotnetfiddle otherwise)
using System;
public class Program
{
public class Base
{
public string Name { get; set; }
public string VarName { get; set; }
public override bool Equals(object o)
{
return object.ReferenceEquals(this, o)
|| o.GetType()==this.GetType() && ThisEquals(o);
}
protected virtual bool ThisEquals(object o)
{
Base b = o as Base;
return b != null
&& (Name == b.Name);
}
public override string ToString()
{
return string.Format("[{0}#{1} Name:{2}]", GetType(), VarName, Name);
}
public override int GetHashCode()
{
return Name.GetHashCode();
}
}
public class Derived : Base
{
public int Age { get; set; }
protected override bool ThisEquals(object o)
{
var d = o as Derived;
return base.ThisEquals(o)
&& d != null
&& (d.Age == Age);
}
public override string ToString()
{
return string.Format("[{0}#{1} Name:{2} Age:{3}]", GetType(), VarName, Name, Age);
}
public override int GetHashCode()
{
return base.GetHashCode() ^ Age.GetHashCode();
}
}
public static void Main()
{
var b1 = new Base { Name = "anna", VarName = "b1" };
var b2 = new Base { Name = "leo", VarName = "b2" };
var b3 = new Base { Name = "anna", VarName = "b3" };
var d1 = new Derived { Name = "anna", Age = 21, VarName = "d1" };
var d2 = new Derived { Name = "anna", Age = 12, VarName = "d2" };
var d3 = new Derived { Name = "anna", Age = 21, VarName = "d3" };
var all = new object [] { b1, b2, b3, d1, d2, d3 };
foreach(var a in all)
{
foreach(var b in all)
{
Console.WriteLine("{0}.Equals({1}) => {2}", a, b, a.Equals(b));
}
}
}
}
This method of comparison using Reflection which, other than the extension methods, is simpler. It also keeps private members private.
All of the logic is in the IImmutableExtensions class. It simply looks at what fields are readonly and uses them for the comparison.
You don't need methods in the base or derived classes for the object comparison. Just call the extension method ImmutableEquals when you are overriding ==, !=, and Equals(). Same with the hashcode.
public class Base : IEquatable<Base>, IImmutable
{
public readonly ImmutableType1 X;
readonly ImmutableType2 Y;
public Base(ImmutableType1 X, ImmutableType2 Y) => (this.X, this.Y) = (X, Y);
// boilerplate
public override bool Equals(object obj) => this.ImmutableEquals(obj);
public bool Equals(Base o) => this.ImmutableEquals(o);
public static bool operator ==(Base o1, Base o2) => o1.ImmutableEquals(o2);
public static bool operator !=(Base o1, Base o2) => !o1.ImmutableEquals(o2);
private int? _hashCache;
public override int GetHashCode() => this.ImmutableHash(ref _hashCache);
}
public class Derived : Base, IEquatable<Derived>, IImmutable
{
public readonly ImmutableType3 Z;
readonly ImmutableType4 K;
public Derived(ImmutableType1 X, ImmutableType2 Y, ImmutableType3 Z, ImmutableType4 K) : base(X, Y) => (this.Z, this.K) = (Z, K);
public bool Equals(Derived other) => this.ImmutableEquals(other);
}
And the IImmutableExtensions class:
public static class IImmutableExtensions
{
public static bool ImmutableEquals(this IImmutable o1, object o2)
{
if (ReferenceEquals(o1, o2)) return true;
if (o2 is null || o1.GetType() != o2.GetType() || o1.GetHashCode() != o2.GetHashCode()) return false;
foreach (var tProp in GetImmutableFields(o1))
{
var test = tProp.GetValue(o1)?.Equals(tProp.GetValue(o2));
if (test is null) continue;
if (!test.Value) return false;
}
return true;
}
public static int ImmutableHash(this IImmutable o, ref int? hashCache)
{
if (hashCache is null)
{
hashCache = 0;
foreach (var tProp in GetImmutableFields(o))
{
hashCache = HashCode.Combine(hashCache.Value, tProp.GetValue(o).GetHashCode());
}
}
return hashCache.Value;
}
private static IEnumerable<FieldInfo> GetImmutableFields(object o)
{
var t = o.GetType();
do
{
var fields = t.GetFields(BindingFlags.DeclaredOnly | BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public).Where(field => field.IsInitOnly);
foreach(var field in fields)
{
yield return field;
}
}
while ((t = t.BaseType) != typeof(object));
}
}
Old answer: (I will leave this for reference)
Based on what you were saying about having to cast to object it occurred to me that the methods Equals(object) and Equals(Base) were too ambiguous when calling them from a derived class.
This said to me that the logic should be moved out of both of the classes, to a method that would better describe our intentions.
Equality will remain polymorphic as ImmutableEquals in the base class will call the overridden ValuesEqual. This is where you can decide in each derived class how to compare equality.
This is your code refactored with that goal.
Revised answer:
It occurred to me that all of our logic in IsEqual() and GetHashCode() would work if we simply supplied a tuple that contained the immutable fields that we wanted to compare. This avoids duplicating so much code in every class.
It is up to the developer that creates the derived class to override GetImmutableTuple(). Without using reflection (see other answer), I feel this is the least of all evils.
public class Base : IEquatable<Base>, IImmutable
{
public readonly ImmutableType1 X;
readonly ImmutableType2 Y;
public Base(ImmutableType1 X, ImmutableType2 Y) =>
(this.X, this.Y) = (X, Y);
protected virtual IStructuralEquatable GetImmutableTuple() => (X, Y);
// boilerplate
public override bool Equals(object o) => IsEqual(o as Base);
public bool Equals(Base o) => IsEqual(o);
public static bool operator ==(Base o1, Base o2) => o1.IsEqual(o2);
public static bool operator !=(Base o1, Base o2) => !o1.IsEqual(o2);
public override int GetHashCode() => hashCache is null ? (hashCache = GetImmutableTuple().GetHashCode()).Value : hashCache.Value;
protected bool IsEqual(Base obj) => ReferenceEquals(this, obj) || !(obj is null) && GetType() == obj.GetType() && GetHashCode() == obj.GetHashCode() && GetImmutableTuple() != obj.GetImmutableTuple();
protected int? hashCache;
}
public class Derived : Base, IEquatable<Derived>, IImmutable
{
public readonly ImmutableType3 Z;
readonly ImmutableType4 K;
public Derived(ImmutableType1 X, ImmutableType2 Y, ImmutableType3 Z, ImmutableType4 K) : base(X, Y) =>
(this.Z, this.K) = (Z, K);
protected override IStructuralEquatable GetImmutableTuple() => (base.GetImmutableTuple(), K, Z);
// boilerplate
public bool Equals(Derived o) => IsEqual(o);
}
The code can be simplified using a combination of an extension method and some boilercode. This takes almost all of the pain away and leaves classes focused on comparing their instances without having to deal with all the special edge cases:
namespace System {
public static partial class ExtensionMethods {
public static bool Equals<T>(this T inst, object obj, Func<T, bool> thisEquals) where T : IEquatable<T> =>
object.ReferenceEquals(inst, obj) // same reference -> equal
|| !(obj is null) // this is not null but obj is -> not equal
&& obj.GetType() == inst.GetType() // obj is more derived than this -> not equal
&& obj is T o // obj cannot be cast to this type -> not equal
&& thisEquals(o);
}
}
I can now do:
class Base : IEquatable<Base> {
public SomeType1 X;
SomeType2 Y;
public Base(SomeType1 X, SomeType2 Y) => (this.X, this.Y) = (X, Y);
public bool ThisEquals(Base o) => (X, Y) == (o.X, o.Y);
// boilerplate
public override bool Equals(object obj) => this.Equals(obj, ThisEquals);
public bool Equals(Base o) => object.Equals(this, o);
public static bool operator ==(Base o1, Base o2) => object.Equals(o1, o2);
public static bool operator !=(Base o1, Base o2) => !object.Equals(o1, o2);
}
class Derived : Base, IEquatable<Derived> {
public SomeType3 Z;
SomeType4 K;
public Derived(SomeType1 X, SomeType2 Y, SomeType3 Z, SomeType4 K) : base(X, Y) => (this.Z, this.K) = (Z, K);
public bool ThisEquals(Derived o) => base.ThisEquals(o) && (Z, K) == (o.Z, o.K);
// boilerplate
public override bool Equals(object obj) => this.Equals(obj, ThisEquals);
public bool Equals(Derived o) => object.Equals(this, o);
}
This is good, no casting or null checks and all the real work is clearly separated in ThisEquals.(testing)
For immutable classes it is possible to optimize further by caching the hashcode and using it in Equals to shortcut equality if the hashcodes are different:
namespace System.Immutable {
public interface IImmutableEquatable<T> : IEquatable<T> { };
public static partial class ExtensionMethods {
public static bool ImmutableEquals<T>(this T inst, object obj, Func<T, bool> thisEquals) where T : IImmutableEquatable<T> =>
object.ReferenceEquals(inst, obj) // same reference -> equal
|| !(obj is null) // this is not null but obj is -> not equal
&& obj.GetType() == inst.GetType() // obj is more derived than this -> not equal
&& inst.GetHashCode() == obj.GetHashCode() // optimization, hash codes are different -> not equal
&& obj is T o // obj cannot be cast to this type -> not equal
&& thisEquals(o);
public static int GetHashCode<T>(this T inst, ref int? hashCache, Func<int> thisHashCode) where T : IImmutableEquatable<T> {
if (hashCache is null) hashCache = thisHashCode();
return hashCache.Value;
}
}
}
I can now do:
class Base : IImmutableEquatable<Base> {
public readonly SomeImmutableType1 X;
readonly SomeImmutableType2 Y;
public Base(SomeImmutableType1 X, SomeImmutableType2 Y) => (this.X, this.Y) = (X, Y);
public bool ThisEquals(Base o) => (X, Y) == (o.X, o.Y);
public int ThisHashCode() => (X, Y).GetHashCode();
// boilerplate
public override bool Equals(object obj) => this.ImmutableEquals(obj, ThisEquals);
public bool Equals(Base o) => object.Equals(this, o);
public static bool operator ==(Base o1, Base o2) => object.Equals(o1, o2);
public static bool operator !=(Base o1, Base o2) => !object.Equals(o1, o2);
protected int? hashCache;
public override int GetHashCode() => this.GetHashCode(ref hashCache, ThisHashCode);
}
class Derived : Base, IImmutableEquatable<Derived> {
public readonly SomeImmutableType3 Z;
readonly SomeImmutableType4 K;
public Derived(SomeImmutableType1 X, SomeImmutableType2 Y, SomeImmutableType3 Z, SomeImmutableType4 K) : base(X, Y) => (this.Z, this.K) = (Z, K);
public bool ThisEquals(Derived o) => base.ThisEquals(o) && (Z, K) == (o.Z, o.K);
public new int ThisHashCode() => (base.ThisHashCode(), Z, K).GetHashCode();
// boilerplate
public override bool Equals(object obj) => this.ImmutableEquals(obj, ThisEquals);
public bool Equals(Derived o) => object.Equals(this, o);
public override int GetHashCode() => this.GetHashCode(ref hashCache, ThisHashCode);
}
Which is not too bad - there is more complexity but it is all just boilerplate which I just cut&paste .. the logic is clearly separated in ThisEquals and ThisHashCode
(testing)
Another method would be to use Reflection to automatically compare all of your fields and properties. You just have to decorate them with the Immutable attribute and AutoCompare() will take care of the rest.
This will also use Reflection to build a HashCode based on your fields and properties decorated with Immutable, and then cache it to optimize the object comparison.
public class Base : ComparableImmutable, IEquatable<Base>, IImmutable
{
[Immutable]
public ImmutableType1 X { get; set; }
[Immutable]
readonly ImmutableType2 Y;
public Base(ImmutableType1 X, ImmutableType2 Y) => (this.X, this.Y) = (X, Y);
public bool Equals(Base o) => AutoCompare(o);
}
public class Derived : Base, IEquatable<Derived>, IImmutable
{
[Immutable]
public readonly ImmutableType3 Z;
[Immutable]
readonly ImmutableType4 K;
public Derived(ImmutableType1 X, ImmutableType2 Y, ImmutableType3 Z, ImmutableType4 K)
: base(X, Y)
=> (this.Z, this.K) = (Z, K);
public bool Equals(Derived o) => AutoCompare(o);
}
[AttributeUsage(validOn: AttributeTargets.Field | AttributeTargets.Property)]
public class ImmutableAttribute : Attribute { }
public abstract class ComparableImmutable
{
static BindingFlags flags = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.DeclaredOnly;
protected int? hashCache;
public override int GetHashCode()
{
if (hashCache is null)
{
hashCache = 0;
var type = GetType();
do
{
foreach (var field in type.GetFields(flags).Where(field => Attribute.IsDefined(field, typeof(ImmutableAttribute))))
hashCache = HashCode.Combine(hashCache, field.GetValue(this));
foreach (var property in type.GetProperties(flags).Where(property => Attribute.IsDefined(property, typeof(ImmutableAttribute))))
hashCache = HashCode.Combine(hashCache, property.GetValue(this));
type = type.BaseType;
}
while (type != null);
}
return hashCache.Value;
}
protected bool AutoCompare(object obj2)
{
if (ReferenceEquals(this, obj2)) return true;
if (obj2 is null
|| GetType() != obj2.GetType()
|| GetHashCode() != obj2.GetHashCode())
return false;
var type = GetType();
do
{
foreach (var field in type.GetFields(flags).Where(field => Attribute.IsDefined(field, typeof(ImmutableAttribute))))
{
if (field.GetValue(this) != field.GetValue(obj2))
{
return false;
}
}
foreach (var property in type.GetProperties(flags).Where(property => Attribute.IsDefined(property, typeof(ImmutableAttribute))))
{
if (property.GetValue(this) != property.GetValue(obj2))
{
return false;
}
}
type = type.BaseType;
}
while (type != null);
return true;
}
public override bool Equals(object o) => AutoCompare(o);
public static bool operator ==(Comparable o1, Comparable o2) => o1.AutoCompare(o2);
public static bool operator !=(Comparable o1, Comparable o2) => !o1.AutoCompare(o2);
}