We Keep Coding

Creating public types in AutoFixture 4.8.0 using internal JSON constructors, with many constructor arguments

As at AutoFixture 4.8.0, is there a better alternative to using Fixture.Register to register a function to create a type that exposes only an internal constructor?
In context:
I'm working on a .net standard class library to build API for internal use. We do not want to expose public constructors and as such all constructors for these models are internal. Properties are additionally public readonly. These classes will be instantiated through Json deserialization, and in this particular library there is a model with > 20 properties to consider. As a bonus, we'd like to use [AutoDataAttribute] where possible.
ie. is there an alternative to supplying an internal jsonconstructor with a mixture of non and complex types (also internal) with 20+ arguments using AutoFixture?
[TestFixture]
public sealed class Tests
{
private Fixture _fixture;
[OneTimeSetUp]
public void OneTimeSetup()
{
_fixture = new Fixture();
_fixture.Register(() => new Vehicle(_fixture.Create<string>(), _fixture.Create<int>()));
_fixture.Register(
() => new Driver(_fixture.Create<string>(), _fixture.Create<int>(), _fixture.Create<Vehicle>()));
}
[Test]
public void CanCreateDriverWithVehicle()
{
Func<Driver> func = () => _fixture.Create<Driver>();
func.Should().NotThrow(); // Green
}
}
[PublicAPI]
public sealed class Driver
{
public readonly string Name;
public readonly int Age;
public Vehicle Vehicle;
[JsonConstructor]
internal Driver(string name, int age, Vehicle vehicle)
{
Name = name;
Age = age;
Vehicle = vehicle;
}
}
[PublicAPI]
public sealed class Vehicle
{
public readonly string Manufacturer;
public readonly int Miles;
[JsonConstructor]
internal Vehicle(string manufacturer, int miles)
{
Manufacturer = manufacturer;
Miles = miles;
}
}

By default AutoFixture considers the public constructors only. It doesn't pick up the internal constructors, even if they are accessible from the test execution assembly (not even sure whether there is a reasonable technical possibility to check that).
You can easily customize your fixture to support that. Get inspiration from the following code sample:
[Fact]
public void ShouldActivateTypesWithInternalConstructor()
{
var fixture = new Fixture();
fixture.ResidueCollectors.Add(
new Postprocessor(
new MethodInvoker(
new ModestInternalConstructorQuery()),
new AutoPropertiesCommand()
));
var result = fixture.Create<TypeWithInternalConstructor>();
Assert.NotEqual(0, result.Property);
}
public class ModestInternalConstructorQuery : IMethodQuery
{
public IEnumerable<IMethod> SelectMethods(Type type)
{
if (type == null) throw new ArgumentNullException(nameof(type));
return from ci in type.GetConstructors(BindingFlags.Instance | BindingFlags.NonPublic)
where ci.IsAssembly // Take internal constructors only
let parameters = ci.GetParameters()
where parameters.All(p => p.ParameterType != type)
orderby parameters.Length ascending
select new ConstructorMethod(ci) as IMethod;
}
}
public class TypeWithInternalConstructor
{
public int Property { get; }
internal TypeWithInternalConstructor(int property)
{
Property = property;
}
}

creating custom attribute with logic inside

I have this custom attribute here where it does some logics
[AttributeUsage(AttributeTargets.All)]
public class CustomAttribute : Attribute
{
public CustomAttribute ()
{
bool foo = false;
if (foo)
Console.WriteLine ("TRUE");
}
}
then i want to use it in my component class like this
[Custom]
public class Component
{
public void Test()
{
console.log("test");
}
}
so what i want is every time i created an instance of that component class, it will basically call or execute that code in my attribute to do some logic, but the problem is, it doesn't execute the code inside my custom attribute class. I know I'm doing it wrong, anyone has idea how to do it?

When the class is instantiated, it will not inherently call any code tied to your attribute, or even instantiate it. Attributes are only instantiated when you call them using reflection. If you would want the attributes to be processed when a class is constructed, you would have to call a method in a constructor on your Component class that uses reflection to analyze the attributes on your class.
The ideal approach would be instead to inherit from a base class that has constructor logic:
public class Component : CustomBase
{
public void Test()
{
console.log("test");
}
}
public abstract class CustomBase
{
public CustomBase()
{
bool foo = false;
if (foo)
Console.WriteLine ("TRUE");
}
}

You need to call:
object[] attributes = typeof(MyClass).GetCustomAttributes(true);
somewhere, because this is the code that triggers the attributes constructor to run.
You can make a method in your attribute class, that calls this line, and in your Component, call the attribute method.

As Jason and Cristina said , you need to take account of reflection to code with custom attributes. If you read the code below (from line 18 to 24) you can see some commented out code that list all the CustomAttributes associated with a type.
using System;
using System.Collections.Generic;
using System.ComponentModel.Design;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace CustomAttributeTest
{
class Program
{
static void Main(string[] args)
{
var customCompo = new Component();
customCompo.Test();
//System.Reflection.MemberInfo info = typeof(Component);
//object[] attributes = info.GetCustomAttributes(true);
//for (int i = 0; i < attributes.Length; i++)
//{
// System.Console.WriteLine(attributes[i]);
//}
Console.ReadLine();
}
}
[CustomAttribute(true)]
public class Component
{
public void Test()
{
System.Console.WriteLine("Component contructed");
var member = typeof(Component);
foreach (object attribute in member.GetCustomAttributes(true))
{
if (attribute is CustomAttribute)
{
//noop
}
}
}
}
[AttributeUsage(AttributeTargets.All)]
public class CustomAttribute : Attribute
{
private bool _value;
//this constructor specifes one unnamed argument to the attribute class
public CustomAttribute(bool value)
{
_value = value;
Console.WriteLine(this.ToString());
}
public override string ToString()
{
string value = "The boolean value stored is : " + _value;
return value;
}
}
}

Set up constructor in C# abstraction

Consider the following very basic C# code.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
Random random = new Random();
for (int i = 1; i <= 100; i++)
{
int num = random.Next(1000);
string it_type;
if (num == 666)
{
System.Console.Write("Antichrist/satanistic trips get. Enjoy! ");
JonSkeet technician = new JonSkeet(); // Needs more Super::$tatic
technician.setup();
it_type = technician.getITType();
}
else
{
Whisperity technician = new Whisperity();
technician.setup();
it_type = technician.getITType();
}
System.Console.WriteLine(it_type + "... Prepare for next iteration.");
}
System.Console.ReadLine();
}
}
abstract public class ITTechnician
{
protected string itt_type = "Noname person.";
protected bool isJonSkeet = false;
public string getITType()
{
return this.itt_type;
}
abstract public void setup();
}
public class JonSkeet : ITTechnician
{
public override void setup()
{
this.itt_type = "Jon Skeet";
this.isJonSkeet = true;
}
}
public class Whisperity : ITTechnician
{
public override void setup()
{
this.itt_type = "Whisperity";
this.isJonSkeet = false;
}
}
}
How would I be able to set up a constructor in a way that the abstract class (abstract public void?) would require it and that I don't have to call technician.setup(); because the constructor takes care of setting the two internal variables. If I call the class functions the same name as the class itself, I get the following error:
Error 1 'Whisperity': member names cannot be the same as their enclosing
Also, my other question would be about optimization. Is there a way to define technician outside the if construct so something like the following could be executed: (This would omit having the classType technician = new classType(); lines twice, or is it unbypassable in C#?)
string it_type;
// Register 'technician' as a variable here.
if (num = 666)
{
technician = new JonSkeet();
}
else
{
technician = new Whisperity();
}
it_type = technician.getITType();
System.Console.WriteLine(it_type + "...");

Answer to your Question
You can provide a constructor with parameters in the abstract class.
abstract public class ITTechnician
{
public ITTechnician(string itt_type, bool isJonSkeet)
{
this.itt_type = itt_type;
this.isJonSkeet = isJonSkeet;
}
}
To construct a JonSkeet (if only it were so easy!)
JonSkeet jon = new JonSkeet("Jon Skeet", true);
Advice on Class Design
On a side note, I know this is a sample question, but you are not using object orientation well if a base class holds information that would differentiate classes that inherit from it.
Specifically this design would lead you to do things like
ITTechnician itt = GetSomeInstance();
if (itt.IsJonSkeet)
{
BehaviorA();
else
{
BehaviorB();
}
It is far cleaner to do something like
abstract public class ITTechnician
{
public abstract void Behavior();
// ...
}
public class JonSkeet
{
public override Behavior()
{
// Do awesome things
}
}
which allows the above code to be written as
ITTechnician itt = GetSomeInstance();
itt.Behavior();

How would I be able to set up a constructor in a way that the abstract
class would require it and that I don't have to call
technician.setup()
You don't need construct your logic to force the behavior of abstract class, but vice versa. Abstract class defines a stuf that has to be followed by the child.
If you create a simple parametless ctor in abstract class, which initializes the variables you need, whenever the child object will be constructed, the default ctor of abstract will be called before, so intialization will be executed.
To be more clear:
public class Child : Base
{
public Child(int x){
"Child".Dump();
}
}
public abstract class Base
{
public Base() {
//INIT VARIABLES HERE
"Base".Dump();
}
}
using these constructs like
vaar ch = new Child(); produces the result
"Base"
"Child"
If this is not what you're asking for, please clarify.

To discover a type at runtime, use GetType(). There's no need to create your own type string field.
The only thing that varies other than the intrinsic type in your class structure is IsJonSkeet. We can use a .NET property to implement this, which is a more modern and expressive way when compared to traditional private/protected fields with a Getter and maybe a Setter.
abstract public class ITTechnician
{
public bool IsJonSkeet { get; protected set; }
protected ITTechnician()
{
this.IsJonSkeet = false;
}
}
public class JonSkeet : ITTechnician
{
public JonSkeet()
{
this.IsJonSkeet = true;
}
}
public class Whisperity : ITTechnician
{
}
Now that your itt_type string field has been removed, Whisperity is the same as the base class, so there's no need for a constructor to do any initialisation - it will pick up the IsJonSkeet value of its parent automatically.
+1 for Eric J's class design tips, too. You should use the design of your hierarchy to encapsulate what varies and this makes your calling code much more transparent and the codebase easier to expand on in the future.

How to get value of abstract "const" property using reflection?

I've got a class defined like this:
public abstract class Uniform<T>
{
public abstract string GlslType { get; }
...
}
And then a subclass defined like this:
public class UniformInt : Uniform<int>
{
public override string GlslType
{
get { return "int"; }
}
}
And then a method somewhere else that looks like this:
public static string GetCode<T>()
{
var sb = new StringBuilder();
var type = typeof(T);
sb.AppendFormat("struct {0} {{\n", type.Name);
var fields = type.GetFields(BindingFlags.Public | BindingFlags.Instance);
foreach(var f in fields)
{
sb.AppendFormat(" {0} {1};\n", f.FieldType.GetProperty("GlslType").GetValue(???), f.Name);
}
...
}
I'm having trouble filling in the ???s. I believe GetValue expects an instance of the object, but I don't really care what instance it is because they all return the same value. And AFAIK there's no such thing as a public abstract static readonly value, so I have to use properties.
So what can I put in place of those ???s to get back "int" (assuming one the fields was a UniformInt).
As a side: How can I limit fields to only field types that inherit Uniform<>?

You need an instance of UniformInt in order to get the value of a non-static property:
UniformInt someUniformInt = ...
f.FieldType.GetProperty("GlslType").GetValue(someUniformInt, null)
As a side: How can I limit fields to only field types that inherit Uniform?
bool isDerivesFromUniformOfInt = typeof(Uniform<int>)
.IsAssignableFrom(f.FieldType);
or if you don't know the type of T in advance:
bool isDerivesFromUniformOfT = typeof(Uniform<>)
.MakeGenericType(typeof(T))
.IsAssignableFrom(f.FieldType);

The problem is that since your property is not static the compiler doesn't know that they all return the same value. Since your UniformInt is not sealed, another user could inherit from it and override GlslType to return something else. Then UniformInt and all derived classes could be used for your GetCode<T>() method.
A static method would really be the best option. To make sure that you implement them on all classes (something you can't force because static methods can't be abstract) I would write a simple unit test that uses reflection to load all classes that inherit from Uniform<T> and check if they have the static property defined.
UPDATE
When thinking about how Attributes could help and after some experimenting I came up with the following. It definitely won't win a beauty contest but as a learning exercise it was helpful ;)
using System;
using System.Linq;
namespace StackOverflow
{
internal class StackOverflowTest
{
private static void Main()
{
string sInt = UniformInt.GlslType;
string sDouble = UniformDouble.GlslType;
}
}
public abstract class Uniform<B, T> // Curiously recurring template pattern
where B : Uniform<B, T>
{
public static string GlslType
{
get
{
var attribute = typeof(B).GetCustomAttributes(typeof(GlslTypeAttribute), true);
if (!attribute.Any())
{
throw new InvalidOperationException(
"The GslType cannot be determined. Make sure the GslTypeAttribute is added to all derived classes.");
}
return ((GlslTypeAttribute)attribute[0]).GlslType;
}
}
}
[AttributeUsage(AttributeTargets.Class, Inherited = true, AllowMultiple = false)]
internal sealed class GlslTypeAttribute : Attribute
{
public string GlslType { get; private set; }
public GlslTypeAttribute(string glslType)
{
GlslType = glslType;
}
}
[GlslType("int")]
public class UniformInt : Uniform<UniformInt, int> // Curiously recurring template pattern
{
}
[GlslType("double")]
public class UniformDouble : Uniform<UniformDouble, double> // Curiously recurring template pattern
{
}
}

The GlslType is not static, so you need an object reference before you can access it's value. The subject of static properties in abstract classes has been covered extensively already, ie:
C#, implement 'static abstract' like methods
Can't define static abstract string property

Solution 1
Add static methods to all derived classes that return the GlslType. Nothing needs to be added to the base class. Can use unit testing + reflection to check for missing implementation. Suggested by Wouter de Kort.
Solution 2
Change Uniform<T> to make GlslType static:
public abstract class Uniform<T>
{
public static string GlslType { get { throw new NotImplementedException("Please override with \"new\" in derived class."); } }
...
}
Change UniformInt to "override" GlslType, keeping the static modifier:
public class UniformInt : Uniform<int>
{
public new static string GlslType
{
get { return "int"; }
}
}
Fill ??? with null, null:
sb.AppendFormat(" {0} {1};\n", f.FieldType.GetProperty("GlslType").GetValue(null,null), f.Name);
Solution 3
Use attributes instead. Something like:
[GlslType("int")]
public class UniformInt : Uniform<int>
{
}
Conclusion
All 3 of these solutions are pretty similar and seem to have the same drawbacks (can't enforce derived class to implement it). Throwing an exception via method 1 or 2 will help find errors quickly, or with 3 I can just skip over classes that don't have the attribute by modifying my fields condition.

Assigning a value to an inherited readonly field?

So I have a base class that has many children. This base class defines some readonly properties and variables that have default values. These can be different, depending on the child.
Readonly properties/fields allow you to change the value of the variable inside the constructor and also the definition, but nowhere else. I get a 'readonly variable can only be assigned to in a constructor' error if I try to change the value of an inherited readonly variable in the child class' constructor. Why is this and how can I work around this, without Reflection?
My intention: To allow user extensibility through scripts where they can only change certain fields once.

The reason is that you can only assign to readonly fields in the constructor of that class.
According to the definition of readonly in the C# Reference (emphasis mine):
When a field declaration includes a readonly modifier, assignments to the fields introduced by the declaration can only occur as part of the declaration or in a constructor in the same class.
To work around this, you could make a protected constructor in the base that takes a parameter for the readonly property.
An example:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
Base b = new Child();
Console.WriteLine(b.i);
Console.Read();
}
}
class Base
{
public readonly int i;
public Base()
{
i = 42;
}
protected Base(int newI)
{
i = newI;
}
}
class Child : Base
{
public Child()
: base(43)
{}
}
}

Adam has the right answer. If you're worried about the space it will take up (number of parameters in the constructor?) then you should address that as a different problem with a different solution: create a BaseConfig class, that contains all those properties and that is all that needs to be passed in. Base can then either assign all it's readonly fields from BaseConfig's properties, or you can instead have Base hold just one readonly field of type BaseConfig and refer to that for the values.
As to why this is, see C# constructor execution order regarding when each class's readonly fields would be initialized/initializable.

You could get the exact behavior you are looking for by using virtual get only properties.
public class BSE
{
virtual public int Prop
{
get
{
return 6;
}
}
}
public class Derived : BSE
{
public override int Prop
{
get
{
return 10;
}
}
}
Fields are out side the inheritance and overloading model and should not be used to provide polymorphic features.

You can use property with public get accessor and protected set accessor. Derived classes can set value of this property.
An example:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
Base b = new Child();
Console.WriteLine(b.I);
Console.Read();
}
}
class Base
{
public int I { get; protected set; }
public Base()
{
I = 42;
}
}
class Child : Base
{
public Child()
{
I = 43;
}
}
}

this is impossible by design. try passing the values to a protected base class constructor