I read the C++ version of this question but didn't really understand it.
Can someone please explain clearly if it can be done in C#, and how?
In C# 7 and above, see this answer.
In previous versions, you can use .NET 4.0+'s Tuple:
For Example:
public Tuple<int, int> GetMultipleValue()
{
return Tuple.Create(1,2);
}
Tuples with two values have Item1 and Item2 as properties.
Now that C# 7 has been released, you can use the new included Tuples syntax
(string, string, string) LookupName(long id) // tuple return type
{
... // retrieve first, middle and last from data storage
return (first, middle, last); // tuple literal
}
which could then be used like this:
var names = LookupName(id);
WriteLine($"found {names.Item1} {names.Item3}.");
You can also provide names to your elements (so they are not "Item1", "Item2" etc). You can do it by adding a name to the signature or the return methods:
(string first, string middle, string last) LookupName(long id) // tuple elements have names
or
return (first: first, middle: middle, last: last); // named tuple elements in a literal
They can also be deconstructed, which is a pretty nice new feature:
(string first, string middle, string last) = LookupName(id1); // deconstructing declaration
Check out this link to see more examples on what can be done :)
You can use three different ways
1. ref / out parameters
using ref:
static void Main(string[] args)
{
int a = 10;
int b = 20;
int add = 0;
int multiply = 0;
Add_Multiply(a, b, ref add, ref multiply);
Console.WriteLine(add);
Console.WriteLine(multiply);
}
private static void Add_Multiply(int a, int b, ref int add, ref int multiply)
{
add = a + b;
multiply = a * b;
}
using out:
static void Main(string[] args)
{
int a = 10;
int b = 20;
int add;
int multiply;
Add_Multiply(a, b, out add, out multiply);
Console.WriteLine(add);
Console.WriteLine(multiply);
}
private static void Add_Multiply(int a, int b, out int add, out int multiply)
{
add = a + b;
multiply = a * b;
}
2. struct / class
using struct:
struct Result
{
public int add;
public int multiply;
}
static void Main(string[] args)
{
int a = 10;
int b = 20;
var result = Add_Multiply(a, b);
Console.WriteLine(result.add);
Console.WriteLine(result.multiply);
}
private static Result Add_Multiply(int a, int b)
{
var result = new Result
{
add = a * b,
multiply = a + b
};
return result;
}
using class:
class Result
{
public int add;
public int multiply;
}
static void Main(string[] args)
{
int a = 10;
int b = 20;
var result = Add_Multiply(a, b);
Console.WriteLine(result.add);
Console.WriteLine(result.multiply);
}
private static Result Add_Multiply(int a, int b)
{
var result = new Result
{
add = a * b,
multiply = a + b
};
return result;
}
3. Tuple
Tuple class
static void Main(string[] args)
{
int a = 10;
int b = 20;
var result = Add_Multiply(a, b);
Console.WriteLine(result.Item1);
Console.WriteLine(result.Item2);
}
private static Tuple<int, int> Add_Multiply(int a, int b)
{
var tuple = new Tuple<int, int>(a + b, a * b);
return tuple;
}
C# 7 Tuples
static void Main(string[] args)
{
int a = 10;
int b = 20;
(int a_plus_b, int a_mult_b) = Add_Multiply(a, b);
Console.WriteLine(a_plus_b);
Console.WriteLine(a_mult_b);
}
private static (int a_plus_b, int a_mult_b) Add_Multiply(int a, int b)
{
return(a + b, a * b);
}
You cannot do this in C#. What you can do is have a out parameter or return your own class (or struct if you want it to be immutable).
Using out parameter
public int GetDay(DateTime date, out string name)
{
// ...
}
Using custom class (or struct)
public DayOfWeek GetDay(DateTime date)
{
// ...
}
public class DayOfWeek
{
public int Day { get; set; }
public string Name { get; set; }
}
In C#7 There is a new Tuple syntax:
static (string foo, int bar) GetTuple()
{
return ("hello", 5);
}
You can return this as a record:
var result = GetTuple();
var foo = result.foo
// foo == "hello"
You can also use the new deconstructor syntax:
(string foo) = GetTuple();
// foo == "hello"
Be careful with serialisation however, all this is syntactic sugar - in the actual compiled code this will be a Tuple<string, int> (as per the accepted answer) with Item1 and Item2 instead of foo and bar. That means that serialisation (or deserialisation) will use those property names instead.
So, for serialisation declare a record class and return that instead.
Also new in C#7 is an improved syntax for out parameters. You can now declare the out inline, which is better suited in some contexts:
if(int.TryParse("123", out int result)) {
// Do something with result
}
However, mostly you'll use this in .NET's own libraries, rather than in you own functions.
If you mean returning multiple values, you can either return a class/struct containing the values you want to return, or use the "out" keyword on your parameters, like so:
public void Foo(int input, out int output1, out string output2, out string errors) {
// set out parameters inside function
}
There is many way; but if you don't want to create a new Object or structure or something like this you can do like below after C# 7.0 :
(string firstName, string lastName) GetName(string myParameter)
{
var firstName = myParameter;
var lastName = myParameter + " something";
return (firstName, lastName);
}
void DoSomethingWithNames()
{
var (firstName, lastName) = GetName("myname");
}
Previous poster is right. You cannot return multiple values from a C# method. However, you do have a couple of options:
Return a structure that contains multiple members
Return an instance of a class
Use output parameters (using the out or ref keywords)
Use a dictionary or key-value pair as output
The pros and cons here are often hard to figure out. If you return a structure, make sure it's small because structs are value type and passed on the stack. If you return an instance of a class, there are some design patterns here that you might want to use to avoid causing problems - members of classes can be modified because C# passes objects by reference (you don't have ByVal like you did in VB).
Finally you can use output parameters but I would limit the use of this to scenarios when you only have a couple (like 3 or less) of parameters - otherwise things get ugly and hard to maintain. Also, the use of output parameters can be an inhibitor to agility because your method signature will have to change every time you need to add something to the return value whereas returning a struct or class instance you can add members without modifying the method signature.
From an architectural standpoint I would recommend against using key-value pairs or dictionaries. I find this style of coding requires "secret knowledge" in code that consumes the method. It must know ahead of time what the keys are going to be and what the values mean and if the developer working on the internal implementation changes the way the dictionary or KVP is created, it could easily create a failure cascade throughout the entire application.
You either return a class instance or use out parameters. Here's an example of out parameters:
void mymethod(out int param1, out int param2)
{
param1 = 10;
param2 = 20;
}
Call it like this:
int i, j;
mymethod(out i, out j);
// i will be 20 and j will be 10
Some answers suggest using out parameters but I recommend
not using this due to they don’t work with async methods. See
this for more information.
Other answers stated using Tuple, which I would recommend too but using the new feature introduced in C# 7.0.
(string, string, string) LookupName(long id) // tuple return type
{
... // retrieve first, middle and last from data storage
return (first, middle, last); // tuple literal
}
var names = LookupName(id);
WriteLine($"found {names.Item1} {names.Item3}.");
Further information can be found here.
<--Return more statements like this you can -->
public (int,string,etc) Sample( int a, int b)
{
//your code;
return (a,b);
}
You can receive code like
(c,d,etc) = Sample( 1,2);
I hope it works.
No, you can't return multiple values from a function in C# (for versions lower than C# 7), at least not in the way you can do it in Python.
However, there are a couple alternatives:
You can return an array of type object with the multiple values you want in it.
private object[] DoSomething()
{
return new [] { 'value1', 'value2', 3 };
}
You can use out parameters.
private string DoSomething(out string outparam1, out int outparam2)
{
outparam1 = 'value2';
outparam2 = 3;
return 'value1';
}
There are several ways to do this. You can use ref parameters:
int Foo(ref Bar bar) { }
This passes a reference to the function thereby allowing the function to modify the object in the calling code's stack. While this is not technically a "returned" value it is a way to have a function do something similar. In the code above the function would return an int and (potentially) modify bar.
Another similar approach is to use an out parameter. An out parameter is identical to a ref parameter with an additional, compiler enforced rule. This rule is that if you pass an out parameter into a function, that function is required to set its value prior to returning. Besides that rule, an out parameter works just like a ref parameter.
The final approach (and the best in most cases) is to create a type that encapsulates both values and allow the function to return that:
class FooBar
{
public int i { get; set; }
public Bar b { get; set; }
}
FooBar Foo(Bar bar) { }
This final approach is simpler and easier to read and understand.
In C# 4, you will be able to use built-in support for tuples to handle this easily.
In the meantime, there are two options.
First, you can use ref or out parameters to assign values to your parameters, which get passed back to the calling routine.
This looks like:
void myFunction(ref int setMe, out int youMustSetMe);
Second, you can wrap up your return values into a structure or class, and pass them back as members of that structure. KeyValuePair works well for 2 - for more than 2 you would need a custom class or struct.
you can try this "KeyValuePair"
private KeyValuePair<int, int> GetNumbers()
{
return new KeyValuePair<int, int>(1, 2);
}
var numbers = GetNumbers();
Console.WriteLine("Output : {0}, {1}",numbers.Key, numbers.Value);
Output :
Output : 1, 2
Classes, Structures, Collections and Arrays can contain multiple values. Output and reference parameters can also be set in a function. Return multiple values is possible in dynamic and functional languages by means of tuples, but not in C#.
When your method is async and you want to return multiple properties. You must do like this:
public async Task<(int, int)> GetMultipleValues(){
return (1,2);
}
Mainly two methods are there.
1. Use out/ref parameters
2. Return an Array of objects
Here are basic Two methods:
1) Use of 'out' as parameter
You can use 'out' for both 4.0 and minor versions too.
Example of 'out':
using System;
namespace out_parameter
{
class Program
{
//Accept two input parameter and returns two out value
public static void rect(int len, int width, out int area, out int perimeter)
{
area = len * width;
perimeter = 2 * (len + width);
}
static void Main(string[] args)
{
int area, perimeter;
// passing two parameter and getting two returning value
Program.rect(5, 4, out area, out perimeter);
Console.WriteLine("Area of Rectangle is {0}\t",area);
Console.WriteLine("Perimeter of Rectangle is {0}\t", perimeter);
Console.ReadLine();
}
}
}
Output:
Area of Rectangle is 20
Perimeter of Rectangle is 18
*Note:*The out-keyword describes parameters whose actual variable locations are copied onto the stack of the called method, where those same locations can be rewritten. This means that the calling method will access the changed parameter.
2) Tuple<T>
Example of Tuple:
Returning Multiple DataType values using Tuple<T>
using System;
class Program
{
static void Main()
{
// Create four-item tuple; use var implicit type.
var tuple = new Tuple<string, string[], int, int[]>("perl",
new string[] { "java", "c#" },
1,
new int[] { 2, 3 });
// Pass tuple as argument.
M(tuple);
}
static void M(Tuple<string, string[], int, int[]> tuple)
{
// Evaluate the tuple's items.
Console.WriteLine(tuple.Item1);
foreach (string value in tuple.Item2)
{
Console.WriteLine(value);
}
Console.WriteLine(tuple.Item3);
foreach (int value in tuple.Item4)
{
Console.WriteLine(value);
}
}
}
Output
perl
java
c#
1
2
3
NOTE: Use of Tuple is valid from Framework 4.0 and above.Tuple type is a class. It will be allocated in a separate location on the managed heap in memory. Once you create the Tuple, you cannot change the values of its fields. This makes the Tuple more like a struct.
A method taking a delegate can provide multiple values to the caller. This borrows from my answer here and uses a little bit from Hadas's accepted answer.
delegate void ValuesDelegate(int upVotes, int comments);
void GetMultipleValues(ValuesDelegate callback)
{
callback(1, 2);
}
Callers provide a lambda (or a named function) and intellisense helps by copying the variable names from the delegate.
GetMultipleValues((upVotes, comments) =>
{
Console.WriteLine($"This post has {upVotes} Up Votes and {comments} Comments.");
});
From this article, you can use three options as posts above said.
KeyValuePair is quickest way.
out is at the second.
Tuple is the slowest.
Anyway, this is depend on what is the best for your scenario.
Future version of C# is going to include named tuples.
Have a look at this channel9 session for the demo
https://channel9.msdn.com/Events/Build/2016/B889
Skip to 13:00 for the tuple stuff. This will allow stuff like:
(int sum, int count) Tally(IEnumerable<int> list)
{
// calculate stuff here
return (0,0)
}
int resultsum = Tally(numbers).sum
(incomplete example from video)
Just use in OOP manner a class like this:
class div
{
public int remainder;
public int quotient(int dividend, int divisor)
{
remainder = ...;
return ...;
}
}
The function member returns the quotient which most callers are primarily interested in. Additionally it stores the remainder as a data member, which is easily accessible by the caller afterwards.
This way you can have many additional "return values", very useful if you implement database or networking calls, where lots of error messages may be needed but only in case an error occurs.
I entered this solution also in the C++ question that OP is referring to.
You could use a dynamic object. I think it has better readability than Tuple.
static void Main(string[] args){
var obj = GetMultipleValues();
Console.WriteLine(obj.Id);
Console.WriteLine(obj.Name);
}
private static dynamic GetMultipleValues() {
dynamic temp = new System.Dynamic.ExpandoObject();
temp.Id = 123;
temp.Name = "Lorem Ipsum";
return temp;
}
Ways to do it:
1) KeyValuePair (Best Performance - 0.32 ns):
KeyValuePair<int, int> Location(int p_1, int p_2, int p_3, int p_4)
{
return new KeyValuePair<int,int>(p_2 - p_1, p_4-p_3);
}
2) Tuple - 5.40 ns:
Tuple<int, int> Location(int p_1, int p_2, int p_3, int p_4)
{
return new Tuple<int, int>(p_2 - p_1, p_4-p_3);
}
3) out (1.64 ns) or ref
4) Create your own custom class/struct
ns -> nanoseconds
Reference: multiple-return-values.
You can also use an OperationResult
public OperationResult DoesSomething(int number1, int number2)
{
// Your Code
var returnValue1 = "return Value 1";
var returnValue2 = "return Value 2";
var operationResult = new OperationResult(returnValue1, returnValue2);
return operationResult;
}
As an alternative you could set your method to void and not return anything. Instead create a public class with parameters and set them inside your method.
public class FooBar()
{
public string foo { get; set; }
public int bar { get; set; }
}
Then for your method try this
public void MyMethod(Foo foo, Bar bar)
{
FooBar fooBar = new FooBar();
fooBar.foo = "some string";
fooBar.bar = 1;
}
you can try this
public IEnumerable<string> Get()
{
return new string[] { "value1", "value2" };
}
Related
Is it possible to pass a function (like let's say sin() ) via string and then use it as int?
Like: (main idea only)
public int getfunc(String func)
{
return res_of(func)
}
I tried playing around with string of "Math.sin(0)"
but couldn't print the 0...
I could predefine the math functions since I only need 1 and then it becomes extremely simple as I only pass the int value for the function to work on, but I thought may-hap there is a way to keep it more generic.
I do not want to use mapping of the functions I want to keep it dynamic....
is ther a way of doing so?
I'd like to offer an alternative approach that you may not have considered.
You could use a delegate instead of passing a string; that way, you won't need any reflection.
There's a predefined delegate type in C# called Func<> which lets you easily define the return type and parameter types of a method that you want to pass as a delegate.
For example, the Func<> for Math.Sin(double) would be Func<double, double> because Math.Sin() returns a double and takes a double parameter.
An example will make this clearer:
using System;
namespace Demo
{
internal class Program
{
private void run()
{
Func<double, double> f1 = Math.Sin;
Func<double, double> f2 = Math.Cos;
double r1 = runFunc(f1, 1.0);
double r2 = runFunc(f2, 2.0);
Console.WriteLine(r1);
Console.WriteLine(r2);
}
private static double runFunc(Func<double, double> func, double parameter)
{
return func(parameter);
}
private static void Main()
{
new Program().run();
}
}
}
Try using http://www.csscript.net/
dynamic script = CSScript.Evaluator
.LoadCode(#"using System;
public class Script
{
public int Sum(int a, int b)
{
return a+b;
}
}");
int result = script.Sum(1, 2);
Declare the method like this:
public int DoCalculation(Func<double, double> func, double a)
{
return Convert.ToInt32(func(a));
}
Then use it like this:
int result = DoCalculation(Math.Sin, 3.3);
In our application we use the .NET integrated C# compiler.
This is some work to do but straight-forward to implement.
Here's an answer with a lot more details on that.
We use this in our companies production.
I'm making a library which will perform operations to read a processes memory, and get information from said process.
The problem I have is that to call the functions, I have to pass a lot of the variables every time, even if their values haven't changed.
For instance, ReadProcessMemory requires me to pass:
Process Handle
Memory Address
Main Module Base Address
Amount of bytes to read
The only thing that will be changing for each read is the Memory Address, so I don't really need to pass the rest of the variables every time I call the function (I actually have 3 functions which can be reduced in this way, and may have more shortly).
Could anyone give me a brief explanation as to how I should go about this? Will the variables exist at runtime so I can just call the function and use them directly from the DLL file?
You can use named parameters when calling methods with optional parameters.
public void MyMethod(string s = null, int i = 0, MyType t = null)
{
/* body */
}
Call it like so:
MyMethod(i: 10, t: new MyType());
MyMethod("abc");
MyMethod("abc", t: new MyType());
Alternatively you could use overloads:
public void MyMethod(string s)
{
MyMethod(s, 0, null);
}
public void MyMethod(int i)
{
MyMethod(null, i, null);
}
public void MyMethod(MyType t)
{
MyMethod(null, 0, t);
}
public void MyMethod(string s = null, int i = 0, MyType t = null)
{
/* body */
}
Yet another option is to use a parameters class like so:
public class MyParametersClass
{
public string s { get; set; }
public int i { get; set; }
public MyType t { get;set; }
public MyParametersClass()
{
// set defaults
s = null;
i = 0;
MyType = null;
}
}
public void MyMethod(MyParametersClass c)
{
/* body */
}
Calling like so:
MyMethod(new MyParametersClass
{
i = 25,
t = new MyType()
});
Using the parameters class is likely your preferred approach. The parameters class can be carried around as you process whatever you're processing. :) Any changes made to it will not be lost...
var parameters = new MyParametersClass();
MyMethod(parameters);
parameters.i = 26;
MyMethod(parameters);
One approach is to convert method call into object and have arguments cached in such object. Called refactoring to "method object".
Approximate sample (Tx - are some types):
int My.ReadProcessMemory(T1 a1, T2 a2, T3 variable)
{...}
class ReadProcessMemory
{
T1 a1;
T2 a2;
public ReadProcessMemory(T1 a1, T2 a2)
{
this.a1 = a1;
this.a2 = a2;
}
public int Run(T3 variable)
{
return My.ReadProcessMemory(a1, a2, variable);
}
}
Write a wrapper class for this ... set up the variable as properties or parms for the "new thing(...)" then subsequent calls are thing.Read(MemoryAddress)
In addition to using named parameters you will need to store the values that don't change in your library somehow.
If these are just runtime variables then you can just use class variables (if your library is a class) or static variables (if not). This does however, mean that your library is storing the state of the system and must verify that the state is still valid on every call.
Requiring the values to be passed in each call is actually a much cleaner interface and forces the users of your library to work in a consistent manner.
I'd like to pass a class property (or a getter/setter if need be) reference to a function.
For example I have an array of a class with lots of boolean flags.
class Flags
{
public bool a;
public bool b;
public bool c;
public string name;
public Flags(bool a, bool b, bool c, string name)
{
this.a = a;
this.b = b;
this.c = c;
this.name = name;
}
}
I can write a method that returns all instances of Flags for which a chosen flag is true
public Flags[] getAllWhereAisTrue(Flags[] array)
{
List<Flags> resultList = new List<Flags>();
for (int i = 0; i < array.Length; i++)
{
if (array[i].a == true) // for each Flags for which a is true
{ // add it to the results list
resultList.Add(array[i]);
}
}
return resultList.ToArray(); //return the results list as an array
}
What would I use to allow me to pass a class property as a parameter, so as to save me from having to write this method once for each boolean property of Flags (in this example that's three times, once for a, b and c)?
I'm trying to avoid giving Flags an array of Booleans in an attempt to keep the resulting code easy to read. I'm writing a library for use by relatively inexperienced coders.
Thank you
(With apologies if this is a dupe of Passing property as parameter in method, I can't quite tell if it's the same issue)
You could use a Func<Flags, bool> as parameter:
public Flags[] getAllWhereAisTrue(Flags[] array, Func<Flags, bool> propertySelector)
{
List<Flags> resultList = new List<Flags>();
for (int i = 0; i < array.Length; i++)
{
if (propertySelector(array[i])) // for each Flags for which a is true
{ // add it to the results list
resultList.Add(array[i]);
}
}
return resultList.ToArray(); //return the results list as an array
}
Then you could use it like this:
var allAFlagsSet = getAllWhereAisTrue(flagsArray, x=> x.a);
But really you should not reinvent this - Linq does this out of the box (notice the similarity):
var allAFlagsSet = flagsArray.Where(x=> x.a).ToArray();
Both solutions would require the a,b,c to be public (should really be a public property in this case)
according to the language spec it is not possible to pass properties as ref parameters. this stackoverflow post is on the same subject. moreover, I'll second the comment of SLaks: LINQ has a method that does just this.
I'm building a system a bit like LINQ, and in doing it, am trying to support polymorphic callback handler lists, and am running into several kinds of problems. The short way to ask my question is to just show you some code. My new system supports "Groups" and groups have a vector of entry points (below, UPDATE and CHECKPT) and each element on the vector is a polymorphic list of delegates, which I'll call back using reflection.
So, sample code:
namespace ConsoleApplication1
{
internal delegate void GroupISDHandler(int i, string s, double d);
class Group
{
public class myHandlers {
internal List<Delegate> hList = new List<Delegate>();
public static myHandlers operator +(myHandlers a, Delegate b) {
a.hList.Add(b);
return a;
}
}
public class mimicVector {
public List<myHandlers> ListofhLists = new List<myHandlers>();
public myHandlers this[int i] { get { return ListofhLists[i]; } set { ListofhLists[i] = value; } }
}
public mimicVector handlers = new mimicVector();
public Group(string name) { ... }
}
class Program
{
internal const int UPDATE = 0;
internal const int CHECKPT = 1;
public static void Main()
{
Group g = new Group("group name");
g.handlers[UPDATE] += (GroupISDHandler)delegate(int x, string s, double d) {
Console.WriteLine("my int,string,double handler was called, with x = {0}, s = {1}, d = {2}",
x,s,d);
};
}
}
}
My questions centers on the registration line. Why can't C# infer the types so that I could omit the cast and the new delegate type entirely? I would think that from
g.handlers[UPDATE] += delegate(int x, string s, double d) {
Console.WriteLine(....);
};
C# could infer the needed type signature. delegate() would be a kind of anonymous type and C# would just generate something like
private delegate void _atype1(int _a0, string _a1, double _a2)
and then insert (Delegate)(_atype1) before compiling the line. Thus my user won't need to declare a delegate type (which currently forces her to type the argument list twice, in effect).
I do have System.Linq since I'm on VS 2010. So if LINQ can somehow infer the needed casts...
you should be able to do it this way:
g.handlers[UPDATE] += (GroupISDHandler)((x, s, d) =>
Console.WriteLine(
"my int,string,double handler was called, with x = {0}, s = {1}, d = {2}",
x, s, d));
another option would be:
have a class named ´Parameters´ that is a container for whatever the user can send, might be defined types if they never change, or a list of objects if you pretend to send and receive different amount of parameters. Then instead of a Delegate, you would take Action that equals a delegate that takes one argument, and you could do your call without casting like this:
p => Console.WriteLine("x = {0}, s = {1}, d = {2}", p.x, p.s, p.d);
Turns out that the answer is basically this: while you can do the inference in the kinds of situations I had in mind, the C# owners want completely general solutions and polymorphism makes the type inference problem too hard to solve in a sufficiently general way, in their view. I myself disagree since I end up typing all my type signatures twice, but that's their reasoning.
Is it possible for a function to return two values?
Array is possible if the two values are both the same type, but how do you return two different type values?
Can a function return 2 separate values? No, a function in C# can only return a single value.
It is possible though to use other concepts to return 2 values. The first that comes to mind is using a wrapping type such as a Tuple<T1,T2>.
Tuple<int,string> GetValues() {
return Tuple.Create(42,"foo");
}
The Tuple<T1,T2> type is only available in 4.0 and higher. If you are using an earlier version of the framework you can either create your own type or use KeyValuePair<TKey,TValue>.
KeyValuePair<int,string> GetValues() {
return new KeyValuePair<int,sting>(42,"foo");
}
Another method is to use an out parameter (I would highly recomend the tuple approach though).
int GetValues(out string param1) {
param1 = "foo";
return 42;
}
In a word, no.
But you can define a struct (or class, for that matter) for this:
struct TwoParameters {
public double Parameter1 { get; private set; }
public double Parameter2 { get; private set; }
public TwoParameters(double param1, double param2) {
Parameter1 = param1;
Parameter2 = param2;
}
}
This of course is way too specific to a single problem. A more flexible approach would be to define a generic struct like Tuple<T1, T2> (as JaredPar suggested):
struct Tuple<T1, T2> {
public T1 Property1 { get; private set; }
public T2 Property2 { get; private set; }
public Tuple(T1 prop1, T2 prop2) {
Property1 = prop1;
Property2 = prop2;
}
}
(Note that something very much like the above is actually a part of .NET in 4.0 and higher, apparently.)
Then you might have some method that looks like this:
public Tuple<double, int> GetPriceAndVolume() {
double price;
int volume;
// calculate price and volume
return new Tuple<double, int>(price, volume);
}
And code like this:
var priceAndVolume = GetPriceAndVolume();
double price = priceAndVolume.Property1;
int volume = priceAndVolume.Property2;
It is not directly possible. You need to return a single parameter that wraps the two parameters, or use out parameters:
object Method(out object secondResult)
{
//...
Or:
KeyValuePair<object,object> Method()
{
// ..
All of the possible solutions miss one major point; why do you want to return two values from a method? The way I see it, there are two possible cases; a) you are returning two values that really should be encapsulated in one object (e.g. height and width of something, so you should return an object that represents that something) or b) this is a code smell and you really need to think about why the method is returning two values (e.g. the method is really doing two things).
with C# 7, you can now return a ValueTuple:
static (bool success, string value) GetValue(string key)
{
if (!_dic.TryGetValue(key, out string v)) return (false, null);
return (true, v); // this is a ValueType literal
}
static void Main(string[] args)
{
var (s, v) = GetValue("foo"); // (s, v) desconstructs the returned tuple
if (s) Console.WriteLine($"foo: {v}");
}
ValueTuple is a value-type, which makes it a great choice for a return value compared with a reference-type Tuple - no object needs to be garbage-collected.
Also, note that you can give a name to the values returned. It is really nice.
For that reason alone I wish it was possible to declare a ValueTuple with only one element. Alas, it is not allowed:
static (string error) Foo()
{
// ... does not work: ValueTuple must contain at least two elements
}
Not directly. Your options are either to return some kind of custom struct or class with multiple properties, use KeyValuePair if you simply want to return two values, or use out parameters.
You have basically (at least) two options, either you make an out parameter in addition to the return value of the function, something like T1 Function(out T2 second) or you make your own class putting these two types together, something like a Pair<T1,T2>. I personally prefer the second way but it's your choice.
In C# you can return more than one value using an out parameter. See example in the TryParse method of Int32 struct. It returns bool and an integer in an out parameter.
no but you can use an out parameter
int whatitis;
string stuff = DoStuff(5, out whatitis);
public string DoStuff(int inParam, out int outParam)
{
outParam = inParam + 10;
return "donestuff";
}
It is not possible to return more than one value from a function, unless you are returning a type that contains multiple values in it (Struct, Dictionary, etc). The only other way would be to use the "out" or "ref" keywords on the incoming parameters.
You could use the out parameter.
int maxAge;
int minAge;
public int GetMaxAgeAndMinAge(out int maxAge, out int minAge)
{
MaxAge = 60;
MinAge = 0;
return 1; //irrelevant for this example since we care about the values we pass in
}
I really tend to stay away from this, I think that it is a code-smell. It works for quick and dirty though. A more testable and better approach would be to pass an object that represents your domain (the need to see two these two values).
you can try this
public IEnumerable<string> Get()
{
return new string[] { "value1", "value2" };
}
To return 2 values I usually use Pair class from http://blog.o-x-t.com/2007/07/16/generic-pair-net-class/.
If you need to return from method 2 values that describe the range, e.g. From/To or Min/Max, you can use FromToRange class.
public class FromToRange<T>
{
public T From { get; set; }
public T To { get; set; }
public FromToRange()
{
}
public FromToRange(T from, T to)
{
this.From = from;
this.To = to;
}
public override string ToString()
{
string sRet = String.Format("From {0} to {1}", From, To);
return sRet;
}
public override bool Equals(object obj)
{
if (this == obj) return true;
FromToRange<T> pair = obj as FromToRange<T>;
if (pair == null) return false;
return Equals(From, pair.From) && Equals(To, pair.To);
}
public override int GetHashCode()
{
return (From != null ? From.GetHashCode() : 0) + 29 * (To != null ? To.GetHashCode() : 0);
}
}