Proposal: argument name in Func and Action

[hez2010]

Proposal: argument name in Func and Action

Currently when we write Func<T1, T2, ...> func = (p1, p2, ...) => ..., we get a delegate without parameter names.
Therefore, when we want to invoke the delegate, IDE cannot prompt us the parameter name.

Func<int, int, int> myFunc = (x, y) => x + y; 

When we invoke it:

myFunc(  // IDE will prompt us 'arg1'
myFunc(1,  // IDE will prompt us 'arg2'

Solution

Allow argument name in Func and Action, just like what ValueTuple<T> did.

Func<int num1, int num2, int> myFunc = (x, y) => x + y; 

Then when we invoke it:

myFunc(  // IDE will prompt us 'num1'
myFunc(1,  // IDE will prompt us 'num2'

The same for Action<T, ...>.

[YairHalberstadt]

I have often wanted to name the types in Dictionaries. For example: Dictionary<int id, string name>

I think it wouldn't necessarily be a bad idea to be able to name type arguments in order to provide features for use of the IDE only.

[svick]

Related (and more ambitious) proposals: #470, #269.

[TonyValenti]

This reminds me of named members on tuples. Seems like a good idea.

[HaloFour]

I'd made the comment on other proposals but this only works in the narrow case where the named generic type argument is only used once for any given member or any given method signature. Delegates like Action<...> and Func<...> fit these constraints but only by convention. Same with tuples. But what happens when a type doesn't follow that convention?

public class Foo<T> {
    public void M(T x, T y) { }
}


var f = new Foo<int bar>();
f.M(...) // ?

[YairHalberstadt]

@HaloFour

If this was a purely IDE thing, I don't think it matters to much. The IDE could choose to display bar for both, bar for neither. Whatever.

The language just changes to allow you to put the name there. The meaning is left to the IDE to decide.

[HaloFour]

@YairHalberstadt

That feels a little weird if the language itself doesn't offer any support beyond just naming the generic type arguments. It makes the following feel really confusing:

Func<int x, int y, int y> f = (x, y) => x + y;
int result = f(arg1: 2, arg2: 3);

[YairHalberstadt]

@HaloFour
Do you mean the fact that the IDE shows them as named arguments, but you can't actually use named arguments?

[HaloFour]

@YairHalberstadt Exactly.

[magol]

Related to #894

[ufcpp]

Also related to #883

[ahdung]

On the contrary, I even want to remove the parameter name of delegate:
public delegate void Foo(string, int)

And the damned default value, it cause reflection doesn't respect method's default value.