Allow implicitly typed variable(var) in methods optional paramters

[imranbaloch]

Let's say we have this method,

public void SomeMethod(string str = "", int id = -1)
{
}

It will be great if we have something like,

public void SomeMethod(var str = "", var id = -1)
{
}

Due to optional parameter, compiler can easily determines the type. Just a suggestion.

[DavidArno]

Um, how do you propose that the compiler work out that var str = null is of type string, as opposed to any other reference type?

[dsaf]

It will be great if we have something like...

Why? It's not likely to be something like Dictionary<Dictionary<string, Tuple<string, decimal>>> due to type limitation. The type names are likely to be quite short. Even your example only saves 3 characters.

[alrz]

As @DavidArno said, for all default values (null, zero and other structs) you will require to specify the type anyways. I'd prefer #7737 as it helps with consistency, conciseness and DRY.

void SomeMethod(string str = default, int id = default, CancellationToken ct = default)

As for non-default values like -1 I don't think that it needs to be different as it doesn't even save a single keystroke. Moreover, inferring public contract from usage doesn't seem to be a good idea overall.

[imranbaloch]

@DavidArno oh sorry I mean,

string str = "".

What I mean is that when we can do

var s = "";

why not this,

someMethod(var s = "")

[DavidArno]

why not this,
someMethod(var s = "")

I'm no fan of default/optional parameters and would always go for the following instead:

someMethod() => ...
someMethodWithString(string s) => ...

[gafter]

Closing as this doesn't appear to have much support. Having said that, if you want to continue to pursue this discussion, please open a new thread in csharplang.