Target-typed array creation

[rampaa]

Today, we need to create arrays like this:
private KeyValuePair<string, string>[] array = new KeyValuePair<string, string>[1024];
It would be great if we could instead write it in a simpler form, like this:
private KeyValuePair<string, string>[] array = new[1024];

I don't think this would introduce any ambiguity, though I could be wrong. If that's the case, feel free to correct me. As a user, I’d definitely expect the more concise version to just work™, so it's disappointing that it doesn't.

Semi-related discussions and issues: #8992, #100 (comment)

[alrz]

Would like to know if collection expression args could possibly support this.

List<int> list = [with(1024)]; // list with capacity?

Not quite sure about syntax here but perhaps this could be specialized for arrays?

[jnm2]

@CyrusNajmabadi int[] array = [with(1024)];, or int[] array = [args(1024)];, etc?

[lcsondes]

This is already valid, and it means something else:

using System.Collections.Generic;

class ExistingCode
{
    int with(int x) => x;
    int args(int y) => y;
	
    void foo()
    {
        List<int> x = [with(1024)];
        List<int> y = [args(1024)];
    }
}

[Trarizon]

@lcsondes Collection expressions args #8886 is another proposal that allows you to pass arguments to collection expression, the specific syntax isn't important here

[jnm2]

@lcsondes That might change.

[TizzyT566]

What's wrong with just

int[] arr = new[128];

This would be a nice addition imo.

If new syntax is required, maybe allow:

int[] arr = [..128];

We can extend this with indexing with ranges too:

int[] arr = [ ..128, 0..64:420, 64:19, 65..:666 ];

The implementation would just go through and see what is the highest index or lower/upper bound is to derive the size of the array.

If no value is specified default is implied.