Fixed length arrays - Why (Question about syntax)

[worik]

If I have the code:

const fixed_thing[usize;3] = [1,2,3,4];

I get error:

29 |     const fixed_thing:[usize;3] = [1,2,3,4];
   |                                   ^^^^^^^^^ expected an array with a fixed size of 3 elements, found one with 4 elements
   |
   = note: expected type `[usize; 3]`
              found type `[usize; 4]`

Fair enough. Except why can I not write:

    const fixed_thing:[usize;] = [1,2,3,4];

The compiler has all the information that it needs to determine the size of the object. What am I missing?

[RustyYato]

This has been asked before

[Solved] Why can't the number of elements of const array be inferred?

Been running into the issue listed at https://stackoverflow.com/questions/23810032/how-to-specify-const-array-in-global-scope-in-rust. Specifically: const NUMBERS: [i32] = [1, 2, 3, 4, 5]; error[E0308]: mismatched types --> src/main.rs:2:28 | 2 | const NUMBERS: [i32] = [1, 2, 3, 4, 5]; | ^^^^^^^^^^^^^^^ expected slice, found array of 5 elements | = note: expected type `[i32]` = note: found type `[i32; 5]` error[E0277]: the trait bound `[i32]: std:…

https://github.com/rust-lang/rust/issues/40269

and const generics may help with it

Tracking issue for const generics (RFC 2000)