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Array expression repeat operands can be const blocks. #1928

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Jul 8, 2025
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Array expression repeat operands can be const blocks. #1928

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9 changes: 5 additions & 4 deletions src/expressions/array-expr.md
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Expand Up @@ -53,16 +53,16 @@ An array expression of this form creates an array with the length of the value o
That is, `[a; b]` creates an array containing `b` copies of the value of `a`.

r[expr.array.repeat-copy]
If the length operand has a value greater than 1 then this requires that the type of the repeat operand is [`Copy`] or that it must be a [path] to a constant item.
If the length operand has a value greater than 1 then this requires the repeat operand to have a type that implements [`Copy`], to be a [const block expression], or to be a [path] to a constant item.

r[expr.array.repeat-const-item]
When the repeat operand is a constant item, it is evaluated the length operand's value times.
When the repeat operand is a const block or a path to a constant item, it is evaluated the number of times specified in the length operand.

r[expr.array.repeat-evaluation-zero]
If that value is `0`, then the constant item is not evaluated at all.
If that value is `0`, then the const block or constant item is not evaluated at all.

r[expr.array.repeat-non-const]
For expressions that are not a constant item, it is evaluated exactly once, and then the result is copied the length operand's value times.
For expressions that are neither a const block nor a path to a constant item, it is evaluated exactly once, and then the result is copied the length operand's value times.

```rust
[1, 2, 3, 4];
Expand Down Expand Up @@ -123,6 +123,7 @@ The array index expression can be implemented for types other than arrays and sl
[Index]: std::ops::Index
[array]: ../types/array.md
[const generic argument]: items.generics.const.argument
[const block expression]: expr.block.const
[constant expression]: ../const_eval.md#constant-expressions
[constant item]: ../items/constant-items.md
[inferred const]: items.generics.const.inferred
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