Cannot return a local array

Meaning

Array literals are stack allocated. Returning a local array would expose storage after its function frame ends.

Although arrays use copy behavior in ordinary local assignment, the current source type/lowering does not provide a caller-owned return representation for a local stack array.

Why it happens

[T] resembles an ordinary value type, but its length is tied to initializer/compiler storage rather than a source-spelled fixed-size ABI. The escape check prevents a dangling frame reference.

Invalid code

fn make() -> [Int] {
    let values = [1, 2, 3]
    return values
}
fn main() -> Int { return 0 }

Correct code

fn first() -> Int {
    let values = [1, 2, 3]
    return values[0]
}
fn main() -> Int { return first() }

Common fixes

Consume the array inside the function, return a copyable element/result, or use an owned list when data must escape.

When the caller already owns a List<T>, a function may instead return a Slice<T> that views a bounded range of that list. A Slice cannot view a local stack array, and it is not an FFI output-buffer ABI. Do not use Ptr casts to bypass the lifetime check.