leo/docs/error-guides/parser/spread_in_array_init.md

Illegal spread expression in array initializer

Example

This error occurs when a spread expression, e.g., ...foo occurs in an array initializer.

Erroneous code example:

function main() {
    let foo = [0, 1];
    let array = [...foo; 3];
}

The compiler will reject this code with, for example...:

Error [EPAR0370010]: illegal spread in array initializer
    --> test.leo:3:17
     |
   3 |     let array = [...foo; 3];
     |                 ^^^^^^^

Solution

The Leo language does not allow ...foo as the element to repeat in an array repeat expression like the one above. This is because foo is not an element but rather a full array. One could imagine that the expression above means [...foo, ...foo, ...foo]. That is, ...foo repeated as many times as was specified in the array size. However, that is ambiguous with [element; 3] resulting in an array with size 3.

To solve the issue, disambiguate your intention. Most likely, you really wanted [...foo, ...foo, ...foo], so the solution is to write that out...:

function main() {
    let foo = [0, 1];
    let array = [...foo, ...foo, ...foo];
}