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# Error code E0435

A non-constant value was used in a constant expression.

Erroneous code example:

    #![allow(unused)]
    fn main() {
    let foo = 42;
    let a: [u8; foo]; // error: attempt to use a non-constant value in a constant
    }

‘constant’ means ‘a compile-time value’.

More details can be found in the Variables and Mutability section of the book.

To fix this error, please replace the value with a constant. Example:

    #![allow(unused)]
    fn main() {
    let a: [u8; 42]; // ok!
    }

Or:

    #![allow(unused)]
    fn main() {
    const FOO: usize = 42;
    let a: [u8; FOO]; // ok!
    }