# Error code E0074

#### Note: this error code is no longer emitted by the compiler.

When using the `#[simd]` attribute on a tuple struct, the components of the tuple struct must all be of a concrete, nongeneric type so the compiler can reason about how to use SIMD with them. This error will occur if the types are generic.

This will cause an error:

    #![allow(unused)]
    #![feature(repr_simd)]

    fn main() {
    #[repr(simd)]
    struct Bad<T>(T, T, T, T);
    }

This will not:

    #![allow(unused)]
    #![feature(repr_simd)]

    fn main() {
    #[repr(simd)]
    struct Good(u32, u32, u32, u32);
    }