An associated const has been referenced in a pattern.
Erroneous code example:
```compile_fail,E0158
enum EFoo { A, B, C, D }
trait Foo {
const X: EFoo;
}
fn test<A: Foo>(arg: EFoo) {
match arg {
A::X => { // error!
println!("A::X");
}
}
}
```
`const` and `static` mean different things. A `const` is a compile-time
constant, an alias for a literal value. This property means you can match it
directly within a pattern.
The `static` keyword, on the other hand, guarantees a fixed location in memory.
This does not always mean that the value is constant. For example, a global
mutex can be declared `static` as well.
If you want to match against a `static`, consider using a guard instead:
```
static FORTY_TWO: i32 = 42;
match Some(42) {
Some(x) if x == FORTY_TWO => {}
_ => {}
}
```