pub static CONST_PATTERNS_WITHOUT_PARTIAL_EQ: &'static Lint
Expand description
The const_patterns_without_partial_eq
lint detects constants that are used in patterns,
whose type does not implement PartialEq
.
Example
ⓘ
#![deny(const_patterns_without_partial_eq)]
trait EnumSetType {
type Repr;
}
enum Enum8 { }
impl EnumSetType for Enum8 {
type Repr = u8;
}
#[derive(PartialEq, Eq)]
struct EnumSet<T: EnumSetType> {
__enumset_underlying: T::Repr,
}
const CONST_SET: EnumSet<Enum8> = EnumSet { __enumset_underlying: 3 };
fn main() {
match CONST_SET {
CONST_SET => { /* ok */ }
_ => panic!("match fell through?"),
}
}
{{produces}}
Explanation
Previous versions of Rust accepted constants in patterns, even if those constants’ types
did not have PartialEq
implemented. The compiler falls back to comparing the value
field-by-field. In the future we’d like to ensure that pattern matching always
follows PartialEq
semantics, so that trait bound will become a requirement for
matching on constants.