Static rustc_lint::builtin::PATTERNS_IN_FNS_WITHOUT_BODY
source · pub static PATTERNS_IN_FNS_WITHOUT_BODY: &'static Lint
Expand description
The patterns_in_fns_without_body
lint detects mut
identifier
patterns as a parameter in functions without a body.
Example
trait Trait {
fn foo(mut arg: u8);
}
{{produces}}
Explanation
To fix this, remove mut
from the parameter in the trait definition;
it can be used in the implementation. That is, the following is OK:
trait Trait {
fn foo(arg: u8); // Removed `mut` here
}
impl Trait for i32 {
fn foo(mut arg: u8) { // `mut` here is OK
}
}
Trait definitions can define functions without a body to specify a
function that implementors must define. The parameter names in the
body-less functions are only allowed to be _
or an identifier for
documentation purposes (only the type is relevant). Previous versions
of the compiler erroneously allowed identifier patterns with the
mut
keyword, but this was not intended to be allowed. This is a
future-incompatible lint to transition this to a hard error in the
future. See issue #35203 for more details.