Static rustc_lint::traits::DROP_BOUNDS
source · pub static DROP_BOUNDS: &Lint
Expand description
The drop_bounds
lint checks for generics with std::ops::Drop
as
bounds.
Example
fn foo<T: Drop>() {}
{{produces}}
Explanation
A generic trait bound of the form T: Drop
is most likely misleading
and not what the programmer intended (they probably should have used
std::mem::needs_drop
instead).
Drop
bounds do not actually indicate whether a type can be trivially
dropped or not, because a composite type containing Drop
types does
not necessarily implement Drop
itself. Naïvely, one might be tempted
to write an implementation that assumes that a type can be trivially
dropped while also supplying a specialization for T: Drop
that
actually calls the destructor. However, this breaks down e.g. when T
is String
, which does not implement Drop
itself but contains a
Vec
, which does implement Drop
, so assuming T
can be trivially
dropped would lead to a memory leak here.
Furthermore, the Drop
trait only contains one method, Drop::drop
,
which may not be called explicitly in user code (E0040
), so there is
really no use case for using Drop
in trait bounds, save perhaps for
some obscure corner cases, which can use #[allow(drop_bounds)]
.