Error code E0493
A value with a custom Drop
implementation may be dropped during const-eval.
Erroneous code example:
#![allow(unused)] fn main() { enum DropType { A, } impl Drop for DropType { fn drop(&mut self) {} } struct Foo { field1: DropType, } static FOO: Foo = Foo { field1: (DropType::A, DropType::A).1 }; // error! }
The problem here is that if the given type or one of its fields implements the
Drop
trait, this Drop
implementation cannot be called within a const
context since it may run arbitrary, non-const-checked code. To prevent this
issue, ensure all values with a custom Drop
implementation escape the
initializer.
#![allow(unused)] fn main() { enum DropType { A, } impl Drop for DropType { fn drop(&mut self) {} } struct Foo { field1: DropType, } static FOO: Foo = Foo { field1: DropType::A }; // We initialize all fields // by hand. }