A binary assignment operator like += or ^= was applied to a type that
doesn’t support it.
Erroneous code example:
let mut x = 12f32; // error: binary operation `<<` cannot be applied to
// type `f32`
x <<= 2;To fix this error, please check that this type implements this binary operation. Example:
let mut x = 12u32; // the `u32` type does implement the `ShlAssign` trait
x <<= 2; // ok!It is also possible to overload most operators for your own type by
implementing the [OP]Assign traits from std::ops.
Another problem you might be facing is this: suppose you’ve overloaded the +
operator for some type Foo by implementing the std::ops::Add trait for
Foo, but you find that using += does not work, as in this example:
use std::ops::Add;
struct Foo(u32);
impl Add for Foo {
type Output = Foo;
fn add(self, rhs: Foo) -> Foo {
Foo(self.0 + rhs.0)
}
}
fn main() {
let mut x: Foo = Foo(5);
x += Foo(7); // error, `+= cannot be applied to the type `Foo`
}This is because AddAssign is not automatically implemented, so you need to
manually implement it for your type.