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A binary assignment operator like `+=` or `^=` was applied to a type that
doesn't support it.
Erroneous code example:
```compile_fail,E0368
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:
```compile_fail,E0368
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.
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