1+++
2title = "`const error_type &assume_error() const & noexcept`"
3description = "Narrow contract const lvalue reference observer of the stored error. Constexpr propagating, never throws."
4categories = ["observers"]
5weight = 710
6+++
7
8Narrow contract const lvalue reference observer of the stored error. `NoValuePolicy::narrow_error_check()` is first invoked, then the reference to the error is returned. As a valid default constructed error is always present, no undefined behaviour occurs unless `NoValuePolicy::narrow_error_check()` does that.
9
10Note that if `error_type` is `void`, only a `const` overload returning `void` is present.
11
12*Requires*: Always available.
13
14*Complexity*: Depends on `NoValuePolicy::narrow_error_check()`.
15
16*Guarantees*: An exception is never thrown.
17