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