Defined in header <experimental/type_traits>
struct nonesuch {

    ~nonesuch() = delete;
    nonesuch(nonesuch const&) = delete;
    void operator=(nonesuch const&) = delete;

(library fundamentals TS v2)

std::experimental::nonesuch is a class type used by std::experimental::detected_t to indicate detection failure.

nonesuch has no default constructor or initializer-list constructor, and is not an aggregate.


nonesuch cannot be constructed, destroyed, or copied.

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2960 LFTSv2 nonesuch may be an aggregate and has an implicit conversion sequence from {} made non-aggregate and removed ICS