Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

Default constructor.

constexpr as_single_t(
    default_constructor_tag  = default_constructor_tag(),
    CompletionToken token = CompletionToken());
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Constructor.

template<
    typename T>
explicit constexpr as_single_t(
    T && completion_token);
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