Construct an any_completion_handler in an empty state, without a target object.

constexpr any_completion_handler();
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constexpr any_completion_handler(
    nullptr_t );
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Construct an any_completion_handler to contain the specified target.

template<
    typename H,
    typename Handler = decay_t<H>>
any_completion_handler(
    H && h,
    constraint_t< !is_same< decay_t< H >, any_completion_handler >::value >  = 0);
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Move-construct an any_completion_handler from another.

any_completion_handler(
    any_completion_handler && other);
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