Creates a new deferred from a function.

template<
    typename Function>
constraint< !is_deferred< typename decay< Function >::type >::value, deferred_function< typename decay< Function >::type > >::type operator()(
    Function && function) const;
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Passes through anything that is already deferred.

template<
    typename T>
constraint< is_deferred< typename decay< T >::type >::value, typename decay< T >::type >::type operator()(
    T && t) const;
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