Header file compiles.hpp

#define SIPLASPLAS_UTILITY_COMPILES_HPP 

#include "meta.hpp"

#include "identity.hpp"

#define SIPLASPLAS_UTILITY_COMPILES(...) \
        ::cpp::compiles(                                  \
            [](auto identity) -> decltype(__VA_ARGS__) {} \
        )

namespace cpp
{
    namespace detail
    {
        template <typename Expr>
        class Compiles;
    }
    
    template <typename Expr>
    constexpr auto compiles(Expr&& expr);
}

Macro SIPLASPLAS_UTILITY_COMPILES

#define SIPLASPLAS_UTILITY_COMPILES(...) \
        ::cpp::compiles(                                  \
            [](auto identity) -> decltype(__VA_ARGS__) {} \
        )

This macro hides the syntax complexity of cpp::compiles() and checks directly whatever expression is passed as argument to the macro:

auto result = SIPLASPLAS_UTILITY_COMPILES(
    identity(std::declval<std::string>()).append("hello")
);

static_assert(!result, "std::string has no append() method");

Note there’s an implicit identity variable available to delay the evaluation of the expression.

Returns: An implementation defined type constexpr-convertible to bool. The returned value converts to true if the expression is well formed, converts to false otherwise.

Function template cpp::compiles<Expr>

template <typename Expr>
constexpr auto compiles(Expr&& expr);

This function takes an expression in the form of an SFINAE-friendly context and checks if the expression can be compiled. For example:

auto result = cpp::compiles([](auto identity) -> decltype(
    identity(std::declval<std::string>()).append("hello")
) {});

static_assert(!result, "std::string has no append() method");

The cpp::compiles(<test>) expression itself is not constexpr, so two steps are needed to perform the constexpr test. cpp::compiles() returns an implementation defined type that is constexpr-convertible to bool, giving the result of the test.

Returns: An implementation defined type constexpr-convertible to bool. The returned value converts to true if the expression is well formed, converts to false otherwise.

Parameter cpp::compiles::expr

Expr&& expr

A callable template of signature decltype(<expression to check>)(Identity). The identity parameter is given to delay the evaluation of the expression, making it dependent of a template of the test. If the expression is directly evaluable, an ill-formed expression would make the program compilation to fail.