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230 lines
6.8 KiB
C++
230 lines
6.8 KiB
C++
/*=============================================================================
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Copyright (c) 2014 Paul Fultz II
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returns.h
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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==============================================================================*/
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#ifndef FIT_GUARD_RETURNS_H
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#define FIT_GUARD_RETURNS_H
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/// returns
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/// =======
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///
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/// Description
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/// -----------
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///
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/// The `FIT_RETURNS` macro helps deduce the return type of an expression
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/// using the trailing return type. Instead of repeating the expression for
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/// the return type and using the expression in the function body, this macro
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/// helps reduce the code duplication from that.
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///
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/// Note: The expression used to deduce the return the type will also
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/// constrain the template function as well, which is different behaviour than
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/// using C++14's return type deduction.
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///
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/// Synopsis
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/// --------
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///
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/// #define FIT_RETURNS(...)
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///
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///
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/// Example
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/// -------
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///
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/// template<class T, class U>
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/// auto sum(T x, U y) FIT_RETURNS(x+y);
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///
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/// assert(3 == sum(1, 2));
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///
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///
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/// Incomplete this
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/// ===============
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///
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/// Description
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/// -----------
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///
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/// On older compilers the `this` variable cannot be used inside the
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/// `FIT_RETURNS` macro because it is considered an incomplete type. So the
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/// following macros are provided to help workaround the issue.
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///
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///
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/// Synopsis
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/// --------
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///
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/// // Declares the type of the `this` variable
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/// #define FIT_RETURNS_CLASS(...)
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/// // Used to refer to the `this` variable in the FIT_RETURNS macro
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/// #define FIT_THIS
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/// // Used to refer to the const `this` variable in the FIT_RETURNS macro
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/// #define FIT_CONST_THIS
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///
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///
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/// Example
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/// -------
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///
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/// struct add_1
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/// {
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/// int a;
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/// add_1() : a(1) {}
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///
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/// FIT_RETURNS_CLASS(add_1)
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///
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/// template<class T>
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/// auto operator()(T x) const
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/// FIT_RETURNS(x+FIT_CONST_THIS->a);
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/// };
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///
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/// assert(3 == add_1()(2));
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///
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///
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/// Mangling overloads
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/// ==================
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///
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/// Description
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/// -----------
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///
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/// On older compilers some operations done in the expressions cannot be
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/// properly mangled. These macros help provide workarounds for these
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/// operations on older compilers.
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///
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///
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/// Synopsis
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/// --------
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///
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/// // Explicitly defines the type for name mangling
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/// #define FIT_MANGLE_CAST(...)
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/// // C cast for name mangling
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/// #define FIT_RETURNS_C_CAST(...)
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/// // Reinterpret cast for name mangling
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/// #define FIT_RETURNS_REINTERPRET_CAST(...)
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/// // Static cast for name mangling
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/// #define FIT_RETURNS_STATIC_CAST(...)
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/// // Construction for name mangling
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/// #define FIT_RETURNS_CONSTRUCT(...)
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///
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#ifndef FIT_HAS_MANGLE_OVERLOAD
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#if defined(__GNUC__) && !defined (__clang__) && __GNUC__ == 4 && __GNUC_MINOR__ < 7
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#define FIT_HAS_MANGLE_OVERLOAD 0
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#else
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#define FIT_HAS_MANGLE_OVERLOAD 1
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#endif
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#endif
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#ifndef FIT_HAS_COMPLETE_DECLTYPE
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#if !FIT_HAS_MANGLE_OVERLOAD || (defined(__GNUC__) && !defined (__clang__) && __GNUC__ == 4 && __GNUC_MINOR__ < 8)
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#define FIT_HAS_COMPLETE_DECLTYPE 0
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#else
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#define FIT_HAS_COMPLETE_DECLTYPE 1
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#endif
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#endif
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#include <utility>
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#include <fit/detail/forward.h>
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#define FIT_EAT(...)
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#define FIT_REM(...) __VA_ARGS__
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#if FIT_HAS_COMPLETE_DECLTYPE && FIT_HAS_MANGLE_OVERLOAD
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#define FIT_RETURNS(...) -> decltype(__VA_ARGS__) { return __VA_ARGS__; }
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#define FIT_THIS this
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#define FIT_CONST_THIS this
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#define FIT_RETURNS_CLASS(...) \
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void fit_returns_class_check() \
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{ \
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static_assert(std::is_same<__VA_ARGS__*, decltype(this)>::value, \
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"Returns class " #__VA_ARGS__ " type doesn't match"); \
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}
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#define FIT_MANGLE_CAST(...) FIT_REM
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#define FIT_RETURNS_C_CAST(...) (__VA_ARGS__) FIT_REM
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#define FIT_RETURNS_REINTERPRET_CAST(...) reinterpret_cast<__VA_ARGS__>
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#define FIT_RETURNS_STATIC_CAST(...) static_cast<__VA_ARGS__>
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#define FIT_RETURNS_CONSTRUCT(...) __VA_ARGS__
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#else
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#include <fit/detail/pp.h>
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#define FIT_RETURNS_RETURN(...) return FIT_RETURNS_RETURN_X(FIT_PP_WALL(__VA_ARGS__))
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#define FIT_RETURNS_RETURN_X(...) __VA_ARGS__
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#define FIT_RETURNS_DECLTYPE(...) decltype(FIT_RETURNS_DECLTYPE_CONTEXT(__VA_ARGS__))
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#define FIT_RETURNS_DECLTYPE_CONTEXT(...) FIT_RETURNS_DECLTYPE_CONTEXT_X(FIT_PP_WALL(__VA_ARGS__))
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#define FIT_RETURNS_DECLTYPE_CONTEXT_X(...) __VA_ARGS__
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#define FIT_RETURNS_THAT(...) FIT_PP_IIF(FIT_PP_IS_PAREN(FIT_RETURNS_DECLTYPE_CONTEXT(())))(\
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(fit::detail::check_this<__VA_ARGS__, decltype(this)>(), this), \
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std::declval<__VA_ARGS__>() \
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)
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#define FIT_THIS FIT_PP_RAIL(FIT_RETURNS_THAT)(fit_this_type)
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#define FIT_CONST_THIS FIT_PP_RAIL(FIT_RETURNS_THAT)(fit_const_this_type)
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#define FIT_RETURNS_CLASS(...) typedef __VA_ARGS__* fit_this_type; typedef const __VA_ARGS__* fit_const_this_type
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#define FIT_RETURNS(...) -> FIT_RETURNS_DECLTYPE(__VA_ARGS__) { FIT_RETURNS_RETURN(__VA_ARGS__); }
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namespace fit { namespace detail {
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template<class Assumed, class T>
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struct check_this
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{
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static_assert(std::is_same<T, Assumed>::value, "Incorret FIT_THIS or FIT_CONST_THIS used.");
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};
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}}
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#endif
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#if FIT_HAS_MANGLE_OVERLOAD
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#define FIT_MANGLE_CAST(...) FIT_REM
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#define FIT_RETURNS_C_CAST(...) (__VA_ARGS__) FIT_REM
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#define FIT_RETURNS_REINTERPRET_CAST(...) reinterpret_cast<__VA_ARGS__>
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#define FIT_RETURNS_STATIC_CAST(...) static_cast<__VA_ARGS__>
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#define FIT_RETURNS_CONSTRUCT(...) __VA_ARGS__
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#else
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#define FIT_RETURNS_DERAIL_MANGLE_CAST(...) FIT_PP_IIF(FIT_PP_IS_PAREN(FIT_RETURNS_DECLTYPE_CONTEXT(())))(\
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FIT_REM, \
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std::declval<__VA_ARGS__>() FIT_EAT \
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)
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#define FIT_MANGLE_CAST FIT_PP_RAIL(FIT_RETURNS_DERAIL_MANGLE_CAST)
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#define FIT_RETURNS_DERAIL_C_CAST(...) FIT_PP_IIF(FIT_PP_IS_PAREN(FIT_RETURNS_DECLTYPE_CONTEXT(())))(\
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(__VA_ARGS__) FIT_REM, \
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std::declval<__VA_ARGS__>() FIT_EAT \
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)
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#define FIT_RETURNS_C_CAST FIT_PP_RAIL(FIT_RETURNS_DERAIL_C_CAST)
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#define FIT_RETURNS_DERAIL_REINTERPRET_CAST(...) FIT_PP_IIF(FIT_PP_IS_PAREN(FIT_RETURNS_DECLTYPE_CONTEXT(())))(\
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reinterpret_cast<__VA_ARGS__>, \
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std::declval<__VA_ARGS__>() FIT_EAT \
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)
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#define FIT_RETURNS_REINTERPRET_CAST FIT_PP_RAIL(FIT_RETURNS_DERAIL_REINTERPRET_CAST)
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#define FIT_RETURNS_DERAIL_STATIC_CAST(...) FIT_PP_IIF(FIT_PP_IS_PAREN(FIT_RETURNS_DECLTYPE_CONTEXT(())))(\
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static_cast<__VA_ARGS__>, \
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std::declval<__VA_ARGS__>() FIT_EAT \
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)
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#define FIT_RETURNS_STATIC_CAST FIT_PP_RAIL(FIT_RETURNS_DERAIL_STATIC_CAST)
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#define FIT_RETURNS_DERAIL_CONSTRUCT(...) FIT_PP_IIF(FIT_PP_IS_PAREN(FIT_RETURNS_DECLTYPE_CONTEXT(())))(\
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__VA_ARGS__, \
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std::declval<__VA_ARGS__>() FIT_EAT \
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)
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#define FIT_RETURNS_CONSTRUCT FIT_PP_RAIL(FIT_RETURNS_DERAIL_CONSTRUCT)
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#endif
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#define FIT_AUTO_FORWARD(x) fit::forward<decltype(x)>(x)
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#endif |