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strongdef: disable mismatched T/Tag assignment

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Danny Robson 2015-11-25 13:32:29 +11:00
parent 93c08b048c
commit a3bdf1b7a1
1 changed files with 23 additions and 3 deletions
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26
strongdef.hpp
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@ -27,13 +27,33 @@ namespace util {
struct strongdef {
public:
using value_type = T;
using tag_type = Tag;
constexpr strongdef () = default;
constexpr explicit strongdef (const T &_data): data (_data) { ; }
constexpr strongdef (const strongdef &rhs): data (rhs.data) { ; }
strongdef& operator= (const strongdef &rhs) { data = rhs.data; return *this; }
strongdef& operator= (const T &rhs) { data = rhs; return *this; }
// explicitly disable assignment with unequal types or tags. this
// prevents the converion operator getting invoked and falsely
// allowing assignment with differing types or tags.
template <typename U, typename TagU>
std::enable_if_t<
!std::is_same<T,U>::value || !std::is_same<Tag,TagU>::value,
strongdef<T,Tag>&
>
operator= (const strongdef<U,TagU> &rhs) = delete;
template <typename U, typename TagU>
std::enable_if_t<
std::is_same<T,U>::value && std::is_same<Tag,TagU>::value,
strongdef<T,Tag>&
>
operator= (const strongdef<U,TagU> &rhs)
{ data = rhs.data; return *this; }
// simple value_type assignment.
strongdef& operator= (const T &rhs)
{ data = rhs; return *this; }
// conversion operators must not be explicit or it defeats the point
// of this class (ease of use, transparency).
@ -42,7 +62,7 @@ namespace util {
// explicitly disable equality with unequal types or tags. this
// prevents the conversion operator getting invoked and falsely
// allowing equality with different tags.
// allowing equality with different types or tags.
template <typename U, typename TagU>
std::enable_if_t<!std::is_same<T,U>::value || !std::is_same<Tag,TagU>::value,bool>
operator== (const strongdef<U,TagU> &rhs) = delete;