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Diffstat (limited to 'libbutl/multi-index.hxx')
-rw-r--r-- | libbutl/multi-index.hxx | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/libbutl/multi-index.hxx b/libbutl/multi-index.hxx new file mode 100644 index 0000000..a6754cd --- /dev/null +++ b/libbutl/multi-index.hxx @@ -0,0 +1,57 @@ +// file : libbutl/multi-index.hxx -*- C++ -*- +// license : MIT; see accompanying LICENSE file + +#pragma once + +#include <utility> // declval() +#include <functional> // hash + +#include <libbutl/export.hxx> + +namespace butl +{ + // Google the "Emulating Boost.MultiIndex with Standard Containers" blog + // post for details. + // + + template <typename T> + struct map_key + { + mutable const T* p; + + map_key (const T* v = 0): p (v) {} + bool operator< (const map_key& x) const {return *p < *x.p;} + bool operator== (const map_key& x) const {return *p == *x.p;} + }; + + template <typename I> + struct map_iterator_adapter: I + { + typedef const typename I::value_type::second_type value_type; + typedef value_type* pointer; + typedef value_type& reference; + + map_iterator_adapter () {} + map_iterator_adapter (I i): I (i) {} + + map_iterator_adapter& + operator= (I i) {static_cast<I&> (*this) = i; return *this;} + + reference operator* () const {return I::operator* ().second;} + pointer operator-> () const {return &I::operator-> ()->second;} + }; +} + +namespace std +{ + template <typename T> + struct hash<butl::map_key<T>>: hash<T> + { + size_t + operator() (butl::map_key<T> x) const + noexcept (noexcept (declval<hash<T>> () (*x.p))) + { + return hash<T>::operator() (*x.p); + } + }; +} |