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Make iterator_result_converter satisfy std::ranges::range

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std::ranges::range requires the iterator to be default-constructible and
have postfix operator++.  Add those to satisfy the concept.
This commit is contained in:
Kp 2023-01-14 19:05:37 +00:00
parent 9fd0cc96a5
commit 932c8370d5
1 changed files with 29 additions and 0 deletions
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29
common/main/cast_range_result.h
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@ -11,9 +11,28 @@
#include "partial_range.h"
template <typename result_type, typename iterator_type>
/* Declare the requirements on the class itself, rather than the one method which needs them, because:
* - the class is useless if that one method fails its requirements
* - gcc produces better error messages if the class is rejected, than if the
* class is accepted and `operator*()` is rejected.
*/
requires(
requires(iterator_type i) {
/* If the base type's result cannot be converted to this type's result,
* then `operator*()` will raise an error when it attempts an implicit
* conversion.
*/
{*i} -> std::convertible_to<result_type>;
/* If `result_type` and the base type's `operator*` are the same, then
* this adapter has no effect.
*/
requires(!std::is_same<result_type, decltype(*i)>::value);
}
)
class iterator_result_converter : public iterator_type
{
public:
constexpr iterator_result_converter() = default;
iterator_result_converter(iterator_type &&iter) :
iterator_type(std::move(iter))
{
@ -22,6 +41,10 @@ public:
{
return *this;
}
/* `using iterator_type::operator*()` is not viable here because this
* `operator*()` has a different return type than
* `iterator_type::operator*()`.
*/
result_type operator*() const
{
return this->iterator_type::operator*();
@ -30,6 +53,12 @@ public:
{
return static_cast<iterator_result_converter &>(this->iterator_type::operator++());
}
iterator_result_converter operator++(int)
{
auto r = *this;
this->iterator_type::operator++();
return r;
}
};
template <typename result_type, typename range_type, typename iterator_type = iterator_result_converter<result_type, decltype(std::begin(std::declval<range_type &>()))>>