std::experimental::ranges::equal(3)

NAME
std::experimental::ranges::equal - std::experimental::ranges::equal

Synopsis
   Defined in header <experimental/ranges/algorithm>
   template< InputIterator I1, Sentinel<I1> S1, InputIterator I2,
   Sentinel<I2> S2,
   class Pred = ranges::equal_to<>,
   class Proj1 = ranges::identity, class Proj2 = ranges::identity > (1) (ranges TS)
   requires IndirectlyComparable<I1, I2, Pred, Proj1, Proj2>
   bool equal(I1 first1, S1 last1, I2 first2, S2 last2, Pred pred =
   Pred{},
   Proj1 proj1 = Proj1{}, Proj2 proj2 = Proj2{});
   template< InputRange R1, InputRange R2, class Pred =
   ranges::equal_to<>,
   class Proj1 = ranges::identity, class Proj2 = ranges::identity >
   requires IndirectlyComparable<ranges::iterator_t<R1>, (2) (ranges TS)
   ranges::iterator_t<R2>,
   Pred, Proj1, Proj2>
   bool equal(R1&& r1, R2&& r2, Pred pred = Pred{},
   Proj1 proj1 = Proj1{}, Proj2 proj2 = Proj2{});
   template< InputIterator I1, Sentinel<I1> S1, class I2,
   class Pred = ranges::equal_to<>,
   class Proj1 = ranges::identity, class Proj2 = ranges::identity > (ranges TS)
   requires InputIterator<std::decay_t<I2>> && !Range<I2> && (3) (deprecated)
   IndirectlyComparable<I1, std::decay_t<I2>, Pred, Proj1, Proj2>
   bool equal(I1 first1, S1 last1, I2&& first2_, Pred pred = Pred{},
   Proj1 proj1 = Proj1{}, Proj2 proj2 = Proj2{});
   template< InputRange R1, class I2, class Pred = ranges::equal_to<>,
   class Proj1 = ranges::identity, class Proj2 = ranges::identity >
   requires InputIterator<std::decay_t<I2>> && !Range<I2> && (ranges TS)
   IndirectlyComparable<ranges::iterator_t<R1>, std::decay_t<I2>, (4) (deprecated)
   Pred, Proj1, Proj2>
   bool equal(R1&& r1, I2&& first2_, Pred pred = Pred{},
   Proj1 proj1 = Proj1{}, Proj2 proj2 = Proj2{});
   1) Returns true if the range [first1, last1) is equal to the range [first2, last2),
   and false otherwise.
   2) Same as (1), but uses r1 as the first source range and r2 as the second source
   range, as if using ranges::begin(r1) as first1, ranges::end(r1) as last1,
   ranges::begin(r2) as first2, and ranges::end(r2) as last2.
   3) Same as (1), except that the second range is considered to end when either the
   first range is exhausted or the first mismatch is detected. Equivalent to return
   last1 == ranges::mismatch(first1, last1, std::forward<I2>(first2_), comp, proj1,
   proj2).in1();
   4) Same as (3), but uses r1 as the first source range, as if using ranges::begin(r1)
   as first1 and ranges::end(r1) as last1.
   Two ranges are considered equal if they have the same number of elements and, for
   every iterator i in the range [first1,last1), ranges::invoke(pred,
   ranges::invoke(proj1, *i), ranges::invoke(proj2, *(first2 + (i - first1)))) is true.
   Notwithstanding the declarations depicted above, the actual number and order of
   template parameters for algorithm declarations is unspecified. Thus, if explicit
   template arguments are used when calling an algorithm, the program is probably
   non-portable.

Parameters
   first1, last1 - the first range of the elements
   r1 - the first range of the elements
   first2, last2 - the second range of the elements
   r2 - the second range of the elements
   first2_ - the beginning of the second range of the elements
   pred - predicate to apply to the projected elements
   proj1 - projection to apply to the elements in the first range
   proj2 - projection to apply to the elements in the second range

Return value
   true if the two ranges are equal, otherwise returns false.

Notes
   ranges::equal should not be used to compare the ranges formed by the iterators from
   std::unordered_set, std::unordered_multiset, std::unordered_map, or
   std::unordered_multimap because the order in which the elements are stored in those
   containers may be different even if the two containers store the same elements.
   When comparing entire containers for equality, operator== for the corresponding
   container are usually preferred.

Complexity
   1-2) If SizedSentinel<S1, I1> && SizedSentinel<S2, I2> is satisfied and last1 -
   first1 != last2 - first2, no applications of the predicate and projections.
   Otherwise, at most min(last1 - first1, last2 - first2) applications of the predicate
   and each projection.
   3-4) At most last1 - first1 applications of the predicate and each projection.

Possible implementation
   namespace detail
   {
       template< InputIterator I1, SizedSentinel<I1> S1,
                 InputIterator I2, SizedSentinel<I1> S2 >
       bool check_size(I1& first1, S1& last1, I2& first2, S2& last2)
       {
           return last1 - first1 != last2 - first2;
       }
       template< InputIterator I1, Sentinel<I1> S1, InputIterator I2, Sentinel<I1> S2 >
       bool check_size(I1& first1, S1& last1, I2& first2, S2& last2)
       {
           return false;
       }
   }
   template< InputIterator I1, Sentinel<I1> S1, InputIterator I2, Sentinel<I2> S2,
             class Pred = ranges::equal_to<>,
             class Proj1 = ranges::identity, class Proj2 = ranges::identity >
     requires IndirectlyComparable<I1, I2, Pred, Proj1, Proj2>
   bool equal(I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = Pred{},
              Proj1 proj1 = Proj1{}, Proj2 proj2 = Proj2{})
   {
       if(detail::check_size(first1, last1, first2, last2)) return false;
       for(; first1 != last1 && first2 != last2; (void) ++first1, (void)++first2) {
           if(!ranges::invoke(pred, ranges::invoke(proj1, *first1),
                        ranges::invoke(proj2, *first2))) {
               return false;
           }
       }
       return first1 == last1 && first2 == last2;
   }

Example
    This section is incomplete
    Reason: no example

See also
   equal determines if two sets of elements are the same
                        (function template)
   find finds the first element satisfying specific criteria
   find_if (function template)
   find_if_not
                        returns true if one range is lexicographically less than
   lexicographical_compare another
                        (function template)
   mismatch finds the first position where two ranges differ
                        (function template)
   search searches for a range of elements
                        (function template)