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Difference between revisions of "cpp/algorithm/ranges/contains"

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< cpp‎ | algorithm‎ | ranges
m (→Notes: fmt; →See also: ++)
m (→‎Possible implementation: +)
Line 71: Line 71:
  
 
{{feature test macro|__cpp_lib_ranges_contains}}
 
{{feature test macro|__cpp_lib_ranges_contains}}
 +
 +
=== Possible implementation ===
 +
{{eq fun
 +
| 1=
 +
struct __contains_fn
 +
{
 +
    template< std::input_iterator I, std::sentinel_for<I> S,
 +
              class T, class Proj = std::identity >
 +
    requires std::indirect_binary_predicate<ranges::equal_to, std::projected<I, Proj>,
 +
                                            const T*>
 +
    constexpr bool operator()(I first, S last, const T& value, Proj proj = {}) const
 +
    {
 +
        return ranges::find(std::move(first), last, value, proj) != last;
 +
    }
 +
 +
    template< ranges::input_range R, class T, class Proj = std::identity >
 +
    requires std::indirect_binary_predicate<ranges::equal_to,
 +
                                            std::projected<ranges::iterator_t<R>, Proj>,
 +
                                            const T*>
 +
    constexpr bool operator()(R&& r, const T& value, Proj proj = {}) const
 +
    {
 +
        return (*this)(ranges::begin(r), ranges::end(r), std::move(value), proj);
 +
    }
 +
};
 +
 +
inline constexpr __contains_fn contains {};
 +
| 2=
 +
struct __contains_subrange_fn
 +
{
 +
    template< std::forward_iterator I1, std::sentinel_for<I1> S1,
 +
              std::forward_iterator I2, std::sentinel_for<I2> S2,
 +
              class Pred = ranges::equal_to,
 +
              class Proj1 = std::identity, class Proj2 = std::identity >
 +
    requires std::indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
 +
    constexpr bool operator()(I1 first1, S1 last1,
 +
                              I2 first2, S2 last2,
 +
                              Pred pred = {},
 +
                              Proj1 proj1 = {}, Proj2 proj2 = {}) const
 +
    {
 +
        return (first2 == last2) {{!!}}
 +
              !ranges::search(first1, last1, first2, last2, pred, proj1, proj2).empty();
 +
    }
 +
 +
    template< ranges::forward_range R1, ranges::forward_range R2,
 +
              class Pred = ranges::equal_to,
 +
              class Proj1 = std::identity, class Proj2 = std::identity >
 +
    requires std::indirectly_comparable<ranges::iterator_t<R1>,
 +
                                        ranges::iterator_t<R2>, Pred, Proj1, Proj2>
 +
    constexpr bool operator()(R1&& r1, R2&& r2,
 +
                              Pred pred = {},
 +
                              Proj1 proj1 = {}, Proj2 proj2 = {}) const
 +
    {
 +
        return (*this)(ranges::begin(r1), ranges::end(r1),
 +
                      ranges::begin(r2), ranges::end(r2), std::move(pred),
 +
                      std::move(proj1), std::move(proj2));
 +
    }
 +
};
 +
 +
inline constexpr __contains_subrange_fn contains_subrange {};
 +
}}
  
 
=== Example ===
 
=== Example ===

Revision as of 03:51, 29 July 2022

 
C++
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
(C++17)
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
(C++11)
(C++11)
(C++11)
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
(C++20)(C++20)
Sampling operations
(C++17)

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
(C++11)
(C++17)
Lexicographical comparison operations
(C++20)
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
 
Constrained algorithms
All names in this menu belong to namespace std::ranges
Non-modifying sequence operations
Modifying sequence operations
Partitioning operations
Sorting operations
Binary search operations (on sorted ranges)
       
       
    
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations
       
       
Permutation operations
Fold operations
Numeric operations
(C++23)            
Operations on uninitialized storage
Return types
 
Defined in header <algorithm>
Call signature
template< std::input_iterator I, std::sentinel_for<I> S,

          class T, class Proj = std::identity >
requires std::indirect_binary_predicate<ranges::equal_to, std::projected<I, Proj>,
                                        const T*>

constexpr bool contains( I first, S last, const T& value, Proj proj = {} );
 (1) (since C++23)
template< ranges::input_range R, class T, class Proj = std::identity >

requires std::indirect_binary_predicate<ranges::equal_to,
                                        std::projected<ranges::iterator_t<R>, Proj>,
                                        const T*>

constexpr bool contains( R&& r, const T& value, Proj proj = {} );
 (2) (since C++23)
template< std::forward_iterator I1, std::sentinel_for<I1> S1,

          std::forward_iterator I2, std::sentinel_for<I2> S2,
          class Pred = ranges::equal_to,
          class Proj1 = std::identity, class Proj2 = std::identity >
requires std::indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
constexpr bool contains_subrange( I1 first1, S1 last1,
                                  I2 first2, S2 last2,
                                  Pred pred = {},

                                  Proj1 proj1 = {}, Proj2 proj2 = {} );
 (3) (since C++23)
template< ranges::forward_range R1, ranges::forward_range R2,

          class Pred = ranges::equal_to,
          class Proj1 = std::identity, class Proj2 = std::identity >
requires std::indirectly_comparable<ranges::iterator_t<R1>,
                                    ranges::iterator_t<R2>, Pred, Proj1, Proj2>
constexpr bool contains_subrange( R1&& r1, R2&& r2,
                                  Pred pred = {},

                                  Proj1 proj1 = {}, Proj2 proj2 = {} );
 (4) (since C++23)
1) Search-based algorithm that checks whether or not a given range contains a value with iterator-sentinel pairs.
2) Same as (1) but uses r as the source range, as if using ranges::begin(r) as first and ranges::end(r) as last.
3) Search-based algorithm that checks whether or not a given range is a subrange of another range with iterator-sentinel pairs.
4) Same as (3) 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.

The function-like entities described on this page are niebloids, that is:

In practice, they may be implemented as function objects, or with special compiler extensions.

Contents

Parameters

first, last - the range of elements to examine
r - the range of the elements to examine
value - value to compare the elements to
pred - predicate to apply to the projected elements
proj - projection to apply to the elements

Return value

1-2) : ranges::find(std::move(first), last, value, proj) != last
3-4) : first2 == last2 || !ranges::search(first1, last1, first2, last2, pred, proj1, proj2).empty()

Complexity

At most last - first applications of the predicate and projection.

Notes

Up until C++20, we've had to write std::ranges::find(r, value) != std::ranges::end(r) to determine if a single value is inside a range. And to check if a range contains a subrange of interest, we use not std::ranges::search(haystack, needle).empty(). While this is accurate, it isn't necessarily convenient, and it hardly expresses intent (especially in the latter case). Being able to say std::ranges::contains(r, value) addresses both of these points. Further evidence for the existence of a contains algorithm is that the STL gave C++98 an obscurely-named contains algorithm called binary_search, and any_of is "contains with a predicate", showing that there's prior art for this contains to be an algorithm.

ranges::contains_subrange, same as ranges::search, but as opposed to std::search, provides no access to Searchers (such as Boyer-Moore).

Feature-test macro Value Std Feature
__cpp_lib_ranges_contains  

Possible implementation

First version 
struct __contains_fn
{
    template< std::input_iterator I, std::sentinel_for<I> S,
              class T, class Proj = std::identity >
    requires std::indirect_binary_predicate<ranges::equal_to, std::projected<I, Proj>, 
                                            const T*>
    constexpr bool operator()(I first, S last, const T& value, Proj proj = {}) const
    {
        return ranges::find(std::move(first), last, value, proj) != last;
    }
 
    template< ranges::input_range R, class T, class Proj = std::identity >
    requires std::indirect_binary_predicate<ranges::equal_to,
                                            std::projected<ranges::iterator_t<R>, Proj>,
                                            const T*>
    constexpr bool operator()(R&& r, const T& value, Proj proj = {}) const
    {
        return (*this)(ranges::begin(r), ranges::end(r), std::move(value), proj);
    }
};
 
inline constexpr __contains_fn contains {};
Second version 
struct __contains_subrange_fn
{
    template< std::forward_iterator I1, std::sentinel_for<I1> S1,
              std::forward_iterator I2, std::sentinel_for<I2> S2,
              class Pred = ranges::equal_to,
              class Proj1 = std::identity, class Proj2 = std::identity >
    requires std::indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
    constexpr bool operator()(I1 first1, S1 last1,
                              I2 first2, S2 last2,
                              Pred pred = {},
                              Proj1 proj1 = {}, Proj2 proj2 = {}) const
    {
        return (first2 == last2) ||
               !ranges::search(first1, last1, first2, last2, pred, proj1, proj2).empty();
    }
 
    template< ranges::forward_range R1, ranges::forward_range R2,
              class Pred = ranges::equal_to,
              class Proj1 = std::identity, class Proj2 = std::identity >
    requires std::indirectly_comparable<ranges::iterator_t<R1>, 
                                        ranges::iterator_t<R2>, Pred, Proj1, Proj2>
    constexpr bool operator()(R1&& r1, R2&& r2,
                              Pred pred = {},
                              Proj1 proj1 = {}, Proj2 proj2 = {}) const
    {
        return (*this)(ranges::begin(r1), ranges::end(r1),
                       ranges::begin(r2), ranges::end(r2), std::move(pred),
                       std::move(proj1), std::move(proj2));
    }
};
 
inline constexpr __contains_subrange_fn contains_subrange {};

Example

This section is incomplete
Reason: example

See also

(C++20)(C++20)(C++20)
 finds the first element satisfying specific criteria
(niebloid)[edit]
(C++20)
 searches for the first occurrence of a range of elements
(niebloid)[edit]
(C++20)
 determines if an element exists in a partially-ordered range
(niebloid)[edit]
(C++20)(C++20)(C++20)
 checks if a predicate is true for all, any or none of the elements in a range
(niebloid)[edit]
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