[section:merge merge]

[heading Prototype]

``
template<
    class SinglePassRange1,
    class SinglePassRange2,
    class OutputIterator
    >
OutputIterator merge(const SinglePassRange1& rng1,
                     const SinglePassRange2& rng2,
                     OutputIterator          out);

template<
    class SinglePassRange1,
    class SinglePassRange2,
    class OutputIterator,
    class BinaryPredicate
    >
OutputIterator merge(const SinglePassRange1& rng1,
                     const SinglePassRange2& rng2,
                     OutputIterator          out,
                     BinaryPredicate         pred);
``

[heading Description]

`merge` combines two sorted ranges `rng1` and `rng2` into a single sorted range by copying elements. `merge` is stable. The return value is `out + distance(rng1) + distance(rng2)`.

The two versions of `merge` differ by how they compare the elements.

The non-predicate version uses the `operator<()` for the range value type. The predicate version uses the predicate instead of `operator<()`.

[heading Definition]

Defined in the header file `boost/range/algorithm/merge.hpp`

[heading Requirements]

[*For the non-predicate version:]

* `SinglePassRange1` is a model of the __single_pass_range__ Concept.
* `SinglePassRange2` is a model of the __single_pass_range__ Concept.
* `range_value<SinglePassRange1>::type` is the same as `range_value<SinglePassRange2>::type`.
* `range_value<SinglePassRange1>::type` is a model of the `LessThanComparableConcept`.
* The ordering on objects of `range_value<SinglePassRange1>::type` is a [*/strict weak ordering/], as defined in the `LessThanComparableConcept` requirements.
* `range_value<SinglePassRange1>::type` is convertible to a type in `OutputIterator`'s set of value types.

[*For the predicate version:]

* `SinglePassRange1` is a model of the __single_pass_range__ Concept.
* `SinglePassRange2` is a model of the __single_pass_range__ Concept.
* `range_value<SinglePassRange1>::type` is the same as `range_value<SinglePassRange2>::type`.
* `BinaryPredicate` is a model of the `StrictWeakOrderingConcept`.
* `SinglePassRange1`'s value type is convertible to both `BinaryPredicate`'s argument types.
* `range_value<SinglePassRange1>::type` is convertible to a type in `OutputIterator`'s set of value types.

[heading Precondition:]

[heading For the non-predicate version:]

* The elements of `rng1` are in ascending order. That is, for each adjacent element pair `[x,y]` of `rng1`, `y < x == false`.
* The elements of `rng2` are in ascending order. That is, for each adjacent element pair `[x,y]` of `rng2`, `y < x == false`.
* The ranges `rng1` and `[out, out + distance(rng1) + distance(rng2))` do not overlap.
* The ranges `rng2` and `[out, out + distance(rng1) + distance(rng2))` do not overlap.
* `[out, out + distance(rng1) + distance(rng2))` is a valid range.

[heading For the predicate version:]

* The elements of `rng1` are in ascending order. That is, for each adjacent element pair `[x,y]`, of `rng1`, `pred(y, x) == false`.
* The elements of `rng2` are in ascending order. That is, for each adjacent element pair `[x,y]`, of `rng2`, `pred(y, x) == false`.
* The ranges `rng1` and `[out, out + distance(rng1) + distance(rng2))` do not overlap.
* The ranges `rng2` and `[out, out + distance(rng1) + distance(rng2))` do not overlap.
* `[out, out + distance(rng1) + distance(rng2))` is a valid range.

[heading Complexity]

Linear. There are no comparisons if both `rng1` and `rng2` are empty, otherwise at most `distance(rng1) + distance(rng2) - 1` comparisons.

[endsect]