# `order_statistics_key_cmp` Interface

A comparison functor. Transforms any comparison functor operating on logical keys to a comparison functor operating on order statistics keys.

1. `order_statistics_key.hpp`
2. Template parameters.
3. Base classes.
4. Public Types and Constants:
   1. Policy definitions.
   2. Key-type definitions.
5. Public Methods:
   1. Constructors, destructor, and related.
   2. Operators.
   3. Policy access methods.

## Template parameters.

Parameter | Description | Default Value

    Cmp_Fn

Comparison functor.

    std::less<Key>

    Allocator

Allocator type.

The allocator is only used for definitions, e.g., size_type, pointer, and reference.

    std::allocator<char>

## Base classes.

Class | Derivation Type

    std::binary_function<
      order_statistics_key<
        typename Cmp_Fn::first_argument_type, Allocator>,
      order_statistics_key<
        typename Cmp_Fn::second_argument_type, Allocator>,
      bool>

public

## Policy definitions.

Type | Definition | Description

    allocator

    Allocator

Allocator type.

    cmp_fn

    Cmp_Fn

Comparison functor type.

## Key-type definitions.

Type | Definition | Description

    key_type

    order_statistics_key<
        typename Cmp_Fn::first_argument_type, Allocator>

Key type.

    const_key_reference

    typename allocator::template rebind<
        key_type>::other::const_reference

Const key reference type.

## Constructors, destructor, and related.

Method | Description

    inline
      order_statistics_key_cmp
      ()

Default constructor.

    inline
      order_statistics_key_cmp
      (const Cmp_Fn &r_cmp_fn)

Constructor taking a comparison functor.

## Operators.

Method | Description

    inline bool
      operator()
      (const_key_reference r_lhs_key,
        const_key_reference r_rhs_key) const

Compares two keys.

## Policy access methods.

Method | Description

    inline cmp_fn &
      get_cmp_fn
      ()

Access to the comparison functor object used.

    inline const cmp_fn &
      get_cmp_fn
      () const

Const access to the comparison functor object used.