front

Synopsis

template<
      typename Sequence
    >
struct front
{
    typedef unspecified type;
};

Description

シーケンスの最初の要素と同一の型を返す

Definition

#include "boost/mpl/front.hpp"

Parameters

Parameter	Requirement	Description
`Sequence`	Forward Sequenceのモデル	調べられるシーケンス

Expression semantics

Expression Expression type Precondition Semantics Postcondition

typedef front<Sequence>::type t; 型 empty<Sequence>::type::value == false typedef begin<Sequence>::type::type t;と等価

Expression	Expression type	Precondition	Semantics	Postcondition
`typedef front<Sequence>::type t;`	型	`empty<Sequence>::type::value == false`	`typedef begin<Sequence>::type::type t;と等価`

Complexity

償却定数時間

Example

typedef list<long>::type types1;
typedef list<int,long>::type types2;
typedef list<char,int,long>::type types3;

BOOST_MPL_ASSERT_IS_SAME(front<types1>::type, long);
BOOST_MPL_ASSERT_IS_SAME(front<types2>::type, int);
BOOST_MPL_ASSERT_IS_SAME(front<types3>::type, char);