source:
downloads/boost_1_34_1/libs/mpl/doc/src/refmanual/front.rst
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front
Synopsis
template<
typename Sequence
>
struct front
{
typedef |unspecified| type;
};
Description
Returns the first element in the sequence.
Header
#include <boost/mpl/front.hpp>
Model of
Parameters
| Parameter | Requirement | Description |
|---|---|---|
| Sequence | |Forward Sequence| | A sequence to be examined. |
Expression semantics
For any |Forward Sequence| s:
typedef front<s>::type t;
| Return type: | A type. |
|---|---|
| Precondition: | empty<s>::value == false. |
| Semantics: | Equivalent to typedef deref< begin<s>::type >::type t; |
Complexity
Amortized constant time.
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> ));
See also
|Forward Sequence|, |back|, |push_front|, |begin|, |deref|, |at|
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