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Front Page / Algorithms / Transformation Algorithms / replace_if



      typename Sequence
    , typename Pred
    , typename NewType
    , typename In = unspecified
struct replace_if
    typedef unspecified type;


Returns a copy of the original sequence where every type that satisfies the predicate Pred has been replaced with NewType.

[Note: This wording applies to a no-inserter version(s) of the algorithm. See the Expression semantics subsection for a precise specification of the algorithm's details in all cases — end note]


#include <boost/mpl/replace_if.hpp>

Model of

Reversible Algorithm


Parameter Requirement Description
Sequence Forward Sequence An original sequence.
Pred Unary Lambda Expression A replacement condition.
NewType Any type A type to replace with.
In Inserter An inserter.

Expression semantics

The semantics of an expression are defined only where they differ from, or are not defined in Reversible Algorithm.

For any Forward Sequence s, an unary Lambda Expression pred, an Inserter in, and arbitrary type x:

typedef replace_if<s,pred,x,in>::type r;
Return type:

A type.


Equivalent to

typedef lambda<pred>::type p;
typedef transform< s, if_< apply_wrap1<p,_1>,x,_1>, in >::type r;


Linear. Performs exactly size<s>::value applications of pred, and at most size<s>::value insertions.


typedef vector_c<int,1,4,5,2,7,5,3,5> numbers;
typedef vector_c<int,1,4,0,2,0,0,3,0> expected;
typedef replace_if< numbers, greater<_,int_<4> >, int_<0> >::type result;

BOOST_MPL_ASSERT(( equal< result,expected, equal_to<_,_> > ));

See also

Transformation Algorithms, Reversible Algorithm, reverse_replace_if, replace, remove_if, transform