Standard Template Library Programmer's Guide

Categories: functors, adaptors

Component type: type

Unary_compose is a function object adaptor. If f and g are both Adaptable Unary Functions, and if g 's return type is convertible to f 's argument type, then unary_compose can be used to create a function object h such that h(x) is the same as f(g(x)) . [1] As with other function object adaptors, the easiest way to create a unary_compose is to use the helper function compose1 . It is possible to call unary_compose 's constructor directly, but there is usually no reason to do so.

Calculates the negative of the sines of the elements in a vector, where the elements are angles measured in degrees. Since the C library function sin takes its arguments in radians, this operation is the composition of three operations: negation, sin , and the conversion of degrees to radians.

vector angles;

vector sines;

const double pi = 3.14159265358979323846;

…

assert(sines.size() >= angles.size());

transform(angles.begin(), angles.end(), sines.begin(), compose1(negate(), compose1(ptr_fun(sin), bind2nd(multiplies(), pi / 180.))));

Defined in the standard header functional, and in the nonstandard backward-compatibility header function.h. The unary_compose class is an SGI extension; it is not part of the C++ standard.

Adaptable Unary Function

AdaptableUnaryFunction1 and AdaptableUnaryFunction2 must both be models of Adaptable Unary Function. AdaptableUnaryFunction2::result_type must be convertible to AdaptableUnaryFunction1::argument_type .

unary_function

These members are not defined in the Adaptable Unary Function requirements, but are specific to unary_compose .

[1] This operation is called function composition, hence the name unary_compose . It is often represented in mathematics as the operation f o g , where f o g is a function such that (f o g)(x) == f(g(x)) . Function composition is a very important concept in algebra. It is also extremely important as a method of building software components out of other components, because it makes it possible to construct arbitrarily complicated function objects out of simple ones.

The function object overview, binary_compose , binder1st , binder2nd .

Categories: functors, adaptors

Component type: type

Binary_compose is a function object adaptor. If f is an Adaptable Binary Function and g1 and g2 are both Adaptable Unary Functions, and if g1 's and g2 's return types are convertible to f 's argument types, then binary_compose can be used to create a function object h such that h(x) is the same as f(g1(x), g2(x)) . [1] [2]

Finds the first element in a list that lies in the range from 1 to 10.

list L;

…

list::iterator in_range = find_if(L.begin(), L.end(), compose2(logical_and(), bind2nd(greater_equal(), 1), bind2nd(less_equal(), 10)));

assert(in_range == L.end() || (*in_range >= 1 && *in_range <= 10));

Computes sin(x)/(x + DBL_MIN) for each element of a range.

transform(first, last, first, compose2(divides(), ptr_fun(sin), bind2nd(plus(), DBL_MIN)));

Defined in the standard header functional, and in the nonstandard backward-compatibility header function.h. The binary_compose class is an SGI extension; it is not part of the C++ standard.

Adaptable Unary Function