unary_compose<AdaptableUnaryFunction1,AdaptableUnaryFunction2>



Categories: functors, adaptors	Component type: type

Description

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.

Example

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<double> angles;
vector<double> sines;
const double pi = 3.14159265358979323846;
...
assert(sines.size() >= angles.size());
transform(angles.begin(), angles.end(), sines.begin(),
          compose1(negate<double>(),
                   compose1(ptr_fun(sin),
                            bind2nd(multiplies<double>(), pi / 180.))));

Definition

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.

Template parameters

Parameter	Description	Default
`AdaptableUnaryFunction1`	The type of the first operand in the function composition operation. That is, if the composition is written `f o g` [1], then `AdaptableUnaryFunction1` is the type of the function object `f`.
`AdaptableUnaryFunction2`	The type of the second operand in the function composition operation. That is, if the composition is written `f o g` [1], then `AdaptableUnaryFunction2` is the type of the function object `g`.

Model of

Adaptable Unary Function

Type requirements

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

Public base classes

unary_function<AdaptableUnaryFunction2::argument_type,
               AdaptableUnaryFunction1::result_type>

Members

Member	Where defined	Description
`argument_type`	Adaptable Unary Function	The type of the function object's argument: `AdaptableUnaryFunction2::argument_type`.
`result_type`	Adaptable Unary Function	The type of the result: `AdaptableUnaryFunction1::result_type`
unary_compose(const AdaptableUnaryFunction1& f, const AdaptableUnaryFunction2& g);	`unary_compose`	See below.
template <class AdaptableUnaryFunction1, class AdaptableUnaryFunction2> unary_compose<AdaptableUnaryFunction1, AdaptableUnaryFunction2> compose1(const AdaptableUnaryFunction1& op1, const AdaptableUnaryFunction2& op2);	`unary_compose`	See below.

New members

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

Member	Description
unary_compose(const AdaptableUnaryFunction1& f, const AdaptableUnaryFunction2& g);	The constructor. Constructs a `unary_compose` object that represents the function object `f o g`. [1]
template <class AdaptableUnaryFunction1, class AdaptableUnaryFunction2> unary_compose<AdaptableUnaryFunction1, AdaptableUnaryFunction2> compose1(const AdaptableUnaryFunction1& op1, const AdaptableUnaryFunction2& op2);	Creates a `unary_compose` object. If `f` and `g` are, respectively, of classes `AdaptableUnaryFunction1` and `AdaptableUnaryFunction2`, then `compose1(f, g)` is equivalent to `unary_compose<AdaptableUnaryFunction1, AdaptableUnaryFunction2>(f, g)`, but is more convenient. This is a global function, not a member function.

Notes

[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.