## unary_compose

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
`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 AdaptableUnaryFunction1 is the type of the function object g.

### 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.