|
|
|
|
| |
| Categories: functors, adaptors | Component type: type |
Description
Unary_compose is a functors adaptor. If f and g are both AdaptableUnaryFunction, 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(times<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 AdaptableUnaryFunction1 is the type of the function object g. | |
Model of
AdaptableUnaryFunction
Type requirements
AdaptableUnaryFunction1 and AdaptableUnaryFunction2 must both be models of AdaptableUnaryFunction. 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 | AdaptableUnaryFunction | The type of the function object's argument: AdaptableUnaryFunction2::argument_type. |
result_type | AdaptableUnaryFunction | 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 AdaptableUnaryFunction 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.
See also
The functors, binary_compose, binder1st, binder2nd.
