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| Categories: functors, adaptors | Component type: type |
Description
Binary_compose is a functors adaptor. If f is an AdaptableBinaryFunction and g1 and g2 are both AdaptableUnaryFunction, 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]
Example
Finds the first element in a list that lies in the range from 1 to 10.
List<int> L;
...
List<int>::iterator in_range =
find_if(L.begin(), L.end(),
compose2(logical_and<bool>(),
bind2nd(greater_equal<int>(), 1),
bind2nd(less_equal<int>(), 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<double>(),
ptr_fun(sin),
bind2nd(plus<double>(), DBL_MIN)));
Definition
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.
Template parameters
| Parameter | Description | Default |
AdaptableBinaryFunction | The type of the "outer" function in the function composition operation. That is, if the binary_compose is a function object h such that h(x) = f(g1(x), g2(x)), then AdaptableBinaryFunction is the type of f. | |
AdaptableUnaryFunction1 | The type of the first "inner" function in the function composition operation. That is, if the binary_compose is a function object h such that h(x) = f(g1(x), g2(x)), then AdaptableBinaryFunction is the type of g1. | |
AdaptableUnaryFunction2 | The type of the second "inner" function in the function composition operation. That is, if the binary_compose is a function object h such that h(x) = f(g1(x), g2(x)), then AdaptableBinaryFunction is the type of g2. | |
Model of
AdaptableUnaryFunction
Type requirements
AdaptableBinaryFunction must be a model of AdaptableBinaryFunction. AdaptableUnaryFunction1 and AdaptableUnaryFunction2 must both be models of AdaptableUnaryFunction. The argument types of AdaptableUnaryFunction1 and AdaptableUnaryFunction2 must be convertible to each other. The result types of AdaptableUnaryFunction1 and AdaptableUnaryFunction2 must be convertible, respectively, to the first and second argument types of AdaptableBinaryFunction.
Public base classes
unary_function<AdaptableUnaryFunction1::argument_type,
AdaptableBinaryFunction::result_type>
Members
| Member | Where defined | Description |
argument_type | AdaptableUnaryFunction | The type of the function object's argument: AdaptableUnaryFunction::argument_type. |
result_type | AdaptableUnaryFunction | The type of the result: AdaptableBinaryFunction::result_type |
binary_compose(const AdaptableBinaryFunction& f,
const AdaptableUnaryFunction1& g1,
const AdaptableUnaryFunction1& g2);
| binary_compose | See below. |
template <class AdaptableBinaryFunction,
class AdaptableUnaryFunction1,
class AdaptableUnaryFunction2>
binary_compose<AdaptableBinaryFunction,
AdaptableUnaryFunction1,
AdaptableUnaryFunction2>
compose2(const AdaptableBinaryFunction&,
const AdaptableUnaryFunction1&,
const AdaptableUnaryFunction2&);
| binary_compose | See below. |
New members
These members are not defined in the AdaptableUnaryFunction requirements, but are specific to binary_compose.
| Member | Description |
binary_compose(const AdaptableBinaryFunction& f,
const AdaptableUnaryFunction1& g1,
const AdaptableUnaryFunction1& g2);
| The constructor. Constructs a binary_compose object such that calling that object with the argument x returns f(g1(x), g2(x)). |
template <class AdaptableBinaryFunction,
class AdaptableUnaryFunction1,
class AdaptableUnaryFunction2>
binary_compose<AdaptableBinaryFunction,
AdaptableUnaryFunction1,
AdaptableUnaryFunction2>
compose2(const AdaptableBinaryFunction&,
const AdaptableUnaryFunction1&,
const AdaptableUnaryFunction2&);
| Creates a binary_compose object. If f, g, and g2 are, respectively, of classes AdaptableBinaryFunction, AdaptableUnaryFunction1, and AdaptableUnaryFunction2, then compose2(f, g1, g2) is equivalent to binary_compose<AdaptableBinaryFunction, AdaptableUnaryFunction1, AdaptableUnaryFunction2>(f, g1, g2), but is more convenient. This is a global function, not a member function. |
Notes
[1] This is a form of function composition. The unary_compose adaptor allows composition of AdaptableUnaryFunction; note, however, that once binary functions are introduced, there are several possible patterns of function composition. The binary_compose allows you to form a unary function by putting together two unary functions and a binary function, but you could also, for example, imagine putting together two unary functions and a binary function to form a binary function. In that case, f, g1, and g2 would be combined into a function object h such that h(x,y) = f(g1(x), g2(y)).
See also
The functors, unary_compose, binder1st, binder2nd.
