Книга: Standard Template Library Programmer

Function object adaptors

binder1st<AdaptableBinaryFunction>

Categories: functors, adaptors

Component type: type

Binder1st is a function object adaptor: it is used to transform an adaptable binary function into an adaptable unary function. Specifically, if f is an object of class binder1st<AdaptableBinaryFunction>, then f(x) returns F(c, x), where F is an object of class AdaptableBinaryFunction and where c is a constant. Both F and c are passed as arguments to binder1st 's constructor. [1]

The easiest way to create a binder1st is not to call the constructor explicitly, but instead to use the helper function bind1st.

Finds the first nonzero element in a list.

list<int> L;
…
list<int>::iterator first_nonzero = find_if(L.begin(), L.end(), bind1st(not_equal_to<int>(), 0));
assert(first_nonzero == L.end() || *first_nonzero != 0);

Defined in the standard header functional, and in the nonstandard backward-compatibility header function.h.

Adaptable Unary Function

AdaptableBinaryFunction must be a model of Adaptable Binary Function.

unary_function<AdaptableBinaryFunction::second_argument_type, AdaptableBinaryFunction::result_type>

These members are not defined in the Adaptable Unary Function requirements, but are specific to binder1st.

[1] Intuitively, you can think of this operation as "binding" the first argument of a binary function to a constant, thus yielding a unary function. This is a special case of a closure.

The function object overview, binder2nd, Adaptable Unary Function, Adaptable Binary Function

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