C++ named requirements: RangeAdaptorClosureObject (since C++20)
Range adaptor closure objects are FunctionObjects that take one viewable_range (until C++23) range (since C++23) as its only argument and returns a view (until C++23). They are callable via the pipe operator: if C is a range adaptor closure object and R is a viewable_range (until C++23) range (since C++23), these two expressions are equivalent (both well-formed or ill-formed):
C(R) R | C
Two range adaptor closure objects can be chained by operator| to produce another range adaptor closure object: if C and D are range adaptor closure objects, then C | D is also a range adaptor closure object if it is valid.
The bound arguments of C | D is determined as follows:
- there is a subobject in the result object of the same type (cv-qualification discarded) for every subobject in both operands that is a bound argument,
- such a bound argument is direct-non-list-initialized with the source subobject in its containing operand, where the source is identically treated as lvalue or rvalue and cv-qualified to the operand,
- the result is valid if and only if the initialization of all bound arguments are valid.
The effect and validity of the operator() of the result is determined as follows: given a viewable_range (until C++23) range (since C++23) R, these two expressions are equivalent (both well-formed or ill-formed):
R | C | D // (R | C) | D R | (C | D)
Notes: operator() is unsupported for volatile-qualified or const-volatile-qualified version of range adaptor object closure types.
Objects whose type is the same as one of the following objects (ignoring cv-qualification) are range adaptor closure objects:
- unary range adaptor objects,
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(since C++23) |
- the results of binding trailing arguments by range adaptor objects, and
- the results of chaining two range adaptor closure objects by operator|.
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Let |
(since C++23) |
