C++ named requirements: RangeAdaptorClosureObject (since C++20)

Range adaptor closure objects are FunctionObject s that are callable via the pipe operator: if C is a range adaptor closure object and R is a range , these two expressions are equivalent :

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 produces a range adaptor closure object E with the following properties:

• E stores a copy of C and D , direct-non-list-initialized from std:: forward < decltype ( ( C ) ) > ( C ) and std:: forward < decltype ( ( D ) ) > ( D ) respectively. If such initialization is invalid, C | D is also invalid.
• Let c and d be the stored copies (with the same constness and value category as E ), and R be a range object, the following expressions are equivalent :

d(c(R))
R | c | d
E(R)
R | E // 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,

• the results of binding trailing arguments by range adaptor objects, and
• the results of chaining two range adaptor closure objects by operator | .

See also