Each library clause contains the following elements, as applicable:1
Summary
Requirements
Detailed specifications
To save space, items that do not apply to a Clause are omitted. For example, if a Clause does not specify any requirements, there will be no “Requirements” subclause.
The Summary provides a synopsis of the category, and introduces the first-level subclauses. Each subclause also provides a summary, listing the headers specified in the subclause and the library entities provided in each header.
Paragraphs labeled “Note(s):” or “Example(s):” are informative, other paragraphs are normative.
Requirements describe constraints that shall be met by a C++ program that extends the Ranges library. Such extensions are generally one of the following:
Template arguments
Derived classes
Containers, iterators, and algorithms that meet an interface convention or satisfy a concept
Interface convention requirements are stated as generally as possible. Instead of stating “class X has to define a member function operator++(),” the interface requires “for any object x of class X, ++x is defined.” That is, whether the operator is a member is unspecified.
Requirements are stated in terms of concepts (Concepts TS [dcl.spec.concept]). Concepts are stated in terms of well-defined expressions that define valid terms of the types that satisfy the concept. For every set of well-defined expression requirements there is a named concept that specifies an initial set of the valid expressions and their semantics. Any generic algorithm (Clause [algorithms]) that uses the well-defined expression requirements is described in terms of the valid expressions for its formal type parameters.
Template argument requirements are sometimes referenced by name. See ISO/IEC 14882:2014 §[type.descriptions].
In some cases the semantic requirements are presented as C++ code. Such code is intended as a specification of equivalence of a construct to another construct, not necessarily as the way the construct must be implemented.2
Required operations of any concept defined in this document need not be total functions; that is, some arguments to a required operation may result in the required semantics failing to be satisfied. [ Example: The required < operator of the StrictTotallyOrdered concept ([concepts.lib.compare.stricttotallyordered]) does not meet the semantic requirements of that concept when operating on NaNs. — end example ] This does not affect whether a type satisfies the concept.
A declaration may explicitly impose requirements through its associated constraints (Concepts TS [temp.constr.decl]). When the associated constraints refer to a concept (Concepts TS [dcl.spec.concept]), additional semantic requirements are imposed on the use of the declaration.
Although in some cases the code given is unambiguously the optimum implementation.
The detailed specifications of each entity defined in Clauses [concepts.lib]–[numerics] follow the conventions established by ISO/IEC 14882:2014 §[structure.specifications].