Intel Threading Building Blocks

Pseudosignatures in Generic Programming

Two approaches for defining Concepts are valid expressions and pseudosignatures. The C++ standard follows the valid expressions approach that shows what the usage pattern looks like for a Concept. It has the drawback of relegating important details to notational conventions. This document uses pseudosignatures because they are concise and can be cut-and-pasted for an initial implementation.

You can find information on where to learn more about pseudosignatures versus valid expressions in the paper by Siek et al. in the “Further Reading” section of this chapter. Table 12-1 shows pseudosignatures for a Sortable type T.

Table 12-1. Pseudosignatures for example Sortable Concept

Pseudosignature	Semantics
bool operator<(const T& x, const T& y)	Compare x and y.
void swap(T& x, T& y)	Swap x and y.

A real signature may differ from the pseudosignature by relying on implicit conversions allowed by C++ to deal with the difference. For an example, type U, the real signature that implements operator< in Table 12-1, can be expressed as int operator<( U x, U y ) because C++ permits implicit conversion from int to bool and implicit conversion from U to (constU&). Similarly, the real signature bool operator <( U&x,U&y ) is acceptable because C++ permits implicit addition of a const qualifier to a reference type.