ISO/IEC TS 19217:2015 Preview

ISO/IEC TS 19217:2015 describes extensions to the C++ Programming Language (1.2) that enable the specification and checking of constraints on template arguments, and the ability to overload functions and specialize class templates based on those constraints. These extensions include new syntactic forms and modifications to existing language semantics.

The International Standard, ISO/IEC 14882, provides important context and specification for this Technical Specification. This document is written as a set of changes against that specification. Instructions to modify or add paragraphs are written as explicit instructions. Modifications made directly to existing text from the International Standard use underlining to represent added text and strikethrough to represent deleted text.

WG21 paper N4191 defines "fold expressions", which are used to define constraint expressions resulting from the use of constrained-parameters that declare template parameter packs. This feature is not present in ISO/IEC 14882:2014, but it is planned to be included in the next revision of that International Standard. The specification of that feature is included in this document.