Note: This paper was adopted into draft C++14 on Saturday at the Bristol UK ISO C++ meeting.

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Document number: N3649

Date: 2013-04-19

Generic (Polymorphic) Lambda Expressions (Revision 3)

by Faisal Vali, Herb Sutter, Dave Abrahams

Excerpt:

This document revises wording for generic lambda expressions as described in N3559: Proposal for Generic (Polymorphic) Lambda Expressions (Revision 2) and as approved by EWG and which should be referenced for further detail.  Today’s C++11 lambda expression concisely creates an instance of a class having a non-template function call operator.  We propose a pure extension of C++11 lambda syntax that creates an instance of a class having a function call operator template. 

Here follow some examples of the proposed syntax extension in use:

// 'Identity' is a lambda that accepts an argument of any type and
// returns the value of its parameter. 
auto Identity = [](auto a) { return a; };
int three = Identity(3);
char const* hello = Identity("hello");

// Conversion to function pointer for capture-less lambdas
int (*fpi)(int) = Identity;
char (*fpc)(char) = Identity;