This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 115e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-11-11

904. Parameter packs in lambda-captures

[Voted into WP at March, 2010 meeting.]

The following is not allowed by the current syntax of lambda-capture but would be useful:

    template <typename ...Args> void f(Args... args) {
      auto l = [&, args...] { return g(args...); };
    }

Proposed resolution (October, 2009):

1. Change the grammar in 7.5.6 [expr.prim.lambda] paragraph 1 as follows:

capture-list:
capture ..._opt
capture-list , capture ..._opt

2. Add a new paragraph at the end of 7.5.6 [expr.prim.lambda]:

A capture followed by an ellipsis is a pack expansion (13.7.4 [temp.variadic]). [Example:

    template<typename ...Args>
    void f(Args... args) {
      auto l = [&, args...] { return g(args...); };
      l();
    }

—end example]

3. Add a new bullet to the list in 13.7.4 [temp.variadic] paragraph 4:

• In a capture-list (7.5.6 [expr.prim.lambda]); the pattern is a capture.

[Editorial note: the editor may wish to consider sorting the bullets in this list in order of section reference.]