This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 113d. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-04-05

837. Constexpr functions and return braced-init-list

[Voted into the WP at the March, 2011 meeting as part of paper N3268.]

The body of a constexpr function is required by 9.2.6 [dcl.constexpr] paragraph 3 to be of the form

{ return expression; }

However, there does not seem to be any good reason for prohibiting the alternate return syntax involving a braced-init-list. The restriction should be removed.

Proposed resolution (March, 2010):

1. Change 8.7.4 [stmt.return] paragraph 2 as follows:

A return statement without an expression with neither an expression nor a braced-init-list can be used only in functions that do not return a value...

2. Change 9.2.6 [dcl.constexpr] paragraph 3 bullets 4 and 5 as follows:

• its function-body shall be a compound-statement of the form

  { return expression ; }

  where expression is a potential constant expression (5.19), or

  { return braced-init-list ; }

  where every assignment-expression that is an initializer-clause appearing directly or indirectly within the braced-init-list is a potential constant expression

• every constructor call and implicit conversion used in converting expression to the function return type initializing the return value (8.7.4 [stmt.return], 9.4 [dcl.init]) shall be one of those allowed in a constant expression (7.7 [expr.const]).

Notes from the March, 2010 meeting:

The new wording added in 7.7 [expr.const] in support of reference parameters for constexpr functions should also be considered to see whether additional changes are needed.