This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 117b. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
2025-08-11
1249. Cv-qualification of nested lambda captureSection: 7.5.6.3 [expr.prim.lambda.capture] Status: CD6 Submitter: James Widman Date: 2011-03-02[Accepted as a DR at the October, 2021 meeting.]
Consider the following example:
void f(int i) {
auto l1 = [i] {
auto l2 = [&i] {
++i; // Well-formed?
};
};
}
Because the l1 lambda is not marked as mutable, its operator() is const; however, it is not clear from the wording of 7.5.6 [expr.prim.lambda] paragraph 16 whether the captured member of the enclosing lambda is considered const or not.
Proposed resolution (August, 2021):
Change 7.5.6.3 [expr.prim.lambda.capture] paragraph 14 as follows:
If a lambda-expression m2 captures an entity and that entity is captured by an immediately enclosing lambda-expression m1, then m2's capture is transformed as follows:
if Ifm1 captures the entity by copy, m2 captures the corresponding non-static data member of m1's closure type; if m1 is not mutable, the non-static data member is considered to be const-qualified.
if Ifm1 captures the entity by reference, m2 captures the same entity captured by m1.
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