Annex C (informative) Compatibility [diff]

Change: Change move-eligible id-expressions from lvalues to xvalues.

Rationale: Simplify the rules for implicit move.

Effect on original feature: Valid C++ 2020 code that relies on a returned id-expression's being an lvalue may change behavior or fail to compile.

For example: decltype(auto) f(int&& x) { return (x); } // returns int&&; previously returned int& int& g(int&& x) { return x; } // ill-formed; previously well-formed

Change: Change the meaning of comma in subscript expressions.

Rationale: Enable repurposing a deprecated syntax to support multidimensional indexing.

Effect on original feature: Valid C++ 2020 code that uses a comma expression within a subscript expression may fail to compile.

For example: arr[1, 2] // was equivalent to arr[(1, 2)], // now equivalent to arr.operator[](1, 2) or ill-formed