cppdraft_translate/cppdraft/diff/cpp20/expr.md

[diff.cpp20.expr]

Annex C (informative) Compatibility [diff]

C.2 C++ and ISO C++ 2020 [diff.cpp20]

C.2.3 [expr]: expressions [diff.cpp20.expr]

1

#

Affected subclause: [expr.prim.id.unqual]

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.

[Example 1: decltype(auto) f(int&& x) { return (x); } // returns int&&; previously returned int&int& g(int&& x) { return x; } // ill-formed; previously well-formed — end example]

2

#

Affected subclause: [expr.sub]

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.

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