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A comment on Fun with C++26 reflection: Keyword Arguments. Parent comment

Re:Fun with C++26 reflection: Keyword Arguments by drysine on Monday February 17, 2025 @03:33AM (#43076614)
As I stated above, it's the same kind of situation. See my another comment in this thread for an example with designated initializers.

>your code possibly contains undefined behavior

Only if f() returns a pointer to a2 (which is my point). Or did you imply that in the case when f() returns a pointer to a1 and it gets passed to the constructor of a1, provenance matters?

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Re:Fun with C++26 reflection: Keyword Arguments by drysine on Thursday February 20, 2025 @03:34PM (#43119808)
Actually, provenance matters:

"During the construction of an object, if the value of the object or any of its subobjects is accessed through a glvalue that is not obtained, directly or indirectly, from the constructor's this pointer, the value of the object or subobject thus obtained is unspecified." [0]

Reading an unspecified value isn't UB, that's good, but I don't understand why the standard says 'unspecified' because it clearly can be indeterminate if a sub-object hasn't been initialized yet.

[0] https://eel.is/c++draft/class.cdtor#2

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