Shafik Yaghmour

Unclear! Although evidence is it was meant to be well defined, we could justify a few diff positions, see Stack Overflow question Is it defined behavior to reference an early member from a later member expression during aggregate initialization? for some more details.

For C++20 P0329 Designated Initialization if we look at [dcl.init.aggr]p6 it now says:

The initializations of the elements of the aggregate are evaluated in the element order. That is, all value computations and side effects associated with a given element are sequenced before those of any element that follows it in order.

Why can I use foo.i in the declaration? mystruct?

foo{45, foo.i};
————————^

This is covered in [basic.scope.pdecl]p1 says:

The point of declaration for a name is immediately after its complete declarator and before its initializer (if any), except as noted below. [ Example:

unsigned char x = 12;
{ unsigned char x = x; }

Here the second x is initialized with its own (indeterminate) value.— end example]

Which is the source for some interesting questions, for example:

• Does initialization entail lvalue-to-rvalue conversion? Is int x = x; UB?
• Has C++ standard changed with respect to the use of indeterminate values and undefined behavior in C++14?