On 10/22/19 10:53 AM, Marek Polacek wrote:
This patch implements C++20 P0960R3: Parenthesized initialization of aggregates (<wg21.link/p0960>; see R0 for more background info). Essentially, if you have an aggregate, you can now initialize it by (x, y), similarly to {x, y}. E.g.struct A { int x, y; // no A(int, int) ctor (see paren-init14.C for = delete; case) }; A a(1, 2); The difference between ()-init and {}-init is that narrowing conversions are permitted, designators are not permitted, a temporary object bound to a reference does not have its lifetime extended, and there is no brace elision. Further, things like int a[](1, 2, 3); // will deduce the array size const A& r(1, 2.3, 3); // narrowing is OK int (&&rr)[](1, 2, 3); int b[3](1, 2); // b[2] will be value-initialized now work as expected. Note that char f[]("fluff"); has always worked and this patch keeps it that way. Also note that A a((1, 2)) is not the same as A a{{1,2}}; the inner (1, 2) remains a COMPOUND_EXPR. The approach I took was to handle (1, 2) similarly to {1, 2} -- conjure up a CONSTRUCTOR, and introduce LOOKUP_AGGREGATE_PAREN_INIT to distinguish between the two. This kind of initialization is only supported in C++20; I've made no attempt to support it in earlier standards, like we don't support CTAD pre-C++17, for instance.
Could we use a flag on the CONSTRUCTOR to distinguish between them instead, rather than a LOOKUP flag and a flag in the conversion?
Jason
