https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91363
--- Comment #5 from Marek Polacek ---
Author: mpolacek
Date: Tue Dec 3 15:59:40 2019
New Revision: 278939
URL: https://gcc.gnu.org/viewcvs?rev=278939=gcc=rev
Log:
PR c++/91363 - P0960R3: Parenthesized initialization of aggregates.
This patch implements C++20 P0960R3: Parenthesized initialization of aggregates
(; 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 (&)[](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.
* c-cppbuiltin.c (c_cpp_builtins): Predefine
__cpp_aggregate_paren_init=201902 for -std=c++2a.
* call.c (build_new_method_call_1): Handle parenthesized initialization
of aggregates by building up a CONSTRUCTOR.
(extend_ref_init_temps): Do nothing for CONSTRUCTOR_IS_PAREN_INIT.
* cp-tree.h (CONSTRUCTOR_IS_PAREN_INIT, LOOKUP_AGGREGATE_PAREN_INIT):
Define.
* decl.c (grok_reference_init): Handle aggregate initialization from
a parenthesized list of values.
(reshape_init): Do nothing for CONSTRUCTOR_IS_PAREN_INIT.
(check_initializer): Handle initialization of an array from a
parenthesized list of values. Use NULL_TREE instead of NULL.
* tree.c (build_cplus_new): Handle BRACE_ENCLOSED_INITIALIZER_P.
* typeck2.c (digest_init_r): Set LOOKUP_AGGREGATE_PAREN_INIT if it
receives a CONSTRUCTOR with CONSTRUCTOR_IS_PAREN_INIT set. Allow
narrowing when LOOKUP_AGGREGATE_PAREN_INIT.
(massage_init_elt): Don't lose LOOKUP_AGGREGATE_PAREN_INIT when passing
flags to digest_init_r.
* g++.dg/cpp0x/constexpr-99.C: Only expect an error in C++17 and
lesser.
* g++.dg/cpp0x/explicit7.C: Likewise.
* g++.dg/cpp0x/initlist12.C: Adjust dg-error.
* g++.dg/cpp0x/pr31437.C: Likewise.
* g++.dg/cpp2a/feat-cxx2a.C: Add __cpp_aggregate_paren_init test.
* g++.dg/cpp2a/paren-init1.C: New test.
* g++.dg/cpp2a/paren-init10.C: New test.
* g++.dg/cpp2a/paren-init11.C: New test.
* g++.dg/cpp2a/paren-init12.C: New test.
* g++.dg/cpp2a/paren-init13.C: New test.
* g++.dg/cpp2a/paren-init14.C: New test.
* g++.dg/cpp2a/paren-init15.C: New test.
* g++.dg/cpp2a/paren-init16.C: New test.
* g++.dg/cpp2a/paren-init17.C: New test.
* g++.dg/cpp2a/paren-init18.C: New test.
* g++.dg/cpp2a/paren-init19.C: New test.
* g++.dg/cpp2a/paren-init2.C: New test.
* g++.dg/cpp2a/paren-init3.C: New test.
* g++.dg/cpp2a/paren-init4.C: New test.
* g++.dg/cpp2a/paren-init5.C: New test.
* g++.dg/cpp2a/paren-init6.C: New test.
* g++.dg/cpp2a/paren-init7.C: New test.
* g++.dg/cpp2a/paren-init8.C: New test.
* g++.dg/cpp2a/paren-init9.C: New test.
* g++.dg/ext/desig10.C: Adjust dg-error.
* g++.dg/template/crash107.C: Likewise.
* g++.dg/template/crash95.C: Likewise.
* g++.old-deja/g++.jason/crash3.C: Likewise.
* g++.old-deja/g++.law/ctors11.C: Likewise.
* g++.old-deja/g++.law/ctors9.C: Likewise.
* g++.old-deja/g++.mike/net22.C: Likewise.
* g++.old-deja/g++.niklas/t128.C: Likewise.
Added:
trunk/gcc/testsuite/g++.dg/cpp2a/paren-init1.C
trunk/gcc/testsuite/g++.dg/cpp2a/paren-init10.C
trunk/gcc/testsuite/g++.dg/cpp2a/paren-init11.C
trunk/gcc/testsuite/g++.dg/cpp2a/paren-init12.C
trunk/gcc/testsuite/g++.dg/cpp2a/paren-init13.C
trunk/gcc/testsuite/g++.dg/cpp2a/paren-init14.C
trunk/gcc/testsuite/g++.dg/cpp2a/paren-init15.C
trunk/gcc/testsuite/g++.dg/cpp2a/paren-init16.C
trunk/gcc/testsuite/g++.dg/cpp2a/paren-init17.C
trunk/gcc/testsuite/g++.dg/cpp2a/paren-init18.C
trunk/gcc/testsuite/g++.dg/cpp2a/paren-init19.C
trunk/gcc/testsuite/g++.dg/cpp2a/paren-init2.C
