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c++: Implement C++26 P0963R3 - Structured binding declaration as a condition [PR115745]

Browse source 
This C++26 paper allows structured bindings declaration in
if/while/for/switch conditions, where the structured binding shouldn't
be initialized by array (so in the standard only non-union class types;
as extension _Complex will also work and vectors will be diagnosed because
of conversion issues) and the decision variable is the artificial variable
(e in the standard) itself contextually converted to bool or converted to
some integer/enumeration type.
The standard requires that the conversion is evaluated before the get calls
in case of std::tuple* using class, so the largest part of the patch is making
sure this can be done during instantiation without duplicating too much
code.
In cp_parser_condition, creating a TARGET_EXPR to hold temporarily the
bool or int/enum result of the conversion across the get calls is easy, it
could be just added in between cp_finish_decl and cp_finish_decomp, but for
pt.cc there was no easy spot to add that.
In the end, the patch uses DECL_DECOMP_BASE for this.  That tree is used
primarily for the user vars or var proxies to point back at the
DECL_ARTIFICIAL e variable, before this patch it has been NULL_TREE on
the base.  In some places code was checking if DECL_DECOMP_BASE is NULL_TREE
to find out if it is the base or user var/var proxy.
The patch introduces DECL_DECOMP_IS_BASE macro for what used to be
!DECL_DECOMP_BASE and can stick something else in the base's
DECL_DECOMP_BASE as long as it is not a VAR_DECL.
The patch uses integer_zero_node to mark if/while/for condition structured
binding, integer_one_node to mark switch condition structured binding and
finally cp_finish_decomp sets it to TARGET_EXPR if some get method calls are
emitted and from there the callers can pick that up.  This way I also
avoided code duplication between !processing_template_decl parsing and
pt.cc.

2024-07-02  Jakub Jelinek  <jakub@redhat.com>

	PR c++/115745
gcc/cp/
	* cp-tree.h: Implement C++26 P0963R3 - Structured binding declaration
	as a condition.
	(DECL_DECOMP_BASE): Adjust comment.
	(DECL_DECOMP_IS_BASE): Define.
	* parser.cc (cp_parser_selection_statement): Adjust
	cp_parser_condition caller.
	(cp_parser_condition): Add KEYWORD argument.  Parse
	C++26 structured bindings in conditions.
	(cp_parser_c_for, cp_parser_iteration_statement): Adjust
	cp_parser_condition callers.
	(cp_parser_simple_declaration): Adjust
	cp_parser_decomposition_declaration caller.
	(cp_parser_decomposition_declaration): Add KEYWORD argument.
	If it is not RID_MAX, diagnose for C++23 and older rather than C++14
	and older.  Set DECL_DECOMP_BASE to integer_zero_node for structured
	bindings used in if/while/for conditions or integer_one_node for
	those used in switch conditions.
	* decl.cc (poplevel, check_array_initializer): Use DECL_DECOMP_IS_BASE
	instead of !DECL_DECOMP_BASE.
	(cp_finish_decomp): Diagnose array initializer for structured bindings
	used in conditions.  If using std::tuple_{size,element}, emit
	conversion to bool or integer/enumeration of e into a TARGET_EXPR
	before emitting get method calls.
	* decl2.cc (mark_used): Use DECL_DECOMP_IS_BASE instead of
	!DECL_DECOMP_BASE.
	* module.cc (trees_in::tree_node): Likewise.
	* typeck.cc (maybe_warn_about_returning_address_of_local): Likewise.
	* semantics.cc (maybe_convert_cond): For structured bindings with
	TARGET_EXPR DECL_DECOMP_BASE use that as condition.
	(finish_switch_cond): Likewise.
gcc/testsuite/
	* g++.dg/cpp1z/decomp16.C: Adjust expected diagnostics.
	* g++.dg/cpp26/decomp3.C: New test.
	* g++.dg/cpp26/decomp4.C: New test.
	* g++.dg/cpp26/decomp5.C: New test.
	* g++.dg/cpp26/decomp6.C: New test.
	* g++.dg/cpp26/decomp7.C: New test.
	* g++.dg/cpp26/decomp8.C: New test.
	* g++.dg/cpp26/decomp9.C: New test.
	* g++.dg/cpp26/decomp10.C: New test.
This commit is contained in:
Jakub Jelinek 2024-07-02 22:07:30 +02:00
parent cc63b59e88
commit f30bdb1f2d
16 changed files with 927 additions and 27 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

10
gcc/cp/cp-tree.h
View file

@ -4472,10 +4472,18 @@ get_vec_init_expr (tree t)
? DECL_LANG_SPECIFIC (NODE)->u.base.selector == lds_decomp \
: false)
/* The underlying artificial VAR_DECL for structured binding. */
/* The underlying artificial VAR_DECL for structured binding. On the
artificial base VAR_DECL this can be NULL, or integer_{zero,one}_node
for structured binding used in if/while/for resp. switch conditions,
or a TARGET_EXPR with the condition value after cp_finish_decomp in
those cases. */
#define DECL_DECOMP_BASE(NODE) \
(LANG_DECL_DECOMP_CHECK (NODE)->base)
/* True for the artificial VAR_DECL for structured binding. */
#define DECL_DECOMP_IS_BASE(NODE) \
(!DECL_DECOMP_BASE (NODE) || !VAR_P (DECL_DECOMP_BASE (NODE)))
/* Nonzero if NODE is an inline VAR_DECL. In C++17, static data members
declared with constexpr specifier are implicitly inline variables. */
#define DECL_INLINE_VAR_P(NODE) \

34
gcc/cp/decl.cc
View file

@ -710,7 +710,7 @@ poplevel (int keep, int reverse, int functionbody)
&& ! DECL_IN_SYSTEM_HEADER (decl)
/* For structured bindings, consider only real variables, not
subobjects. */
&& (DECL_DECOMPOSITION_P (decl) ? !DECL_DECOMP_BASE (decl)
&& (DECL_DECOMPOSITION_P (decl) ? DECL_DECOMP_IS_BASE (decl)
: (DECL_NAME (decl) && !DECL_ARTIFICIAL (decl)))
/* Don't warn about name-independent declarations. */
&& !name_independent_decl_p (decl)
@ -7573,7 +7573,7 @@ check_array_initializer (tree decl, tree type, tree init)
to have complete type. */
if (decl
&& DECL_DECOMPOSITION_P (decl)
&& !DECL_DECOMP_BASE (decl)
&& DECL_DECOMP_IS_BASE (decl)
&& !COMPLETE_TYPE_P (type))
{
error_at (DECL_SOURCE_LOCATION (decl),
@ -9438,6 +9438,12 @@ cp_finish_decomp (tree decl, cp_decomp *decomp)
nelts = array_type_nelts_top (type);
if (nelts == error_mark_node)
goto error_out;
if (DECL_DECOMP_BASE (decl))
{
error_at (loc, "array initializer for structured binding "
"declaration in condition");
goto error_out;
}
if (!tree_fits_uhwi_p (nelts))
{
error_at (loc, "cannot decompose variable length array %qT", type);
@ -9537,6 +9543,30 @@ cp_finish_decomp (tree decl, cp_decomp *decomp)
eltscnt = tree_to_uhwi (tsize);
if (count != eltscnt)
goto cnt_mismatch;
if (!processing_template_decl && DECL_DECOMP_BASE (decl))
{
/* For structured bindings used in conditions we need to evaluate
the conversion of decl (aka e in the standard) to bool or
integral/enumeral type (the latter for switch conditions)
before the get methods. */
tree cond = convert_from_reference (decl);
if (integer_onep (DECL_DECOMP_BASE (decl)))
/* switch condition. */
cond = build_expr_type_conversion (WANT_INT | WANT_ENUM,
cond, true);
else
/* if/while/for condition. */
cond = contextual_conv_bool (cond, tf_warning_or_error);
if (cond && !error_operand_p (cond))
{
/* Wrap that value into a TARGET_EXPR, emit it right
away and save for later uses in the cp_parse_condition
or its instantiation. */
cond = get_target_expr (cond);
add_stmt (cond);
DECL_DECOMP_BASE (decl) = cond;
}
}
int save_read = DECL_READ_P (decl);
for (unsigned i = 0; i < count; ++i)
{

2
gcc/cp/decl2.cc
View file

@ -5893,7 +5893,7 @@ mark_used (tree decl, tsubst_flags_t complain /* = tf_warning_or_error */)
TREE_USED (decl) = true;
/* And for structured bindings also the underlying decl. */
if (DECL_DECOMPOSITION_P (decl) && DECL_DECOMP_BASE (decl))
if (DECL_DECOMPOSITION_P (decl) && !DECL_DECOMP_IS_BASE (decl))
TREE_USED (DECL_DECOMP_BASE (decl)) = true;
if (TREE_CODE (decl) == TEMPLATE_DECL)

2
gcc/cp/module.cc
View file

@ -10142,7 +10142,7 @@ trees_in::tree_node (bool is_use)
TREE_USED (res) = true;
/* And for structured bindings also the underlying decl. */
if (DECL_DECOMPOSITION_P (res) && DECL_DECOMP_BASE (res))
if (DECL_DECOMPOSITION_P (res) && !DECL_DECOMP_IS_BASE (res))
TREE_USED (DECL_DECOMP_BASE (res)) = true;
if (DECL_CLONED_FUNCTION_P (res))

46
gcc/cp/parser.cc
View file

@ -2449,7 +2449,7 @@ static void cp_parser_statement_seq_opt
static tree cp_parser_selection_statement
(cp_parser *, bool *, vec<tree> *);
static tree cp_parser_condition
(cp_parser *);
(cp_parser *, enum rid);
static tree cp_parser_iteration_statement
(cp_parser *, bool *, bool, tree, bool);
static bool cp_parser_init_statement
@ -2562,7 +2562,7 @@ static void cp_parser_static_assert
static tree cp_parser_decltype
(cp_parser *);
static tree cp_parser_decomposition_declaration
(cp_parser *, cp_decl_specifier_seq *, tree *, location_t *);
(cp_parser *, cp_decl_specifier_seq *, tree *, location_t *, enum rid);
/* Declarators [gram.dcl.decl] */
@ -13690,7 +13690,7 @@ cp_parser_selection_statement (cp_parser* parser, bool *if_p,
}
/* Parse the condition. */
condition = cp_parser_condition (parser);
condition = cp_parser_condition (parser, keyword);
/* Look for the `)'. */
if (!parens.require_close (parser))
cp_parser_skip_to_closing_parenthesis (parser, true, false,
@ -13909,6 +13909,7 @@ cp_parser_check_condition_declarator (cp_parser* parser,
expression
type-specifier-seq declarator = initializer-clause
type-specifier-seq declarator braced-init-list
structured-binding-declaration initializer (C++26)
GNU Extension:
@ -13919,7 +13920,7 @@ cp_parser_check_condition_declarator (cp_parser* parser,
Returns the expression that should be tested. */
static tree
cp_parser_condition (cp_parser* parser)
cp_parser_condition (cp_parser* parser, enum rid keyword)
{
cp_decl_specifier_seq type_specifiers;
const char *saved_message;
@ -13956,6 +13957,26 @@ cp_parser_condition (cp_parser* parser)
tree initializer = NULL_TREE;
location_t loc = cp_lexer_peek_token (parser->lexer)->location;
/* Look for C++26 structured binding declaration. */
for (size_t n = 1; ; n++)
if (cp_lexer_nth_token_is (parser->lexer, n, CPP_AND)
|| cp_lexer_nth_token_is (parser->lexer, n, CPP_AND_AND))
continue;
else if (cp_lexer_nth_token_is (parser->lexer, n, CPP_OPEN_SQUARE)
&& !cp_lexer_nth_token_is (parser->lexer, n + 1,
CPP_OPEN_SQUARE)
&& type_specifiers.any_specifiers_p
&& cp_parser_parse_definitely (parser))
{
location_t init_loc;
tree decl
= cp_parser_decomposition_declaration (parser, &type_specifiers,
NULL, &init_loc, keyword);
return decl;
}
else
break;
/* Parse the declarator. */
declarator = cp_parser_declarator (parser, CP_PARSER_DECLARATOR_NAMED,
CP_PARSER_FLAGS_NONE,
@ -14095,7 +14116,7 @@ cp_parser_c_for (cp_parser *parser, tree scope, tree init, bool ivdep,
/* If there's a condition, process it. */
if (cp_lexer_next_token_is_not (parser->lexer, CPP_SEMICOLON))
condition = cp_parser_condition (parser);
condition = cp_parser_condition (parser, RID_FOR);
else if (ivdep)
{
cp_parser_error (parser, "missing loop condition in loop with "
@ -14660,7 +14681,7 @@ cp_parser_iteration_statement (cp_parser* parser, bool *if_p, bool ivdep,
matching_parens parens;
parens.require_open (parser);
/* Parse the condition. */
condition = cp_parser_condition (parser);
condition = cp_parser_condition (parser, RID_WHILE);
finish_while_stmt_cond (condition, statement, ivdep, unroll, novector);
/* Look for the `)'. */
parens.require_close (parser);
@ -15966,7 +15987,7 @@ cp_parser_simple_declaration (cp_parser* parser,
tree decl
= cp_parser_decomposition_declaration (parser, &decl_specifiers,
maybe_range_for_decl,
&init_loc);
&init_loc, RID_MAX);
/* The next token should be either a `,' or a `;'. */
cp_token *token = cp_lexer_peek_token (parser->lexer);
@ -16210,7 +16231,7 @@ static tree
cp_parser_decomposition_declaration (cp_parser *parser,
cp_decl_specifier_seq *decl_specifiers,
tree *maybe_range_for_decl,
location_t *init_loc)
location_t *init_loc, enum rid keyword)
{
cp_ref_qualifier ref_qual = cp_parser_ref_qualifier_opt (parser);
location_t loc = cp_lexer_peek_token (parser->lexer)->location;
@ -16269,7 +16290,11 @@ cp_parser_decomposition_declaration (cp_parser *parser,
}
}
if (cxx_dialect < cxx17)
if (keyword != RID_MAX && cxx_dialect < cxx26)
pedwarn (loc, OPT_Wc__26_extensions,
"structured bindings in conditions only available with "
"%<-std=c++2c%> or %<-std=gnu++2c%>");
else if (cxx_dialect < cxx17)
pedwarn (loc, OPT_Wc__17_extensions,
"structured bindings only available with "
"%<-std=c++17%> or %<-std=gnu++17%>");
@ -16357,6 +16382,9 @@ cp_parser_decomposition_declaration (cp_parser *parser,
cp_finish_decl (decl, initializer, non_constant_p, NULL_TREE,
(is_direct_init ? LOOKUP_NORMAL : LOOKUP_IMPLICIT),
&decomp);
if (keyword != RID_MAX)
DECL_DECOMP_BASE (decl)
= keyword == RID_SWITCH ? integer_one_node : integer_zero_node;
cp_finish_decomp (decl, &decomp);
}
}

17
gcc/cp/semantics.cc
View file

@ -966,6 +966,15 @@ maybe_convert_cond (tree cond)
if (type_dependent_expression_p (cond))
return cond;
/* For structured binding used in condition, the conversion needs to be
evaluated before the individual variables are initialized in the
std::tuple_{size,elemenet} case. cp_finish_decomp saved the conversion
result in a TARGET_EXPR, pick it up from there. */
if (DECL_DECOMPOSITION_P (cond)
&& DECL_DECOMP_IS_BASE (cond)
&& TREE_CODE (DECL_DECOMP_BASE (cond)) == TARGET_EXPR)
cond = TARGET_EXPR_SLOT (DECL_DECOMP_BASE (cond));
if (warn_sequence_point && !processing_template_decl)
verify_sequence_points (cond);
@ -1699,6 +1708,14 @@ finish_switch_cond (tree cond, tree switch_stmt)
{
/* Convert the condition to an integer or enumeration type. */
tree orig_cond = cond;
/* For structured binding used in condition, the conversion needs to be
evaluated before the individual variables are initialized in the
std::tuple_{size,elemenet} case. cp_finish_decomp saved the
conversion result in a TARGET_EXPR, pick it up from there. */
if (DECL_DECOMPOSITION_P (cond)
&& DECL_DECOMP_IS_BASE (cond)
&& TREE_CODE (DECL_DECOMP_BASE (cond)) == TARGET_EXPR)
cond = TARGET_EXPR_SLOT (DECL_DECOMP_BASE (cond));
cond = build_expr_type_conversion (WANT_INT | WANT_ENUM, cond, true);
if (cond == NULL_TREE)
{

2
gcc/cp/typeck.cc
View file

@ -10661,7 +10661,7 @@ maybe_warn_about_returning_address_of_local (tree retval, location_t loc)
|| TREE_PUBLIC (whats_returned)))
{
if (DECL_DECOMPOSITION_P (whats_returned)
&& DECL_DECOMP_BASE (whats_returned)
&& !DECL_DECOMP_IS_BASE (whats_returned)
&& DECL_HAS_VALUE_EXPR_P (whats_returned))
{
/* When returning address of a structured binding, if the structured

24
gcc/testsuite/g++.dg/cpp1z/decomp16.C
View file

@ -7,23 +7,23 @@ void
foo ()
{
auto [ a, b ] = A ();
for (; auto [ a, b ] = A (); ) // { dg-error "expected" }
;
for (; auto [ a, b ] = A (); ) // { dg-error "structured bindings in conditions only available with" "" { target c++23_down } }
; // { dg-error "could not convert '<structured bindings>' from 'A' to 'bool'" "" { target *-*-* } .-1 }
for (; false; auto [ a, b ] = A ()) // { dg-error "expected" }
;
if (auto [ a, b ] = A ()) // { dg-error "expected" }
;
if (auto [ a, b ] = A (); auto [ c, d ] = A ()) // { dg-error "expected" }
;
if (int d = 5; auto [ a, b ] = A ()) // { dg-error "expected" }
;
switch (auto [ a, b ] = B ()) // { dg-error "expected" }
{
if (auto [ a, b ] = A ()) // { dg-error "structured bindings in conditions only available with" "" { target c++23_down } }
; // { dg-error "could not convert '<structured bindings>' from 'A' to 'bool'" "" { target *-*-* } .-1 }
if (auto [ a, b ] = A (); auto [ c, d ] = A ()) // { dg-error "structured bindings in conditions only available with" "" { target c++23_down } }
; // { dg-error "could not convert '<structured bindings>' from 'A' to 'bool'" "" { target *-*-* } .-1 }
if (int d = 5; auto [ a, b ] = A ()) // { dg-error "structured bindings in conditions only available with" "" { target c++23_down } }
; // { dg-error "could not convert '<structured bindings>' from 'A' to 'bool'" "" { target *-*-* } .-1 }
switch (auto [ a, b ] = B ()) // { dg-error "structured bindings in conditions only available with" "" { target c++23_down } }
{ // { dg-error "switch quantity not an integer" "" { target *-*-* } .-1 }
case 2:
break;
}
switch (int d = 5; auto [ a, b ] = B ()) // { dg-error "expected" }
{
switch (int d = 5; auto [ a, b ] = B ()) // { dg-error "structured bindings in conditions only available with" "" { target c++23_down } }
{ // { dg-error "switch quantity not an integer" "" { target *-*-* } .-1 }
case 2:
break;
}

15
gcc/testsuite/g++.dg/cpp26/decomp10.C Normal file
View file

@ -0,0 +1,15 @@
// P0963R3 - Structured binding declaration as a condition
// { dg-do compile { target c++11 } }
// { dg-options "" }
_Complex int c;
int __attribute__((__vector_size__ (4 * sizeof (int)))) v;
void
foo ()
{
if (auto [i,j] = c) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
;
if (auto [i,j,k,l] = v) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
; // { dg-error "could not convert '<structured bindings>' from '\[^\n\r]*' to 'bool'" "" { target *-*-* } .-1 }
}

168
gcc/testsuite/g++.dg/cpp26/decomp3.C Normal file
View file

@ -0,0 +1,168 @@
// P0963R3 - Structured binding declaration as a condition
// { dg-do run { target c++11 } }
// { dg-options "" }
namespace std {
template<typename T> struct tuple_size;
template<int, typename> struct tuple_element;
}
struct S {
int a, b;
explicit operator bool () const noexcept { return a == b; }
};
struct T {
int a, b, c;
static int d;
explicit operator bool () const noexcept { d = 42; return a == b; }
template <int I> int &get () { if (d != 42) __builtin_abort (); return I ? a : b; }
};
int T::d = 0;
template<> struct std::tuple_size<T> { static const int value = 2; };
template<int I> struct std::tuple_element<I,T> { using type = int; };
void
foo (T t)
{
if (auto [ i, j ] = S { 1, 1 }) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
if (i != 1 || j != 1)
__builtin_abort ();
}
else
{
++i;
++j;
__builtin_abort ();
}
T::d = 0;
if (int m = 78; auto & [ i, j ] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{ // { dg-warning "init-statement in selection statements only available with" "" { target c++14_down } .-1 }
if (i != 42 || j != 42 || T::d != 42 || m != 78)
__builtin_abort ();
}
else
{
++i;
++j;
++m;
__builtin_abort ();
}
if (auto m = 15; auto [ i, j ] = S { -1, 1 }) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{ // { dg-warning "init-statement in selection statements only available with" "" { target c++14_down } .-1 }
++i;
++j;
++m;
__builtin_abort ();
}
else
{
if (i != -1 || j != 1 || m != 15)
__builtin_abort ();
}
t.a = -42;
T::d = 0;
if (auto & [ i, j ] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
++i;
++j;
__builtin_abort ();
}
else
{
if (i != 42 || j != -42 || T::d != 42)
__builtin_abort ();
}
}
void
bar (T t)
{
int cnt = 0;
while (auto [ i, j ] = S { 7, 7 }) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
if (i != 7 || j != 7)
__builtin_abort ();
if (++cnt == 5)
break;
}
if (cnt != 5)
__builtin_abort ();
T::d = 0;
while (auto & [ i, j ] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
if (i != 31 || j != 31 || T::d != 42)
__builtin_abort ();
T::d = 0;
if (++cnt == 10)
break;
}
if (cnt != 10)
__builtin_abort ();
while (auto [ i, j ] = S { 7, -7 }) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
++i;
++j;
__builtin_abort ();
}
t.a = -31;
T::d = 0;
while (auto & [ i, j ] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
++i;
++j;
__builtin_abort ();
}
}
void
baz (T t)
{
int cntc = 0;
for (int cnt = 0; auto [ i, j ] = S { 12, 12 }; ++cnt) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
if (i != 12 || j != 12)
__builtin_abort ();
cntc = cnt;
if (cnt == 5)
break;
}
if (cntc != 5)
__builtin_abort ();
T::d = 0;
for (int cnt = 5; auto & [ i, j ] = t; ++cnt) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
if (i != -15 || j != -15 || T::d != 42)
__builtin_abort ();
T::d = 0;
cntc = cnt;
if (cnt == 10)
break;
}
if (cntc != 10)
__builtin_abort ();
for (int cnt = 0; auto [ i, j ] = S { -27, 27 }; ++cnt) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
++i;
++j;
__builtin_abort ();
}
t.a = 15;
T::d = 0;
for (int cnt = 0; auto & [ i, j ] = t; ++cnt) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
++i;
++j;
__builtin_abort ();
}
}
int
main ()
{
foo ({ 42, 42, 0 });
bar ({ 31, 31, 7 });
baz ({ -15, -15, 6 });
}

74
gcc/testsuite/g++.dg/cpp26/decomp4.C Normal file
View file

@ -0,0 +1,74 @@
// P0963R3 - Structured binding declaration as a condition
// { dg-do run { target c++11 } }
// { dg-options "" }
namespace std {
template<typename T> struct tuple_size;
template<int, typename> struct tuple_element;
}
struct S {
int a, b;
operator int () const noexcept { return a * 2; }
};
struct T {
int a, b, c;
static int d;
operator long long () const noexcept { d = 42; return a * 4; }
template <int I> int &get () { if (d != 42) __builtin_abort (); return I ? a : b; }
};
int T::d = 0;
template<> struct std::tuple_size<T> { static const int value = 2; };
template<int I> struct std::tuple_element<I,T> { using type = int; };
void
foo (T t)
{
switch (auto [ i, j ] = S { 53, 62 }) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
case 2 * 53:
if (i != 53 || j != 62)
__builtin_abort ();
break;
default:
__builtin_abort ();
}
T::d = 0;
switch (int m = 78; auto & [ i, j ] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{ // { dg-warning "init-statement in selection statements only available with" "" { target c++14_down } .-1 }
case 4 * 42LL:
if (i != 43 || j != 42 || T::d != 42 || m != 78)
__builtin_abort ();
break;
default:
break;
}
switch (auto m = 15; auto [ i, j ] = S { -1, 1 }) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{ // { dg-warning "init-statement in selection statements only available with" "" { target c++14_down } .-1 }
case 2 * -1:
if (i != -1 || j != 1 || m != 15)
__builtin_abort ();
break;
default:
__builtin_abort ();
}
t.a = -42;
T::d = 0;
switch (auto & [ i, j ] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
case 4LL * -42:
if (i != 43 || j != -42 || T::d != 42)
__builtin_abort ();
break;
default:
__builtin_abort ();
}
}
int
main ()
{
foo ({ 42, 43, 0 });
}

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// P0963R3 - Structured binding declaration as a condition
// { dg-do run { target c++11 } }
// { dg-options "" }
namespace std {
template<typename T> struct tuple_size;
template<int, typename> struct tuple_element;
}
struct S {
int a, b;
explicit operator bool () const noexcept { return a == b; }
};
struct T {
int a, b, c;
static int d;
explicit operator bool () const noexcept { d = 42; return a == b; }
template <int I> int &get () { if (d != 42) __builtin_abort (); return I ? a : b; }
};
int T::d = 0;
template<> struct std::tuple_size<T> { static const int value = 2; };
template<int I> struct std::tuple_element<I,T> { using type = int; };
template <int N>
void
foo (T t)
{
if (auto [ i, j ] = S { 1, 1 }) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
if (i != 1 || j != 1)
__builtin_abort ();
}
else
{
++i;
++j;
__builtin_abort ();
}
T::d = 0;
if (int m = 78; auto & [ i, j ] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{ // { dg-warning "init-statement in selection statements only available with" "" { target c++14_down } .-1 }
if (i != 42 || j != 42 || T::d != 42 || m != 78)
__builtin_abort ();
}
else
{
++i;
++j;
++m;
__builtin_abort ();
}
if (auto m = 15; auto [ i, j ] = S { -1, 1 }) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{ // { dg-warning "init-statement in selection statements only available with" "" { target c++14_down } .-1 }
++i;
++j;
++m;
__builtin_abort ();
}
else
{
if (i != -1 || j != 1 || m != 15)
__builtin_abort ();
}
t.a = -42;
T::d = 0;
if (auto & [ i, j ] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
++i;
++j;
__builtin_abort ();
}
else
{
if (i != 42 || j != -42 || T::d != 42)
__builtin_abort ();
}
}
template <int N>
void
bar (T t)
{
int cnt = 0;
while (auto [ i, j ] = S { 7, 7 }) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
if (i != 7 || j != 7)
__builtin_abort ();
if (++cnt == 5)
break;
}
if (cnt != 5)
__builtin_abort ();
T::d = 0;
while (auto & [ i, j ] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
if (i != 31 || j != 31 || T::d != 42)
__builtin_abort ();
T::d = 0;
if (++cnt == 10)
break;
}
if (cnt != 10)
__builtin_abort ();
while (auto [ i, j ] = S { 7, -7 }) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
++i;
++j;
__builtin_abort ();
}
t.a = -31;
T::d = 0;
while (auto & [ i, j ] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
++i;
++j;
__builtin_abort ();
}
}
template <int N>
void
baz (T t)
{
int cntc = 0;
for (int cnt = 0; auto [ i, j ] = S { 12, 12 }; ++cnt) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
if (i != 12 || j != 12)
__builtin_abort ();
cntc = cnt;
if (cnt == 5)
break;
}
if (cntc != 5)
__builtin_abort ();
T::d = 0;
for (int cnt = 5; auto & [ i, j ] = t; ++cnt) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
if (i != -15 || j != -15 || T::d != 42)
__builtin_abort ();
T::d = 0;
cntc = cnt;
if (cnt == 10)
break;
}
if (cntc != 10)
__builtin_abort ();
for (int cnt = 0; auto [ i, j ] = S { -27, 27 }; ++cnt) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
++i;
++j;
__builtin_abort ();
}
t.a = 15;
T::d = 0;
for (int cnt = 0; auto & [ i, j ] = t; ++cnt) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
++i;
++j;
__builtin_abort ();
}
}
int
main ()
{
foo<0> ({ 42, 42, 0 });
bar<0> ({ 31, 31, 7 });
baz<0> ({ -15, -15, 6 });
}

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// P0963R3 - Structured binding declaration as a condition
// { dg-do run { target c++11 } }
// { dg-options "" }
namespace std {
template<typename T> struct tuple_size;
template<int, typename> struct tuple_element;
}
struct S {
int a, b;
operator int () const noexcept { return a * 2; }
};
struct T {
int a, b, c;
static int d;
operator long long () const noexcept { d = 42; return a * 4; }
template <int I> int &get () { if (d != 42) __builtin_abort (); return I ? a : b; }
};
int T::d = 0;
template<> struct std::tuple_size<T> { static const int value = 2; };
template<int I> struct std::tuple_element<I,T> { using type = int; };
template <int N>
void
foo (T t)
{
switch (auto [ i, j ] = S { 53, 62 }) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
case 2 * 53:
if (i != 53 || j != 62)
__builtin_abort ();
break;
default:
__builtin_abort ();
}
T::d = 0;
switch (int m = 78; auto & [ i, j ] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{ // { dg-warning "init-statement in selection statements only available with" "" { target c++14_down } .-1 }
case 4 * 42LL:
if (i != 43 || j != 42 || T::d != 42 || m != 78)
__builtin_abort ();
break;
default:
break;
}
switch (auto m = 15; auto [ i, j ] = S { -1, 1 }) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{ // { dg-warning "init-statement in selection statements only available with" "" { target c++14_down } .-1 }
case 2 * -1:
if (i != -1 || j != 1 || m != 15)
__builtin_abort ();
break;
default:
__builtin_abort ();
}
t.a = -42;
T::d = 0;
switch (auto & [ i, j ] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
case 4LL * -42:
if (i != 43 || j != -42 || T::d != 42)
__builtin_abort ();
break;
default:
__builtin_abort ();
}
}
int
main ()
{
foo<0> ({ 42, 43, 0 });
}

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// P0963R3 - Structured binding declaration as a condition
// { dg-do run { target c++11 } }
// { dg-options "" }
namespace std {
template<typename T> struct tuple_size;
template<int, typename> struct tuple_element;
}
struct S {
int a, b;
explicit operator bool () const noexcept { return a == b; }
};
struct T {
int a, b, c;
static int d;
explicit operator bool () const noexcept { d = 42; return a == b; }
template <int I> int &get () { if (d != 42) __builtin_abort (); return I ? a : b; }
};
int T::d = 0;
template<> struct std::tuple_size<T> { static const int value = 2; };
template<int I> struct std::tuple_element<I,T> { using type = int; };
template <typename S, typename T>
void
foo (T t)
{
if (auto [ i, j ] = S { 1, 1 }) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
if (i != 1 || j != 1)
__builtin_abort ();
}
else
{
++i;
++j;
__builtin_abort ();
}
T::d = 0;
if (int m = 78; auto & [ i, j ] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{ // { dg-warning "init-statement in selection statements only available with" "" { target c++14_down } .-1 }
if (i != 42 || j != 42 || T::d != 42 || m != 78)
__builtin_abort ();
}
else
{
++i;
++j;
++m;
__builtin_abort ();
}
if (auto m = 15; auto [ i, j ] = S { -1, 1 }) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{ // { dg-warning "init-statement in selection statements only available with" "" { target c++14_down } .-1 }
++i;
++j;
++m;
__builtin_abort ();
}
else
{
if (i != -1 || j != 1 || m != 15)
__builtin_abort ();
}
t.a = -42;
T::d = 0;
if (auto & [ i, j ] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
++i;
++j;
__builtin_abort ();
}
else
{
if (i != 42 || j != -42 || T::d != 42)
__builtin_abort ();
}
}
template <typename S, typename T>
void
bar (T t)
{
int cnt = 0;
while (auto [ i, j ] = S { 7, 7 }) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
if (i != 7 || j != 7)
__builtin_abort ();
if (++cnt == 5)
break;
}
if (cnt != 5)
__builtin_abort ();
T::d = 0;
while (auto & [ i, j ] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
if (i != 31 || j != 31 || T::d != 42)
__builtin_abort ();
T::d = 0;
if (++cnt == 10)
break;
}
if (cnt != 10)
__builtin_abort ();
while (auto [ i, j ] = S { 7, -7 }) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
++i;
++j;
__builtin_abort ();
}
t.a = -31;
T::d = 0;
while (auto & [ i, j ] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
++i;
++j;
__builtin_abort ();
}
}
template <typename S, typename T>
void
baz (T t)
{
int cntc = 0;
for (int cnt = 0; auto [ i, j ] = S { 12, 12 }; ++cnt) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
if (i != 12 || j != 12)
__builtin_abort ();
cntc = cnt;
if (cnt == 5)
break;
}
if (cntc != 5)
__builtin_abort ();
T::d = 0;
for (int cnt = 5; auto & [ i, j ] = t; ++cnt) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
if (i != -15 || j != -15 || T::d != 42)
__builtin_abort ();
T::d = 0;
cntc = cnt;
if (cnt == 10)
break;
}
if (cntc != 10)
__builtin_abort ();
for (int cnt = 0; auto [ i, j ] = S { -27, 27 }; ++cnt) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
++i;
++j;
__builtin_abort ();
}
t.a = 15;
T::d = 0;
for (int cnt = 0; auto & [ i, j ] = t; ++cnt) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
++i;
++j;
__builtin_abort ();
}
}
int
main ()
{
foo<S, T> ({ 42, 42, 0 });
bar<S, T> ({ 31, 31, 7 });
baz<S, T> ({ -15, -15, 6 });
}

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// P0963R3 - Structured binding declaration as a condition
// { dg-do run { target c++11 } }
// { dg-options "" }
namespace std {
template<typename T> struct tuple_size;
template<int, typename> struct tuple_element;
}
struct S {
int a, b;
operator int () const noexcept { return a * 2; }
};
struct T {
int a, b, c;
static int d;
operator long long () const noexcept { d = 42; return a * 4; }
template <int I> int &get () { if (d != 42) __builtin_abort (); return I ? a : b; }
};
int T::d = 0;
template<> struct std::tuple_size<T> { static const int value = 2; };
template<int I> struct std::tuple_element<I,T> { using type = int; };
template <typename S, typename T>
void
foo (T t)
{
switch (auto [ i, j ] = S { 53, 62 }) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
case 2 * 53:
if (i != 53 || j != 62)
__builtin_abort ();
break;
default:
__builtin_abort ();
}
T::d = 0;
switch (int m = 78; auto & [ i, j ] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{ // { dg-warning "init-statement in selection statements only available with" "" { target c++14_down } .-1 }
case 4 * 42LL:
if (i != 43 || j != 42 || T::d != 42 || m != 78)
__builtin_abort ();
break;
default:
break;
}
switch (auto m = 15; auto [ i, j ] = S { -1, 1 }) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{ // { dg-warning "init-statement in selection statements only available with" "" { target c++14_down } .-1 }
case 2 * -1:
if (i != -1 || j != 1 || m != 15)
__builtin_abort ();
break;
default:
__builtin_abort ();
}
t.a = -42;
T::d = 0;
switch (auto & [ i, j ] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
case 4LL * -42:
if (i != 43 || j != -42 || T::d != 42)
__builtin_abort ();
break;
default:
__builtin_abort ();
}
}
int
main ()
{
foo<S, T> ({ 42, 43, 0 });
}

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// P0963R3 - Structured binding declaration as a condition
// { dg-do compile { target c++11 } }
// { dg-options "" }
int a[4];
struct S { int i, j; };
struct T { int i, j, k; explicit operator bool () const noexcept; } t;
enum E { E0, E1 };
struct U { int i, j, k, l; operator E () const noexcept; } u;
int w;
union X { int i; long j; } x;
void
foo (const S &&s)
{
if (auto [ i, j, k, l ] = a) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
; // { dg-error "array initializer for structured binding declaration in condition" "" { target *-*-* } .-1 }
if (auto & [a, b, c] = "ht") // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
; // { dg-error "array initializer for structured binding declaration in condition" "" { target *-*-* } .-1 }
if (auto const & [i, j] = s) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
; // { dg-error "could not convert '<structured bindings>' from 'const S' to 'bool'" "" { target *-*-* } .-1 }
if (auto const & [i, j, k] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
w = i + j + k;
else
w = i - j * k;
if (auto [i, j, k, l] = u) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
;
if (auto [i] = x) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
; // { dg-error "cannot decompose union type 'X'" "" { target *-*-* } .-1 }
// { dg-error "could not convert '<structured bindings>' from 'X' to 'bool'" "" { target *-*-* } .-2 }
if (auto [i, j, k] = s) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
; // { dg-error "3 names provided for structured binding" "" { target *-*-* } .-1 }
// { dg-error "could not convert '<structured bindings>' from 'S' to 'bool'" "" { target *-*-* } .-2 }
if (auto [i] = s) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
; // { dg-error "only 1 name provided for structured binding" "" { target *-*-* } .-1 }
// { dg-error "could not convert '<structured bindings>' from 'S' to 'bool'" "" { target *-*-* } .-2 }
switch (auto [a, b, c] = "ht") // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{ // { dg-error "array initializer for structured binding declaration in condition" "" { target *-*-* } .-1 }
default: // { dg-error "switch quantity not an integer" "" { target *-*-* } .-2 }
break;
}
switch (auto const & [i, j] = s) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{ // { dg-error "switch quantity not an integer" "" { target *-*-* } .-1 }
case 1:
default:
break;
}
switch (auto const & [i, j, k] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{ // { dg-error "switch quantity not an integer" "" { target *-*-* } .-1 }
case 1:
default:
break;
}
switch (auto [i, j, k, l] = u) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
{
case E0:
++i; ++j;
break;
default:
++k; ++l;
break;
}
if (static auto [i, j, k] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
; // { dg-error "'static' invalid in condition" "" { target *-*-* } .-1 }
// { dg-warning "structured binding declaration can be 'static' only in" "" { target c++17_down } .-2 }
if (constexpr auto [i, j, k] = t) // { dg-warning "structured bindings in conditions only available with" "" { target c++23_down } }
; // { dg-error "structured binding declaration cannot be 'constexpr'" "" { target *-*-* } .-1 }
}