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C++11 [class.ctor]p5 says that

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A defaulted default constructor for a class X is defined as deleted if [...]
    -  X is a union and all of its variant members are of const-qualified type.

A pedantic reading therefore says that

 union X { };

has a deleted default constructor, which is both silly and almost
certainly unintended. Pretend as if this this read

    - X is a union with one or more variant members, and all of its
      variant members are of const-qualified type. 

llvm-svn: 151394
This commit is contained in:
Douglas Gregor 2012-02-24 21:25:53 +00:00
parent 2120e2bd73
commit 232ee49c7b
2 changed files with 10 additions and 6 deletions
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8
clang/lib/Sema/SemaDeclCXX.cpp
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@ -4531,7 +4531,8 @@ bool SpecialMemberDeletionInfo::shouldDeleteForField(FieldDecl *FD) {
} }
// At least one member in each anonymous union must be non-const // At least one member in each anonymous union must be non-const
if (CSM == Sema::CXXDefaultConstructor && AllVariantFieldsAreConst) if (CSM == Sema::CXXDefaultConstructor && AllVariantFieldsAreConst &&
FieldRecord->field_begin() != FieldRecord->field_end())
return true; return true;
// Don't try to initialize the anonymous union // Don't try to initialize the anonymous union
@ -4611,7 +4612,10 @@ bool SpecialMemberDeletionInfo::shouldDeleteForField(FieldDecl *FD) {
/// A defaulted default constructor for a class X is defined as deleted if /// A defaulted default constructor for a class X is defined as deleted if
/// X is a union and all of its variant members are of const-qualified type. /// X is a union and all of its variant members are of const-qualified type.
bool SpecialMemberDeletionInfo::shouldDeleteForAllConstMembers() { bool SpecialMemberDeletionInfo::shouldDeleteForAllConstMembers() {
return CSM == Sema::CXXDefaultConstructor && inUnion() && AllFieldsAreConst; // This is a silly definition, because it gives an empty union a deleted
// default constructor. Don't do that.
return CSM == Sema::CXXDefaultConstructor && inUnion() && AllFieldsAreConst &&
(MD->getParent()->field_begin() != MD->getParent()->field_end());
} }
/// Determine whether a defaulted special member function should be defined as /// Determine whether a defaulted special member function should be defined as

8
clang/test/SemaCXX/cxx0x-deleted-default-ctor.cpp
View File

@ -121,11 +121,11 @@ late_delete::late_delete() = default; // expected-error {{would delete it}}
// See also rdar://problem/8125400. // See also rdar://problem/8125400.
namespace empty { namespace empty {
static union {}; // expected-error {{implicitly-deleted default constructor}} expected-note {{here}} static union {};
static union { union {}; }; // expected-error {{implicitly-deleted default constructor}} expected-note {{here}} static union { union {}; };
static union { struct {}; }; static union { struct {}; };
static union { union { union {}; }; }; // expected-error {{implicitly-deleted default constructor}} expected-note {{here}} static union { union { union {}; }; };
static union { union { struct {}; }; }; static union { union { struct {}; }; };
static union { struct { union {}; }; }; // expected-error {{implicitly-deleted default constructor}} expected-note {{here}} static union { struct { union {}; }; };
static union { struct { struct {}; }; }; static union { struct { struct {}; }; };
} }