[cfe-dev] On instantiations of template declarations.

[Abramo Bagnara]

Il 01/06/2010 18:41, Abramo Bagnara ha scritto:
> Il 01/06/2010 17:44, Douglas Gregor ha scritto:
>>
>> On Jun 1, 2010, at 7:38 AM, Enea Zaffanella wrote:
>>> Consider now the following variant, where we have a static data member:
>>>
>>> template <typename T>
>>> struct A { static int a; };
>>>
>>> template <typename T>
>>> int A<T>::a = 0;
>>>
>>> A<int> si;
>>> A<double> sd;
>>>
>>> void bar() {
>>>   sd.a = 13;
>>> }
>>>
>>> Here, we have two implicit instantiations of the template A.
>>> Each of those declares the corresponding static data member.
>>> For one of those (A<double>), we also have an implicit instantiation of 
>>> the *definition* of the static data member A<double>::a.
>>> This implicit definition is reachable starting from the implicit 
>>> declaration using method:
>>>
>>>   VarDecl* VarDecl::getOutOfLineDefinition();
>>>   If this is a static data member, find its out-of-line definition.
>>>
>>> Strangely, the very same implicit definition is also listed in the 
>>> context of the translation unit. This can be seen when dumping the AST, 
>>> just after the definition of function bar():
>>>
>>> ===================
>>> [...]
>>> void bar() (CompoundStmt 0x2151fb0 <var_template.cc:10:12, line:12:1>
>>>   (BinaryOperator 0x216be70 <line:11:3, col:10> 'int' '='
>>>     (MemberExpr 0x216bdf0 <col:3, col:6> 'int' .a 0x216b160
>>>       (DeclRefExpr 0x216bdb0 <col:3> 'A<double>':'struct A<double>' 
>>> Var='sd' 0x216ae10))
>>>     (IntegerLiteral 0x216be30 <col:10> 'int' 13)))
>>>
>>>
>>> static int a = (IntegerLiteral 0x216a8d0 <var_template.cc:5:15> 'int' 0)
>>> ;
>>> ===================
>>>
>>> So, finally, our question is: why such a difference?
>>>
>>> That is, why does the translation unit context contains these 
>>> (implicitly instantiated) definitions of static data members?
>>> It was not containing the (implicitly instantiated) specialization of 
>>> the class template ... or of its methods.
>>
>> Definitely a bug. Implicit instantiations should not show up in the translation unit context.
> 
> The attached patch should fix this, right? Should I commit it?

Ping.