| Summary: | Specialized template base class name not accepted | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Ian Lance Taylor <ian> |
| Component: | c++ | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | RESOLVED DUPLICATE | ||
| Severity: | normal | CC: | 3.14159, bangerth, bangerth, fang, gcc-bugs, giovannibajo, ian, jens.maurer, reichelt, s__nakayama, witt |
| Priority: | P3 | Keywords: | rejects-valid |
| Version: | 4.4.0 | ||
| Target Milestone: | --- | ||
| Host: | Target: | ||
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | ||
I don't read from the sentence that this applies to base class names, it says "the name of the template" only. EDG rejects it with
t.C(5): error: argument list for class template "base" is missing
typedef base b;
^
but accepts it if you use derived instead of base (like gcc does).
Here is further argument from a programmer here. Any language lawyers want to comment?
14.6.1 Locally declared names [temp.local]
1. Like normal (non-template) classes, class templates have an injected-class-name (clause 9). The injected-class-name can be used with or without a template-argument-list. When it is used without a template-argument-list, it is equivalent to the injected-class-name followed by the template-parameters of the class template enclosed in <>. When it is used with a template-argument-list, it refers to the specified class template specialization, which could be the current specialization or another specialization.
It makes this code valid:
template <class T>
struct base {
typedef base b;
};
And now according to this:
9 Classes [class]
2 A class-name is inserted into the scope in which it is declared immediately after the class-name is seen. The class-name is also inserted into the scope of the class itself; this is known as the injected-class-name. For purposes of access checking, the injected-class-name is treated as if it were a public member name. A class-specifier is commonly referred to as a class definition. A class is considered defined after the closing brace of its class-specifier has been seen even though its member functions are in general not yet defined.
injected-class-name is public, therefore it is accessible in derived class. It makes the example valid.
|
C++98 [temp.local] says "Within the scope of a class template specialization or partial specialization, when the name of the template is neither qualified nor followed by <, it is equivalent to the name of the template followed by the template-arguments enclosed in <>." That does not work when a template specialization is used as a base class. In that case g++ does not accept the unqualified base class name as a type. This test case: template <class T> struct base {}; struct derived : base<int> { typedef base b; base* p; }; gives these errors: foo.cc:5: error: invalid use of template-name ‘base’ without an argument list foo.cc:6: error: ISO C++ forbids declaration of ‘base’ with no type foo.cc:6: error: expected ‘;’ before ‘*’ token I believe this is an incorrect rejection of valid C++ code. At least, I can't find anything in the C++ standard which says that this code is invalid.