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Thant Tessman
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 Posted: Fri Jun 24, 2005 6:40 am Post subject: question on the standard regarding templates, inheritance, a |
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Someone was trying to compile some code of mine with gcc 3.4.3 (which I
don't have) and running into the following problem. Given a
parameterized base class like so:
template <typename T>
struct Base {
inline void blah() {/*whatever*/}
};
Does a derived class have to qualify the use of "blah" with the base
class name? That is, am I supposed to need to do this:
template <typename T>
struct Derived : Base<T> {
inline void blahBlah() {
Base<T>::blah();
}
};
Or am I supposed to be allowed to merely do this:
template <typename T>
struct Derived : Base<T> {
inline void blahBlah() {
blah();
}
};
gcc 3.4.3 wants the name qualified, but none of the compilers I use do.
Luckily the older compilers don't care if I add the scope
qualifications, but I'm really curious if this is merely a case where
3.4.3 is more standards-conforming, or if it's just being quirky.
Thanks for any info,
-thant
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Alf P. Steinbach
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| Posted: Fri Jun 24, 2005 8:46 am Post subject: Re: question on the standard regarding templates, inheritanc |
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* Thant Tessman:
| Quote: |
Someone was trying to compile some code of mine with gcc 3.4.3 (which I
don't have) and running into the following problem. Given a
parameterized base class like so:
template <typename T
struct Base {
inline void blah() {/*whatever*/}
};
Does a derived class have to qualify the use of "blah" with the base
class name?
|
No, but it has to tell the compiler in some way that the function is a
base class member function.
| Quote: | That is, am I supposed to need to do this:
template
struct Derived : Base
inline void blahBlah() {
Base<T>::blah();
}
};
|
You can do
1) Base<T>::blah();
2) this->blah();
3) using Base<T>::blah; inline void blahBlah(){ blah(); }
The first is Good if you really always want the Base<T> version, also in
derived classes, and Bad if that isn't necessarily what you want and blah()
can be virtual.
| Quote: | Or am I supposed to be allowed to merely do this:
template <typename T
struct Derived : Base
inline void blahBlah() {
blah();
}
};
|
No, that shouldn't compile. I think however this was commonly accepted before
standardization of the language. But I'm not sure about that bit of history.
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
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Gene Bushuyev
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| Posted: Fri Jun 24, 2005 11:11 am Post subject: Re: question on the standard regarding templates, inheritanc |
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A short answer: T is a dependent type, Base template will not be looked up,
so you need to use fully qualified name Base<T>::blah() in derived class.
"Thant Tessman" <thant (AT) acm (DOT) org> wrote
| Quote: |
Someone was trying to compile some code of mine with gcc 3.4.3 (which I
don't have) and running into the following problem. Given a
parameterized base class like so:
template <typename T
struct Base {
inline void blah() {/*whatever*/}
};
Does a derived class have to qualify the use of "blah" with the base
class name? That is, am I supposed to need to do this:
template
struct Derived : Base
inline void blahBlah() {
Base<T>::blah();
}
};
|
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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