__ ____ ____ ____ ____
_|__ _|__ _|__ _|__ _|
|____|_C++|____|____|_
__|____|WALL|____|____|
|____|____|____|____|specify template parameters for ctor
Author
You can't use explicit template instantiation with constructors. One option is to use a type-type parameter. ex:
template <typename T>struct TypeType { typedef T type;};
Author
Thanks SiCrane
For this particular instance it makes more sense to use a static method in place of this "special" ctor
But that typedef trick is something I wouldn't of thought of :] cheers
so many oddities... :/ why does c++ allow you to declare them if you can't call them?
For this particular instance it makes more sense to use a static method in place of this "special" ctor
But that typedef trick is something I wouldn't of thought of :] cheers
so many oddities... :/ why does c++ allow you to declare them if you can't call them?
Quote:Original post by SiCrane
You can't use explicit template instantiation with constructors.
*cough* explicit template argument passing *cough*
This is the problem, right?
If I've got you this far... this begs the question, why *isn't* the class templated on that type? What can you do that's meaningful with the templated ctor if there's no templated storage within the class (which would require a class template) and there are no ctor parameters dependant on the template? O_O
class foo { template <typename T> foo() { delete new T(); // stupid example }};int main() {foo<int> f; // oops, tries to make a foo<int>, rather than telling the foo ctor to// allocate and then deallocate an int.}// bar.cpp: In function `int main()':// bar.cpp:9: error: `foo' is not a template// bar.cpp:9: error: no matching function for call to `foo::foo()'// bar.cpp:1: note: candidates are: foo::foo(const foo&)If I've got you this far... this begs the question, why *isn't* the class templated on that type? What can you do that's meaningful with the templated ctor if there's no templated storage within the class (which would require a class template) and there are no ctor parameters dependant on the template? O_O
Quote:Original post by Zahlman
What can you do that's meaningful with the templated ctor if there's no templated storage within the class (which would require a class template) and there are no ctor parameters dependant on the template? O_O
Lots of things, for instance the template parameter could be a child type of a type whose associated pointer type is a datamember. The constructor can initialize the pointer datamember to a newly allocated instance of the child type. Also, the template parameter can be used as a form of "named constructor." I.E. Perhaps sometimes you wish to construct an object in a certain way which takes no runtime datamembers and other times you wish to initialize it in another fasion. Neither may logically have to take function arguments -- what you really want is two separately named constructors, which isn't possible. Your alternative is to template the constructor, make a non-template function argument which determines which way to initialize the object, or use entirely separate functions to create and return the object (which would either require the object to have a copy constructor or be dynamically allocated).
Author
stored as abstract base class ;]
extra:
hmm, forgot that the template type could only be created once the first type had been allocated - so the static is out
I've switched to using a real ctor & the template method that you suggested SiCrane.. but with one exception:
template <typename Type> struct Template_type {};
no need for a typedef :P
template <typename Type> Structure::Structure(Template_type<Type> type)
thanks all
[Edited by - ProPuke on September 11, 2005 12:25:33 AM]
extra:
hmm, forgot that the template type could only be created once the first type had been allocated - so the static is out
I've switched to using a real ctor & the template method that you suggested SiCrane.. but with one exception:
template <typename Type> struct Template_type {};
no need for a typedef :P
template <typename Type> Structure::Structure(Template_type<Type> type)
thanks all
[Edited by - ProPuke on September 11, 2005 12:25:33 AM]
This topic is closed to new replies.
Advertisement
Popular Topics
Advertisement
