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Ivan Godard
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 Posted: Fri Apr 22, 2005 1:30 pm Post subject: template template function parameters? |
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I have need of a class template one of whose arguments is a function
template - *not* a single instance of a template function, but the
actual function template itself to be called with different argument
types at different points. I expected something like:
template<typename U, template struct Foo {
... X x; Y y;
... if (pred(x) && pred(y))...
};
template<typename T>
bool predAct(T& t) {...}
Foo<int, predAct> f;
but no joy. Some Googling shows class template template parameters, but
no function template template parameters. Do they not exist in the
language, or do I have the syntax wrong? If the former, is there an
idiom that provides the effect?
Thanks
Ivan
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Cyril
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| Posted: Sat Apr 23, 2005 2:29 am Post subject: Re: template template function parameters? |
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Create a object with an () operator in which you've included your
function definition.
Then use this object as a template (no need for "function template"
like you named them)
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Alex Beluga
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| Posted: Sat Apr 23, 2005 9:21 am Post subject: Re: template template function parameters? |
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The idiom which might help you is functor template.
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Ben Hutchings
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| Posted: Sat Apr 23, 2005 9:21 am Post subject: Re: template template function parameters? |
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Ivan Godard wrote:
| Quote: | I have need of a class template one of whose arguments is a function
template - *not* a single instance of a template function, but the
actual function template itself to be called with different argument
types at different points. I expected something like:
template<typename U, template struct Foo {
... X x; Y y;
... if (pred(x) && pred(y))...
};
template<typename T
bool predAct(T& t) {...}
Foo
but no joy. Some Googling shows class template template parameters, but
no function template template parameters. Do they not exist in the
language, or do I have the syntax wrong? If the former, is there an
idiom that provides the effect?
|
They don't exist in the language. You can use a function object class
as a wrapper:
template<typename U, typename Pred> struct Foo {
... X x; Y y; Pred pred;
... if (pred(x) && pred(y))...
};
struct predAct {
template<typename T> bool operator()(T& t) const {...}
};
Foo<int, predAct> f;
--
Ben Hutchings
Having problems with C++ templates? Your questions may be answered by
<http://womble.decadentplace.org.uk/c++/template-faq.html>.
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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