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Chris Jefferson
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 Posted: Wed Mar 23, 2005 11:02 pm Post subject: How much is it possible to examine templated functions? |
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Is it possible to somehow "capture" or study templated functions without
a specific instansation, so they can be passed around?
I came across this problem a while ago and couldn't figure out any way
of doing it without wrapping it in a class
ie given:
template<class T>
void foo(T& t);
I can't somehow pass "foo" around without instansating it.
However given:
struct c {
template <class T>
void foo(T& t);
};
I can pass around a c, and use that to get to f.
Now I'm coming at this from the other end. I currently have a templated
function like:
template<class It, class val>
It find(It,It,const val&);
and I want to replace this with:
template<class It, class val>
typename my_enable_if<It,condition>::type find(It,It,const val&);
template<class It, class val>
typename my_enable_if<It,!condition>::type find(It,It,const val&);
(my_enable_if is a template very much like enable_if)
Is there any way at all to detect I've done this? If there is I can hide
this, but if it's impossible to detect then I may as well leave it like
this :)
Thank you,
Chris
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Carl Barron
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| Posted: Thu Mar 24, 2005 11:58 am Post subject: Re: How much is it possible to examine templated functions? |
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In article <d1sf31$g9t$1 (AT) pump1 (DOT) york.ac.uk>, Chris Jefferson
<caj (AT) cs (DOT) york.ac.uk> wrote:
| Quote: |
and I want to replace this with:
template<class It, class val
typename my_enable_if
how about: |
template <class It,class Val>
It find(typename my_enable_if<It,condition>::type begin,It end,const
Val &val);
?
seems like this will only succeed [assuming my_enable_if<It,cond> is
the same as boost::enable_if_c<cond,It>. as this then requires the
first arg to match the condition, and the second arg. If the condition
falis there is no type member, so its not used to find a find template
that matched.
using boost it is
template <class It,class Val>
It find(typename boost::enable_if_c<some_boolean::type
first, It second,Val const &val) { /* ...*/} or forwarded with only a ;
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Gabriel Dos Reis
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| Posted: Fri Mar 25, 2005 1:06 am Post subject: Re: How much is it possible to examine templated functions? |
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Carl Barron <cbarron413 (AT) adelphia (DOT) net> writes:
| Quote: | In article <d1sf31$g9t$1 (AT) pump1 (DOT) york.ac.uk>, Chris Jefferson
[email]caj (AT) cs (DOT) york.ac.uk[/email]> wrote:
and I want to replace this with:
template<class It, class val
typename my_enable_if
how about:
template <class It,class Val
It find(typename my_enable_if
Val &val);
?
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That is not exactly the same thing. With Chris' version, the first
two arguments must be of the same type. With your version, that
requirement is lifted.
--
Gabriel Dos Reis
[email]gdr (AT) integrable-solutions (DOT) net[/email]
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Chris Jefferson
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| Posted: Fri Mar 25, 2005 11:58 am Post subject: Re: How much is it possible to examine templated functions? |
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Carl Barron wrote:
| Quote: | In article <d1sf31$g9t$1 (AT) pump1 (DOT) york.ac.uk>, Chris Jefferson
[email]caj (AT) cs (DOT) york.ac.uk[/email]> wrote:
and I want to replace this with:
template<class It, class val
typename my_enable_if
how about:
template <class It,class Val
It find(typename my_enable_if
Val &val);
?
|
The problem I'm having stems from the fact that I want to know if it's
possible for someone to detect if
template<class It, class val>
It find(It,It,val);
is being implemented by two seperate functions, at most one of which
will be valid for any particular It (by using enable_if). It is true
that I might be able to put the enable_if in different places, but the
important question (to me) is can the existance of two functions be
detected? :)
Chris
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Carl Barron
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| Posted: Sat Mar 26, 2005 5:33 pm Post subject: Re: How much is it possible to examine templated functions? |
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In article <4243E834.3060903 (AT) cs (DOT) york.ac.uk>, Chris Jefferson
<caj (AT) cs (DOT) york.ac.uk> wrote:
| Quote: | The problem I'm having stems from the fact that I want to know if it's
possible for someone to detect if
template
It find(It,It,val);
is being implemented by two seperate functions, at most one of which
will be valid for any particular It (by using enable_if). It is true
that I might be able to put the enable_if in different places, but the
important question (to me) is can the existance of two functions be
detected? :)
Enable_if and the others on the same 'sublibrary' can restrict the |
selection process, to eliminate unwanted matches by SFINAE but they do
not detect that that is more than one candidate if they were not used.
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