Function lookup as metaprogramming
in [C++]
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From: tohava on 2 Feb 2010 21:48 I would like to have several classes which do the following: - HasSymbol<T>::value is true iff T has a symbol called f - HasFunction<T>::value is true iff T has a function called f - HasFunctionWithReturnType<T, S>::value is true iff T has a function called f which returns T - HasFunctionWithThreeParams<T>::value is true iff T is a function accepting 3 params - HasFunctionWithPrototype<T, ???>::value is true iff T has a prototype given somehow through the question marks has this been done before? -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: Jeffrey Schwab on 1 Mar 2010 12:22 On 2010-02-03 03:48:34 -0500, tohava said: > I would like to have several classes which do the following: > - HasSymbol<T>::value is true iff T has a symbol called f > - HasFunction<T>::value is true iff T has a function called f > - HasFunctionWithReturnType<T, S>::value is true iff T has a function > called f which returns T > - HasFunctionWithThreeParams<T>::value is true iff T is a function > accepting 3 params > - HasFunctionWithPrototype<T, ???>::value is true iff T has a > prototype given somehow through the question marks > > has this been done before? Yes, using SFINAE; see Boost enable_if. -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: Mathias Gaunard on 4 Mar 2010 03:06 On Feb 3, 2:48 pm, tohava <toh...(a)gmail.com> wrote: > I would like to have several classes which do the following: > - HasSymbol<T>::value is true iff T has a symbol called f > - HasFunction<T>::value is true iff T has a function called f > - HasFunctionWithReturnType<T, S>::value is true iff T has a function > called f which returns T > - HasFunctionWithThreeParams<T>::value is true iff T is a function > accepting 3 params > - HasFunctionWithPrototype<T, ???>::value is true iff T has a > prototype given somehow through the question marks > > has this been done before? Yes, this can be done using SFINAE, albeit it does require a few tricks and doesn't perfectly work (you can't detect constructors, for example). In C++0x, however, you can use SFINAE to test whether arbitrary expressions are valid, which makes it much better as you can consider conversions etc. -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: Jeffrey Schwab on 4 Mar 2010 21:25 On 3/4/10 3:06 PM, Mathias Gaunard wrote: > On Feb 3, 2:48 pm, tohava<toh...(a)gmail.com> wrote: >> I would like to have several classes which do the following: >> - HasSymbol<T>::value is true iff T has a symbol called f >> - HasFunction<T>::value is true iff T has a function called f ..... >> has this been done before? > Yes, this can be done using SFINAE, albeit it does require a few > tricks and doesn't perfectly work (you can't detect constructors, for > example). > In C++0x, however, you can use SFINAE to test whether arbitrary > expressions are valid, which makes it much better as you can consider > conversions etc. Mathias, I was not aware of the SFINAE improvements. Could you please provide a link, or some relevant code that works in 0x but not in 98? -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: Mathias Gaunard on 5 Mar 2010 02:28 On Mar 5, 2:25 pm, Jeffrey Schwab <j...(a)schwabcenter.com> wrote: > Mathias, I was not aware of the SFINAE improvements. Could you please > provide a link, or some relevant code that works in 0x but not in 98? http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2634.html -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
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