[GCC-XML] Default parameter values in member functions of templated classes.

Roman Yakovenko roman.yakovenko at gmail.com
Tue Feb 26 01:54:18 EST 2008

On Tue, Feb 26, 2008 at 8:27 AM, Bryan Ischo <bji-gccxml at ischo.com> wrote:
> Brad King wrote:
>  > I think what happens is that GCC's expression-to-string conversion is
>  > designed to be used during error message construction.  GCC error
>  > messages look like this:
>  >
>  > error:   initializing argument 1 of 'std::basic_string<_CharT,
>  > _Traits, _Alloc>::basic_string(const _CharT*, const _Alloc&) [with
>  > _CharT = char, _Traits = std::char_traits<char>, _Alloc =
>  > std::allocator<char>]'
>  >
>  > (the code tried to construct std::string(1) which is an error).  Note
>  > that the prototype is given with the template formal parameters
>  > instead of the actual arguments.  Then the rest of the message maps
>  > the parameters to their values.  GCC-XML is using the same
>  > expression-to-string functionality from GCC.  This is not the only
>  > limitation of the expression-to-string conversion that people have
>  > encountered.  In general I think the "default" attribute is useful
>  > mostly for human reference.
>  Can you elaborate on the other limits in the expression-to-string
>  conversion that people have encountered?  It would help me to know about
>  these things instead of discovering them later on myself.
>  As to the utility of correct default attributes - I had wanted to use
>  the text in the default attribute directly in generated C++ code, but it
>  wasn't working for defaults like the problematic one I wrote about.  So
>  I scrapped that, and instead just give the user the text string of the
>  default value to do with what they will.  It's just for completeness of
>  my API (the xrtti "extended runtime typing for C++" system) that I want
>  to be able to provide programmatic representations of the defaults to
>  the API users, not because I have any particular use case in which valid
>  default values would be useful.  Perhaps I should submit a feature
>  request in the gccxml bug database for better expression-to-string
>  handling, especially with regards to default values?

>From my experience only "very simple" default value expressions work.
"Very simple" defined as POD, default constructor of non template class.

For more information I suggest to take a look on issues I have
and solution for some of them:


Roman Yakovenko
C++ Python language binding

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