[Bug c++/17011] [3.4/3.5 regression] invalid default parameter diagnosed too late

["mark at codesourcery dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From mark at codesourcery dot com  2004-08-12 22:20 -------
Subject: Re:  [3.4/3.5 regression] invalid default parameter
 diagnosed too late

bangerth at dealii dot org wrote:

>------- Additional Comments From bangerth at dealii dot org  2004-08-12 21:12 -------
>I had to do some research when discussing a bug within IBM's xlC compiler a week ago, 
>and here simply paste a piece from a mail to them that also seems relevant in the 
>present context: 
>----------------------------------- 
>However, here's the catch: let's assume that we may cause an implicit  
>instantiation. Then, 14.7.1/1 says: "The implicit instantiation of a class  
>template specialization causes the instantiation of the declarations, but  
>not of the definitions or default arguments...".  
> 
>Furthermore, 14.7.2 says: "Unless a call is to a [...] member function of  
>an explicitly specialized class template, a default argument for a [...]  
>member function of a class template is implicitly instantiated when the  
>function is called in a context that requires the value of the default  
>argument." 
> 
>Additionally, 14.7.1/11 indicates to me that default arguments are only  
>evaluated at the point where they are actually used. 
>----------------------------------- 
> 
>This all may or may not be imminent here, but it at least points to the right paragraphs 
>that state when exactly a default argument shall be evaluated. 
>  
>
That's a good point.  I forgot about that.  I'm not sure exactly how it 
plays in with the QoI issue in 17011; it might mean that it would be 
invalid for the compiler to issue a diagnostic, or it might nt.  But, 
it's certainly interesting.



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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17011