Re: [Boost-users] [MSM] state transitions and exceptions

Subject: Re: [Boost-users] [MSM] state transitions and exceptions
From: Dave Abrahams (dave_at_[hidden])
Date: 2012-04-05 10:48:13

on Thu Apr 05 2012, Steven Watanabe <watanabesj-AT-gmail.com> wrote:

> AMDG
>
> On 04/04/2012 06:07 PM, Dave Abrahams wrote:
>> 
>> Plus, the way the language is defined, ordering is very important.
>> There's a point of definition and various points of instantiation...
>> particular lookups are done in those locations, and the symbol table has
>> to be right in each case, at least with respect to the symbols used in
>> the template.  I doubt it's easy to unwind those dependencies.
>> 
>
> But...
>
> "If the function name is an unqualified id and the call ...
> would find a better match had the lookup within the associated
> namespaces considered all the function declarations with
> external linkage introduced within those namespaces in
> all translation units, not just considering those declarations
> found in the template declaration and template instantiation
> contexts, then the program has undefined behavior." (14.6.4.2)
>
> "If a template, a member template, or a member of a class
> template is explicitly specialized, then the specialization
> shall be declared before the first use of that specialization
> that would cause an implicit instantiation to take place...
> no diagnostic is required"  (14.7.3)
> (There is a similar clause for partial specialization)
>
> In other words, it seems to me that in most cases where
> delaying the point of instantiation would change the
> behavior it is either undefined behavior or ill-formed,
> no diagnostic required.

But "most cases" is not enough.  If you can show that's true in *all*
cases, there may be a case for parallel template instantiation.

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com