Re: Why koenig lookup?
On Aug 10, 6:45 pm, "Alf P. Steinbach" <al...@start.no> wrote:
* James Kanze:
And of course, in a template, you don't really even have the
choice.
?
In a template, sin will be a dependent name, and will not be
looked up in the global namespace, only in the namespace where
BigDecimal was defined.
If that was true then it would just reinforce the point that
ADL for named routines has turned out to be too problematic,
too many limiting corner cases.
I don't think the problem here is ADL. The problem is two phase
lookup in general.
However,
<code>
#include <iostream>
namespace james
{
struct BigInt {};
}
double sin( james::BigInt ) { return 0; }
template< typename T >
void foo()
{
sin( james::BigInt() );
}
is good standard C++.
But doesn't use sin in a dependent context in a dependent
context in the template. I was thinking of the classical case,
where the operator<< for std::vector<int> defined in global
namespace doesn't get found when it is used in
std::ostream_iterator. Curiously, I can't reproduce the
symptomes in a simple example, but I've definitely had the
problem myself, and people post it here from time to time.
I did say dependent, didn't I, in my first posting. Now, either
two phase lookup is too complicated for even a guru like
yourself to catch onto the subtilities, or you're being
intentionally obtuse. (And regretfully, there's nothing ironic
about that. IMHO, two phase lookup does have enough subtilities
that even an expert can easily overlook them.)
So what you literally write, is incorrect, and argument void.
But still there is a good chance that you had some specific
scenario in mind, that I don't at present grok. And I'm
interested in that, on its own, so please, elaborate. :-)
See above. And the fact that even someone with your level
didn't catch on immediately just confirms my feeling that two
phase lookup, at least in its present form, was a mistake,
because it's just too complicated.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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