Re: Default typed argument for a templated argument

"Alf P. Steinbach" <>
Thu, 25 Jun 2009 20:24:46 CST
* Olivier:

Anyway, my real question has to do with the fact that MSVC and GCC are
very happy to compile the 'func' definition despite the fact that you
can't use it relying on the default argument. Why is that ?

Only the compiler developers could answer that, it's a Quality Of

Consider a perhaps more subtle case, where the presence of a default
argument in
one member routine makes another member routine effectively inaccessible:

     struct Foo
         Foo() {} // No way to use this constructor!
         Foo( int = 0 ) {}

     int main()
         Foo( 42 ); // OK.
         Foo(); // Ouch! Ambiguous!

It's very difficult to draw the line about what to warn about, because
slip-up can easily be someone else's intended effect. Consider e.g. warning
about unreachable code, when the intent is a compile time configuration of
code should be present. But I agree that it's even more difficult to imagine
valid usage of a default that can never be invoked, or a member routine
definition that can never be invoked, so, perhaps report this to the

Cheers & hth.,

- Alf

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