Re: [Boost-users] [SmartPtr] shared_ptr as a default value in function template

Subject: Re: [Boost-users] [SmartPtr] shared_ptr as a default value in function template
From: Jeff Flinn (Jeffrey.Flinn_at_[hidden])
Date: 2013-05-23 10:49:08

On 5/23/2013 9:57 AM, Pekka Seppänen wrote:
> On 23.5.2013 16:40, Igor R wrote:
>>> It seems to be a MSVC related issue; Unless the templated function
>>> (make_shared in this case) is in the same namespace as the called
>>> templated
>>> function (f in this case) MSVC throws an error.
>>
>>
>> Good finding, thanks!
>>
>> Note however that the following does compile in MSVC:
>>
>> #include <boost/shared_ptr.hpp>
>> #include <boost/make_shared.hpp>
>> void f(int, boost::shared_ptr<int> = boost::make_shared<int>())
>> { }
>> int main()
>> {
>>    f(0);
>> }
>>
>> So, it's still unclear in what cases exactly this bug occurs.
>
> The bug occurs if both the default argument and the function that has
> the default argument are templated. There could be some other cases too,
> but either a) move everything under the same namespace scope, b) drop
> f() template, c) drop default argument template (eg. non-templated
> make_shared wrapper if the make_shared type does not relate to f()'s
> templated type T); Every option sucks, just pick your poison.
>
> So, template < typename T > void foo(T, arg_type arg = ns::templated<
> some_type >()) does not work, but void foo (arg_type arg =
> ns::templated< some_type >()) and template < typename T > void foo(T,
> arg_type arg = ns::not_templated()) work.
>
> Typical MSVC everyday bs...

and the above code continues to faile to compile with MSVC11.

Jeff