Re: [boost] [heap] typedef T gets prevalence over template parameter

Subject: Re: [boost] [heap] typedef T gets prevalence over template parameter
From: Alex Hagen-Zanker (ahh34_at_[hidden])
Date: 2012-09-07 05:27:55

On 07/09/2012 08:40, Tim Blechmann wrote:
>> The d_ary_heap does not compile (in VS2010) when the Comparison class
>> contains a typedef T. The typedef takes prevalence over the template
>> parameter T when the heap is derived from the Comparison class.
>>
>> I.e. the following pattern occurs:
>>
>> template<class T, class Cmp> struct heap_base : Cmp
>> {
>>       typedef T value_type; // value_type = Cmp::T
>> }
>>
>> I don't know if this is a bug, a user issue, or a compiler issue. But it
>> caused me a lot of headache when I was trying to apply Jeremiah's
>> indirect_cmp with Boost.Heap.
> hm ... this code works with gcc and with clang ... afaict, msvc does not
> resolve T correctly.
>
> not sure what is the best way to work around this, as every identifier
> that we can use instead of T could also clash with a declaration in Cmp :/
>
> tim
You could have a workaround like this:

template<typename T, typename U, typename Parent>
struct B_args
{
   typedef T T;
   typedef U U;
   typedef Parent Parent;
};

template<typename T, typename U, typename Parent>
struct B : B_args<T, U, Parent> , Parent
{
   typedef typename B_args::T value_type;
};

as a replacement for:

template<typename T, typename U, typename Parent>
struct B : Parent
{
   typedef T value_type;
};