Is it possible to NATVIS a recursive tuple (variadic template)? - natvis

Question

I implemented the tuple from here: https://voidnish.wordpress.com/2013/07/13/tuple-implementation-via-variadic-templates/
Is it possible to visualize it with NATVIS? I got as far as
<Type Name="tuple">
<DisplayString>()</DisplayString>
</Type>
<Type Name="tuple<*>">
<DisplayString>({_Myfirst})</DisplayString>
</Type>
How can I get the _Myfirst value for more than one type, to get
<Type Name="tuple<*,*>">
<DisplayString>({_Myfirst}, {???})</DisplayString>
</Type>
<Type Name="tuple<*,*,*>">
<DisplayString>({_Myfirst}, {???}, {???})</DisplayString>
</Type>
etc?

Answer 1

You'll have to modify the type a little to get this to work. What's required is a base_type typedef.
i.e.
// tuple
template<class... _Types> class tuple;
// empty tuple
template<> class tuple<> {};
// recursive tuple definition
template<class _This,
class... _Rest>
class tuple<_This, _Rest...>
: private tuple<_Rest...>
{
public:
typedef tuple<_Rest...> base_type; // ***** Added this line
_This _Myfirst;
};
Now we can recursively evaluate the base types with the natvis declarations:
<!-- Handle empty tuples -->
<Type Name="tuple<>">
<DisplayString>()</DisplayString>
<Expand/>
</Type>
<!-- Handle a single parameter (this is also our terminator for recursion) -->
<Type Name="tuple<*>">
<DisplayString IncludeView="noparens">{_Myfirst}</DisplayString>
<DisplayString ExcludeView="noparens">({_Myfirst})</DisplayString>
<Expand>
<Item Name="Value">_Myfirst</Item>
</Expand>
</Type>
<!-- Handle 2 or more items -->
<Type Name="tuple<*,*>">
<!-- show the first item and then recurse by casting this to 'base_type' -->
<DisplayString IncludeView="noparens">{_Myfirst}, {*(base_type *)this,view(noparens)}</DisplayString>
<!-- Wrap our display string that doesn't a have any parentheses, this will be only done for the top level tuple -->
<DisplayString ExcludeView="noparens">({*this,view(noparens)})</DisplayString>
<Expand>
<!-- Show the top level item -->
<Item Name="Value">_Myfirst</Item>
<!-- Recursively expand our base types -->
<ExpandedItem>*(base_type *)this</ExpandedItem>
</Expand>
</Type>
And this is the result: