C++ Partial Template Specialization and Natvis

Question

I'm trying to create Visual Studio debug visualizers for a partially specialized type. For example, let's say I have something like this:

template <typename T>
struct Foo
{
    T bar;
};

template <typename T>
struct Foo<T*>
{
    T baz;
};

Without the partial specialization, this would be easy:

<Type Name="Foo&lt;*&gt;"> ... </Type>

With full specialization, it'd also be easy:

<Type Name="Foo&lt;int&gt;"> ... </Type>

But how do I cover the partial specialization? Is this even supported? If not, is there a workaround?

Answer 1

Short answer - No. You can't specify type qualifiers, references, and so on in natvis type name <Type Name="Foo&lt;*&gt;">.

But:

You can use the template's typename parameter as a string and compare with a type. For example, in the node's Condition attribute:

<Type Name="Foo&lt;*&gt;">
  <DisplayString Condition="strcmp(&quot;$T1&quot;,&quot;short&quot;)==0">specialization short</DisplayString>
  <DisplayString Condition="strcmp(&quot;$T1&quot;,&quot;int &amp;&quot;)==0">specialization int &amp;</DisplayString>
  <DisplayString>unspecified specialization</DisplayString>
</Type>

For Foo<short> you will see specialization short and unspecified specialization for other.

Example:

template <typename T, typename U>
struct Foo
{
    T bar;
};

template <typename U>
struct Foo<int &, U>
{
    U baz;
};
int main()
{
    int gg = 0;
    Foo<short, int> a;
    Foo<int, int> b;
    Foo<int &, int> c;

Natvis:

<Type Name="Foo&lt;*,*&gt;" >
  <DisplayString Condition="strcmp(&quot;$T1&quot;,&quot;short&quot;)==0">specialization short</DisplayString>
  <DisplayString>unspecified specialization</DisplayString>
</Type>

<Type Name="Foo&lt;int&amp;,*&gt;">
  <DisplayString>partial specialization int&amp;</DisplayString>
</Type>

Result:

Or you, if you have some unique member in your partially specialized type, can use Priority option.

Example:

template <typename T>
struct Foo
{
    T bar;
};

template <typename U>
struct Foo<U &>
{
    U baz;
};
int main()
{
    int g = 0;
    Foo<short> a;
    Foo<int> b;
    Foo<int &> c{g};

Natvis:

<Type Name="Foo&lt;*&gt;">
  <DisplayString>partial specialization {baz}</DisplayString>
</Type>

<Type Name="Foo&lt;*&gt;" Priority="Low">
  <DisplayString>other specialization</DisplayString>
</Type>

Result: