Access to vector underlying data in .natvis files for Visual Studio ImageWatch plugin

The problem

Similar to this question, I am trying to use the ImageWatch plugin for my own defined type MyImageClass. ImageWatch is a Visual Studio Plugin that allows you to view Images in a graphical representation while debugging code. You can write .natvis files to add support for custom defined classes.

struct MyImageClass
{
  uint32_t width;
  uint32_t height;
  std::vector<char> image_data;
}

The ImageWatch plugin expects a char* type for the image data, however I am storing my data in a std::vector<char>. My .natvis file, is quite simple, (you can skip it, only for completeness)

<?xml version="1.0" encoding="utf-8"?>
<AutoVisualizer xmlns="http://schemas.microsoft.com/vstudio/debugger/natvis/2010"> 
  <UIVisualizer ServiceId="{A452AFEA-3DF6-46BB-9177-C0B08F318025}" Id="1"
            MenuName="Add to Image Watch"/> 
  <Type Name="MyImageClass">
    <UIVisualizer ServiceId="{A452AFEA-3DF6-46BB-9177-C0B08F318025}" Id="1" />
  </Type>

  <Type Name="MyImageClass">
    <Expand>
      <Synthetic Name="[type]">
        <DisplayString>UINT8</DisplayString>
      </Synthetic>
      <Item Name="[channels]">1</Item>
      <Item Name="[width]">width</Item>
      <Item Name="[height]">height</Item>
      <Item Name="[planes]">1</Item>
      <Item Name="[data]">image_data</Item>
      <Item Name="[stride]">width</Item>
    </Expand>
  </Type>  
</AutoVisualizer>

But the following line I am struggeling with <Item Name="[data]">image_data</Item>. The image data assignment does not work, I cannot see the image in the viewer. Instead I get the message "invalid". Clearly, this is because image_data is a std::vector<char> and not char*.

What I have tried

I have tried many different things inside the <Item Name="[data]">image_data</Item> tag to access the vectors underlying char* data pointer, but none work:

image_data
image_data.data() Apparently no functions may be called in .natvis Files, Natvis output: Error: Side effects are not supported in this context.
image_data._Myfirst (Similar to here Section "ArrayItems Expansion") Natvis output: Error: a pointer to a bound function may only be used to call the function

What works, but isn't the ideal solution

As a workaround and to see if my data is correct I have added a char* to the struct and then assign it the vectors underlying data.

struct MyImageClass
{
  uint32_t width;
  uint32_t height;
  std::vector<char> image_data;
  char* image_data_ptr;
};

and then

image_data_ptr = image_data.data();

The .natvis file is changed accordingly

<Item Name="[data]">image_data_ptr</Item>

This works, and I can see the image in ImageWatch. However, I would hate to introduce an extra variable, only for the purpose of the VS debugger. Any help is highly appreciated.

Solution

So apparently the data of the vector can be analyzed the following way:

<Item Name="[data]">image_data._Mypair._Myval2._Myfirst</Item>

I found this out by analyzing the natvis debug output for a different vector.

Edit:

As I realized, this is implementation specific. The above solution works well under VS2015. In VS 2012, the solution which didn't work above

<Item Name="[data]">image_data._Myfirst</Item>

works quite well.