是否可以 NATVIS 递归元组（可变参数模板）？

Posted 2023-02-22

【中文标题】是否可以 NATVIS 递归元组（可变参数模板）？

【英文标题】：Is it possible to NATVIS a recursive tuple (variadic template)?

【发布时间】：2016-04-20 12:28:18

【问题描述】：

我从这里实现了元组：https://voidnish.wordpress.com/2013/07/13/tuple-implementation-via-variadic-templates/

是否可以使用 NATVIS 将其可视化？我做到了

<Type Name="tuple">
  <DisplayString>()</DisplayString>  
</Type>

<Type Name="tuple&lt;*&gt;">
  <DisplayString>(_Myfirst)</DisplayString>
</Type>

如何获取多个类型的 _Myfirst 值，以获取

<Type Name="tuple&lt;*,*&gt;">
  <DisplayString>(_Myfirst, ???)</DisplayString>
</Type>

<Type Name="tuple&lt;*,*,*&gt;">
  <DisplayString>(_Myfirst, ???, ???)</DisplayString>
</Type>

等等？

【参考方案1】：

您必须稍微修改类型才能使其正常工作。需要的是base_type typedef。

即

// 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;
;

现在我们可以使用 natvis 声明递归地评估基本类型：

<!-- Handle empty tuples -->
<Type Name="tuple&lt;&gt;">
    <DisplayString>()</DisplayString>
    <Expand/>
</Type>

<!-- Handle a single parameter (this is also our terminator for recursion) -->
<Type Name="tuple&lt;*&gt;">
    <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&lt;*,*&gt;">
    <!-- 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>

结果如下：