在我的一个项目中，我有以下类模板层次结构：
template <typename FruitType, typename ParentFilterType = void>
class filter;
template <typename FruitType> // Specialization when no parent filter is needed
class filter<FruitType, void>;
其中 FruitType 可以是任何内容。假设它是 apple、banana 或 orange 之一。
所以基本上，filter 可以有自己的父 filter 类型。
我无法控制过滤代码：它必须保持原样。
用户代码通常如下所示：
filter<apple, filter<banana, filter<orange> > > my_apple_filter;
显然，这有点冗长。我想知道是否有可能获得更具可读性的东西。类似于：
complex_filter<apple, banana, orange>::type my_apple_filter;
其中 complex_filter::type 将解析为 filter > >。
我尝试将complex_filter作为一个struct模板，其中包含typedef，但到目前为止没有成功。模板参数的数量应该是可变的（例如，从 1 到 5）。
您是否曾经需要过类似的东西？我怎么能这么做呢？
（不幸的是，我无法使用 C++0x，但如果有更好的解决方案，请随时发布它，因为知道它总是很高兴）
谢谢。
In one of my projects, I have the following class template hierarchy :
template <typename FruitType, typename ParentFilterType = void>
class filter;
template <typename FruitType> // Specialization when no parent filter is needed
class filter<FruitType, void>;
Where FruitType can be anything. Let's say it is one of apple, banana or orange.
So basically, a filter can have its own parent filter type.
I have no control over the filter code: it must remain as it is.
The user code usually looks like:
filter<apple, filter<banana, filter<orange> > > my_apple_filter;
Obviously, this is a bit verbose. I wondered if it is possible to get something more readable. Something like:
complex_filter<apple, banana, orange>::type my_apple_filter;
Where complex_filter<apple, banana, orange>::type would resolve to filter<apple, filter<banana, filter<orange> > >.
I tried with complex_filter being a struct template with a typedef inside but had no success so far. The number of template parameters should be variable (from, say, 1 to 5).
Have you ever needed something similar ? How could I do that ?
(I unfortunately cannot use C++0x but if there is a nicer solution with it, feel free to post it as it is always good to know)
Thank you.
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在 C++0x 中，它将是可变参数模板。
如果没有 C++0x，您可以简单地使用大量参数，并提供默认值。
然后可以根据需要使用它，如果您需要更多参数，则必须手动扩展它。
In C++0x, it would be variadic template.
Without C++0x, you can simply use a large list of parameters, with defaults supplied.
This can then be used as you wanted, and you will have to extend it manually if you ever want more parameters.
你尝试过的应该有效，有点：
what you tried should work, sort of: