自包含，STL兼容的std :: vector实现

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它们的实现似乎不必要的复杂（检查源和），但主要的想法是封装进入 std :: vector 和一个薄包装的类型：

  #include< vector> 
 
 template< typename T> 
 struct wrapper：public T 
 {
 wrapper（）{} 
 wrapper（const T& rhs）：T（rhs）{} 
}; 
 
 struct __declspec（align（64））S 
 {
 float x，y，z，w; 
}; 
 
 int main（）
 {
 std :: vector<包装物> v; // OK，no C2719 error 
 return 0; 
}

关于Eigen的实现，我必须承认我不太明白

为什么需要 Eigen :: aligned_allocator_indirection ，

为什么他们需要对 EIGEN_WORKAROUND_MSVC_STL_SUPPORT ，

中的算术类型进行例外处理，为什么需要定义所有这些构造函数和运算符 Eigen :: workaround_msvc_stl_support ，

或为什么需要重新定义 resize 在其 std :: vector 的部分专门化 Eigen :: aligned_allocator_indirection allocator ...

欢迎链接。关键是，这个技巧完美的（就我所知），我没有看到任何错误，除了可能从轻微的无礼。

The implementation of std::vector that ships with Visual Studio 2010 and earlier versions has a well known particularity: the resize method has the following signature (C++03-compliant):

void resize(size_type new_size, value_type value);

instead of the C++11-compliant signature that's been used by the majority of other STL implementations (like gcc's STL or STLport) long before C++11:

void resize(size_type new_size, const value_type& value);

The problem with the first variant is that, in some situations, it will fail to compile if value_type has an alignment specification:

struct __declspec(align(64)) S { ... };
std::vector<S> v;  // error C2719: '_Val': formal parameter with __declspec(align('64')) won't be aligned

This is a well known problem with no satisfactory workaround apart from using a different implementation of std::vector.

I'm looking for a well-written, well-tested, self-contained and STL-compatible implementation of std::vector with a MIT-style licence that I could drop into my project as a container of choice for aligned types.

I considered extracting it from STLport or gcc's STL but, being fully standard-compliant, they're both large with many non-trivial dependencies.

(I would be perfectly happy with an implementation of a reasonable subset of std::vector that would only support push_back, clear, capacity, size, reserve, resize, swap and array indexing.)

Any ideas?

解决方案

The guys behind the Eigen library seem to have found a nice workaround for the problem of storing "overly-aligned types" (as Stephan T. Lavavej call them) into a std::vector as implemented in Visual Studio's STL.

Their implementation seems unnecessary complicated (check the sources here and here) but the main idea is to encapsulate the type that goes into the std::vector with a thin wrapper:

#include <vector>

template <typename T>
struct wrapper : public T
{
    wrapper() {}
    wrapper(const T& rhs) : T(rhs) {}
};

struct __declspec(align(64)) S
{
    float x, y, z, w;
};

int main()
{
    std::vector< wrapper<S> > v;  // OK, no C2719 error
    return 0;
}

About the implementation in Eigen, I must admit I don't quite understand

why they need Eigen::aligned_allocator_indirection,
why they need to make an exception for arithmetic types in EIGEN_WORKAROUND_MSVC_STL_SUPPORT,
why they need to define all these constructors and operators in Eigen::workaround_msvc_stl_support,
or why they need to redefine resize in their partial specialization of std::vector for the Eigen::aligned_allocator_indirection allocator...

Clues welcome. The point is, this trick works perfectly (as far as I can tell) and I don't see anything wrong with it, apart maybe from the slight inelegance.

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