C ++对齐的未来:通过价值传递? [英] The future of C++ alignment: passing by value?

问题描述

在阅读Eigen库文档时，我注意到某些对象无法通过值传递 . C ++ 11中是否有任何开发或计划中的开发可以使按值传递此类对象安全?

Reading the Eigen library documentation, I noticed that some objects cannot be passed by value. Are there any developments in C++11 or planned developments that will make it safe to pass such objects by value?

此外，为什么按值返回此类对象没有问题?

Also, why is there no problem with returning such objects by value?

推荐答案

他们可以在C ++ 11中做到这一点:

They could do this in C++11:

class alignas(16) Matrix4f
{
    // ...
};

现在，该类将始终在16字节的边界上对齐.

Now the class will always be aligned on a 16-byte boundary.

此外，也许我很傻，但这绝对不是问题.给定这样的课程:

Also, maybe I'm being silly but this shouldn't be an issue anyway. Given a class like this:

class Matrix4f
{
public:
    // ...
private:
    // their data type (aligned however they decided in that library):
    aligned_data_type data;

    // or in C++11
    alignas(16) float data[16];
};

编译器现在不得不在16字节边界上分配一个Matrix4f，因为那样会破坏它.类级别alignas应该是冗余的.但是过去，以某种方式知道我是错的.

Compilers are now obligated to allocate a Matrix4f on a 16-byte boundary anyway, because that would break it; the class-level alignas should be redundant. But I've been known to be wrong in the past, somehow.

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