为什么不允许double作为非类型模板参数？ [英] Why is double not allowed as a non-type template parameter?

问题描述

2003年-是， 2003 -Vandervoorde和Josuttis在他们的书 C ++模板（第40页）中写道：

In 2003 - yes, 2003 - Vandervoorde and Josuttis wrote this in their book "C++ Templates" (p. 40):

不能将浮点文字（和简单的常量浮点表达式）用作模板参数是有历史原因的。由于没有严重的技术挑战，因此在将来的C ++版本中可能会支持。

Not being able to use floating-point literals (and simple constant floating-point expressions) as template arguments has historical reasons. Because there are no serious technical challenges, this may be supported in future versions of C++.

但这仍然行不通，甚至在C ++ 11下：

But this still doesn't work, even under C++11:

template<double D> //error
void foo() {}

为什么不添加？ p>

Why was this not added?

推荐答案

我一直认为它与相互匹配的实现有关。就像这两个实例相同还是不同：

I had always assumed it had to do with matching implementations against each other. Like are these two instances the same or different:

template class foo<10./3.>
template class foo<1./3 * 10.>

它们可能不会生成相同的双精度表示形式，因此编译器可能会将它们视为不同的类。然后您就无法将它们彼此分配，等等。

They may not generate the same double-precision representation, so the compiler might think of them as different classes. Then you couldn't assign them to each other, etc.

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