标准库容器最简单,性能较差的哈希类是什么?

In situations where performance can be ignored, some standard library containers still require a custom hash class for most of the types. Assume I have a type SomeType defined somewhere, I want to use std::unordered_set and I don't care about performance. The minimum I have to write is something like this:

template<typename T>
struct Hash42 {
  size_t operator()(T const& e) {return 42;}
};

std::unordered_set<SomeType, Hash42<SomeType>> s;

有更短的版本吗?是否在某个地方定义了通用哈希类?