Template version of std::abs

问题

Here lists the current overloads of std::abs in C++. I'm wondering why not just define the following template and let go all the ugly C-style overloads?

template <typename T> inline
T abs(const T& v) { return v < 0 ? -v : v; }

回答1:

See LWG issue 2192. Currently, std::abs(x-y) < 2 fails if x and y are unsigned. This catches a subtle programming error. With the proposed change, it compiles but does entirely the wrong this. abs(3u-4u) would be much larger than 2, in fact it's UINT_MAX.

回答2:

This suffers the usual problem of matching everything.

An example of a type for which abs makes sense but this implementation does not is complex<double>.

回答3:

Because type 'T' can access any data type including char. So what are you expecting if someone will pass a char to the abs function. :)

来源：https://stackoverflow.com/questions/29411486/template-version-of-stdabs