c++ - What's the motivation behind having copy and direct initialization behave differently?

Question

Somewhat related to Why is copy constructor called instead of conversion constructor?

There are two syntaxes for initialization, direct- and copy-initialization:

A a(b);
A a = b;

I want to know the motivation for them having different defined behavior. For copy initialization, an extra copy is involved, and I can't think of any purpose for that copy. Since it's a copy from a temp, it can and probably will be optimized out, so the user can't rely on it happening - ergo the extra copy itself isn't reason enough for the different behavior. So... why?

Answer 1

Only a speculation, but I am afraid it will be hard to be more certain without Bjarne Stroustrup confirming how it really was:

It was designed this way because it was assumed such behaviour will be expected by the programmer, that he will expect the copy to be done when = sign is used, and not done with the direct initializer syntax.

I think the possible copy elision was only added in later versions of the standard, but I am not sure - this is something somebody may be able to tell certainly by checking the standard history.