nothrow by default

[Ola Fosheim Grøstad]

On Thursday, 9 January 2020 at 22:39:25 UTC, Johannes Pfau wrote:
> I don't know the details, but I guess that's the throw by value 
> / catch by reference idiom in C++. Not sure how it's actually 
> implemented.

It is implementation defined... in clang it uses a dedicated 
allocator function. But as you can see it does some optimizations:

https://llvm.org/docs/ExceptionHandling.html

> In addition to constructor + cache miss you'll also have to do 
> RTTI to match the object to the types in the catch handlers 
> (and for the downcast).

I assume that is how clang++ does it, but you don't _have_ to use 
RTTI structures. You could do it other ways.  But in C++ 
exceptions tend not to be used on the fast-path (meaning, used 
primarily for unexpected outcomes).