Catching C++ Exceptions in D

[Walter Bright via Digitalmars-d]

We have a design now, driven by:

1. compatibility with best practice exceptions in C++ (i.e. never catch by 
value, etc.)

2. minimizing implementation difficulty

3. fitting in with D semantics

4. pushing as much as we can into the C++ compiler

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C++ exceptions cannot be thrown from D. If you must throw a C++ exception, write 
and call a C++ function to do it.

C++ rethrows as well need to be done by calling a C++ function to do it.

D code can only catch C++ exceptions declared as:

     extern (C++) class Identifier { ... }

Best practice in C++ is catching by const&, and D's classes fit right in with that.

At the exit of a catch clause, the destructor on the caught C++ exception will 
be run, as would be expected by C++ programmers.

Because of running the destructors, C++ exceptions cannot be caught in @safe code.

Function bodies cannot mix catching C++ and D exceptions. (The reason is C++ 
catch types need to be distinguished from D catch types, and the most 
straightforward method to deal with that is have a different 'personality' 
function for functions that catch C++ exceptions.) However, nested functions can 
catch different ones than their enclosing function.