Performance improvements for D / DMD compiler.

[Christian Kamm]

>>  There's another aliasing case:
>>  LargeStruct s;
>> foo(s);
>> ... here some other thread modifies s ...

Okay, I can see that this could result in unexpected behaviour. The idea  
of determining whether to copy or not during compile time was not a good  
one at all. What sparked this suggestion was exactly the situation Bill  
Baxter described:

> The question is how can we write functions in D that take big structs as  
> parameters in such a way that it is:
> A) efficient and
> B) guaranteed not to change the caller's value

If inout is used, it doesn't guarantee B) and even worse: I'm lying to  
anyone reading the function signature. A pointer will also require  
additional documentation to keep users from wondering whether their data  
is changed or not. Making the struct a class is not an option because of  
A).

Maybe it's just time to accept that D just doesn't do const the C++ way  
and B) can't be expressed.

Christian