Revamped concurrency API

[Jeremie Pelletier]

bearophile wrote:
> Jeremie Pelletier:
> 
>> I vote for a 'lent' qualifier to be implemented in the compiler.
> 
> You may be right, and Bartosz has explained me why and how to use lent. It sounds like a nice idea, but it has some costs too (in language complexity, for example). But I need to use such things in practice, in real (even small) programs to know/understand if I like and understand them enough.

I don't see how heavy that cost is since all of 
const/immutable/lent/shared are type qualifiers, the semantics are 
already there for const and immutable, and half there for shared.

I would also much prefer compiler implementations to be a bit more 
complex and implement lent/shared properly than push that complexity to 
user code. If we're trying to get rid of data races and deadlocks and 
whatnot, the last thing we want are complex implementations in 
library/user code because they lack the proper language primitives.

If we have just those two qualifiers, the rest of the concurrent models 
can be implemented entirely in the library.

> So I'd like to have an experimental version of D where such ideas (like lend, nonnull references, and few other things) can be tried, and if they are experimentally seen as not good (by me too), they can be discarded and removed. For me this is true for nonnull references, but such experimental need is even strong for lend.

D2 is already 'experimental' if you consider the state of shared right 
now :)

> It seem all the long discussion regarding nonnull references has gone nowhere. That has made me a little sad. Only a bit of flow analysis has being accepted, to cover certain cases of a specific bug case of uninitialized objects.

I never liked the Object vs Object? syntax, that would just create 
ambiguity with the ternary conditional. D already dropped the template 
syntax from C++ to drop the ambiguity with <> and comparison operators.

I wouldn't mind something like nonnull(Object), ie yet another type 
qualifier, although that would get cumbersome in a few cases like 
const(shared(nonnull(Object))) :o)

> Bye,
> bearophile