Migrating an existing more modern GC to D's gc.d

[Steven Schveighoffer]

On 4/10/18 4:37 AM, David Bennett wrote:
> On Tuesday, 10 April 2018 at 08:10:32 UTC, Jonathan M Davis wrote:
>>
>> Yes. They expect it to work, and as the language is currently 
>> designed, it works perfectly well. In fact, it's even built into the 
>> language. e.g.
>>
>>     int[] foo() pure
>>     {
>>         return [1, 2, 3, 4];
>>     }
>>
>>     void main()
>>     {
>>         immutable arr = foo();
>>     }
>>
>> compiles thanks to the fact that the compiler can guarantee from the 
>> signature of foo that its return value is unique.
>>
> 
> Oh is that run at runtime? I thought D was just smart and did it using 
> CTFE.

Well, D could be smart enough and call a runtime function that says it's 
moving data from thread-local to shared (or vice versa).

> 
>>
>> We also have std.exception.assumeUnique (which is just a cast to 
>> immutable) as a way to document that you're guaranteeing that a 
>> reference to an object is unique and therefore can be safely cast to 
>> immutable.
>>
> 
> Can't say I've used std.exception.assumeUnique, but I guess other people 
> have a use for it as it exists.
> 
> Would be nice if you could inject type checking information at compile 
> time without effecting the storage class. But thats a bit OT now.

assumeUnique is a library function, it could be instrumented to do the 
right thing.

I think it's possible to do this in D, but you need language support.

-Steve