On 5/18/21 3:04 PM, Ola Fosheim Grostad wrote:
> On Tuesday, 18 May 2021 at 18:51:40 UTC, Paul Backus wrote:
>> On Tuesday, 18 May 2021 at 17:53:20 UTC, Ola Fosheim Grostad wrote:
>>>
>>> Does a delegate do anything more than retaining a pointer to the stack record?
>>> Anyway, it should not escape the scope it references. So escape analysis is your friend.
>>
>> The compiler does escape analysis and pre-emptively allocates any variables that escape through closures on the GC heap.
>>
>> The bug here is that, for variables declared in loop bodies, the compiler *should* allocate a new copy on the heap for each loop iteration, but instead it only allocates one copy that's reused across all iterations.
> 
> Yes, absolutely. I dont use delegates much (well, I did in D1 but that is a long time ago), but the difference between point 3 and point 7 in the language reference is tricky to grasp. So if you bind a local function to a delegate parameter you dont take a closure, but if you assign to a delegate variable you get a closure?
> 
> "7. Delegates to non-static nested functions contain two pieces of data: the pointer to the stack frame of the lexically enclosing function (called the context pointer) and the address of the function."

There's also the issue that if you have a scoped variable that has a destructor, the value will be destroyed (and probably unusable) if you call the delegate from outside the scope.

-Steve

On Tuesday, 18 May 2021 at 19:20:55 UTC, Steven Schveighoffer wrote:
> On 5/18/21 3:04 PM, Ola Fosheim Grostad wrote:
> There's also the issue that if you have a scoped variable that has a destructor, the value will be destroyed (and probably unusable) if you call the delegate from outside the scope.

Ouch. Ok, so in OO languages like Simula, all scopes are heap-closures and there is no stack, which kinda changes the game. I guess Javascript does the same conceptually but the JIT perhaps extracts uncaptured variables and puts those on a stack as an optimization? (My guess)

But how does a function with a delegate parameter know if it is safe to store the delegate or not?