RAII and Deterministic Destruction

[ZombineDev via Digitalmars-d-learn]

On Wednesday, 26 August 2015 at 01:09:15 UTC, ZombineDev wrote:
> On Tuesday, 25 August 2015 at 22:35:57 UTC, Jim Hewes wrote:
>> Although C++ can be ugly, one reason I keep going back to it 
>> rather then commit more time to reference-based languages like 
>> C# is because I like deterministic destruction so much. My 
>> question is whether D can REALLY handle this or not. I've not 
>> been sure about this for some time so now I'm just going to 
>> come out and finally ask.
>>
>> I know about this RAII section in the documentation: 
>> http://dlang.org/cpptod.html#raii
>> But I don't believe that handles all cases, such as having 
>> classes as member variables of other classes. (Do the members 
>> get destructors called too?)
>>
>> Then there is std.typecons.Unique and  
>> std.typecons.RefCounted. With these, can I really get 
>> deterministic destruction for all cases like I would in C++?
>>
>> If so, it might be a good idea to emphasize this more in the 
>> documentation because I'd think people coming from C++ would 
>> be looking for this.
>>
>> Jim
>
> Structs in D behave like in C++ - they are created on the stack 
> (unless you use new or malloc), passed by value and are 
> automatically destroyed at the end of the scope. All their 
> members are destroyed recursively after the user defined 
> destructor is called.
>
> Just try it out in a toy program and see if it works as you 
> expect.

Classes on the other hand are reference types and are created on 
the garbage-collected heap by default (though you can do your own 
memory management). Similarly, structs created by new are also 
allocated on the GC heap. During collections the GC will call 
destructors, but it is not guaranteed and you should not rely on 
it. For example (depending on your GC usage and configuration) 
only a single collection may occur at the end of the program.