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digitalmars.D.learn - Details on how aggregates are constructed with `new` and later

reply Per =?UTF-8?B?Tm9yZGzDtnc=?= <per.nordlow gmail.com> writes:
I want to understand how calls to `new` for classes and structs 
are lowered by the compiler and druntime to a GC-allocation 
(specifically how the `ba`-argument bits are determined) followed 
by an initialization using default constructor or via a 
user-defined constructor called using arguments to `new`. And how 
this is related to the trait `hasElaborateConstructor` for both 
`classes` and `structs`.

I also want to understand how manually defined constructors and 
destructors affect the setting of the GC finalizer for a given 
aggregate type. And how this is related to the trait 
`hasElaborateDestructor` for both `classes` and `structs`.

Where's the dmd and druntime code that handles these steps?
Oct 08 2018
next sibling parent Nicholas Wilson <iamthewilsonator hotmail.com> writes:
On Monday, 8 October 2018 at 11:19:40 UTC, Per Nordlöw wrote:

 I want to understand how calls to `new` for classes


see _d_newclass


 and structs are lowered by the compiler and druntime to a 
 GC-allocation (specifically how the `ba`-argument bits are 
 determined) followed by an initialization using default 
 constructor or via a user-defined constructor called using 
 arguments to `new`. And how this is related to the trait 
 `hasElaborateConstructor` for both `classes` and `structs`.


Memory is allocated, .init (for classes this comes from 
typeid(T).initializer)
  is copied over the memory and then the constructor is run.


 I also want to understand how manually defined constructors and 
 destructors affect the setting of the GC finalizer for a given 
 aggregate type. And how this is related to the trait 
 `hasElaborateDestructor` for both `classes` and `structs`


For classes the typeid(T).destructor is called on the class, for 
structs I'm not sure.


 Where's the dmd and druntime code that handles these steps?


should be src/rt/lifetime.d IIRC
Oct 08 2018
prev sibling parent Stanislav Blinov <stanislav.blinov gmail.com> writes:
On Monday, 8 October 2018 at 11:19:40 UTC, Per Nordlöw wrote:

 And how this is related to the trait `hasElaborateConstructor` 
 for both `classes` and `structs`.


There's no such trait as far as I'm aware. If there were, it'd 
likely be checking for the presence of a '__ctor' member. Thing 
is, it can't be generic because ctors may be templates, the best 
that can be done is checking if `T` is constructible with some 
arguments `Args`.


  And how this is related to the trait `hasElaborateDestructor` 
 for both `classes` and `structs`.


It isn't. The trait literally just checks if the compiler has 
generated a '__dtor' member, and it doesn't do so for classes at 
all.
Oct 08 2018