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digitalmars.D.learn - Hidden members of Class objects

reply Carl Sturtivant <sturtivant gmail.com> writes:
I notice that a class with no data members has a size of two 
words (at 64 bits). Presumably there's a pointer to a table of 
virtual functions, and one more. Is the Vtable first?

A COM class that inherits from IUnknown and has no data members 
has a size of three words, presumably as before plus something 
that ordinarily is in the Vtable but can't be for a COM object as 
it has its own layout of that.

What is actually in these objects using that space?
Mar 06
parent reply "H. S. Teoh" <hsteoh qfbox.info> writes:
On Wed, Mar 06, 2024 at 11:39:13PM +0000, Carl Sturtivant via
Digitalmars-d-learn wrote:

 I notice that a class with no data members has a size of two words (at
 64 bits). Presumably there's a pointer to a table of virtual
 functions, and one more. Is the Vtable first?


[...]

 What is actually in these objects using that space?


In D, there's a pointer to the vtable and another pointer to a Monitor
object (used for synchronized methods).  There was talk about getting
rid of the Monitor field years ago, but nothing has happened yet.


T

-- 
MAS = Mana Ada Sistem?
Mar 06
parent reply Carl Sturtivant <sturtivant gmail.com> writes:
On Wednesday, 6 March 2024 at 23:45:00 UTC, H. S. Teoh wrote:

 In D, there's a pointer to the vtable and another pointer to a 
 Monitor object (used for synchronized methods).  There was talk 
 about getting rid of the Monitor field years ago, but nothing 
 has happened yet.


Very interesting: is the monitor field ever touched by compiled D 
code at any point nowadays? Or is it just vestigial?
Mar 06
next sibling parent kinke <noone nowhere.com> writes:
On Thursday, 7 March 2024 at 00:28:17 UTC, Carl Sturtivant wrote:

 On Wednesday, 6 March 2024 at 23:45:00 UTC, H. S. Teoh wrote:

 In D, there's a pointer to the vtable and another pointer to a 
 Monitor object (used for synchronized methods).  There was 
 talk about getting rid of the Monitor field years ago, but 
 nothing has happened yet.


 Very interesting: is the monitor field ever touched by compiled 
 D code at any point nowadays? Or is it just vestigial?


It's (lazily initialized and) used by the 
`synchronized(<expression>)` statement (§3 of 
https://dlang.org/spec/statement.html#synchronized-statement) and 
the mentioned `synchronized` class methods 
(https://dlang.org/spec/class.html#synchronized-methods).
Mar 06
prev sibling parent reply "Richard (Rikki) Andrew Cattermole" <richard cattermole.co.nz> writes:
On 07/03/2024 1:28 PM, Carl Sturtivant wrote:

 On Wednesday, 6 March 2024 at 23:45:00 UTC, H. S. Teoh wrote:

 In D, there's a pointer to the vtable and another pointer to a Monitor 
 object (used for synchronized methods).  There was talk about getting 
 rid of the Monitor field years ago, but nothing has happened yet.


 
 Very interesting: is the monitor field ever touched by compiled D code 
 at any point nowadays? Or is it just vestigial?


Yes its opt-in. https://dlang.org/spec/statement.html#synchronized-statement
Mar 06
next sibling parent cc <cc nevernet.com> writes:
On Thursday, 7 March 2024 at 00:38:30 UTC, Richard (Rikki) Andrew 
Cattermole wrote:

 On 07/03/2024 1:28 PM, Carl Sturtivant wrote:

 On Wednesday, 6 March 2024 at 23:45:00 UTC, H. S. Teoh wrote:

 In D, there's a pointer to the vtable and another pointer to 
 a Monitor object (used for synchronized methods).  There was 
 talk about getting rid of the Monitor field years ago, but 
 nothing has happened yet.


 
 Very interesting: is the monitor field ever touched by 
 compiled D code at any point nowadays? Or is it just vestigial?


 Yes its opt-in. 
 https://dlang.org/spec/statement.html#synchronized-statement


I've stumbled over the Monitor/etc sometimes writing 
serialization, RPC, LUA etc modules iterating over class members, 
looking for UDAs, after trying to separate everything out using 
isFunction/isTemplate/etc, on top of dealing with overload 
spaghetti, I now just explicitly do something dumb like this to 
get those edge cases out of the way:

```d
static foreach (sym; __traits(allMembers, T))
static if 
(!["__ctor","__dtor","__xdtor","Monitor","factory"].canFind(sym)) 
{{
	...
```
Mar 07
prev sibling parent Carl Sturtivant <sturtivant gmail.com> writes:
On Thursday, 7 March 2024 at 00:38:30 UTC, Richard (Rikki) Andrew 
Cattermole wrote:

 Yes its opt-in. 
 https://dlang.org/spec/statement.html#synchronized-statement


As you mentioned in another thread there's handy ABI 
documentation for classes and interfaces just here 
[https://dlang.org/spec/abi.html#classes](https://dlang.org/sp
c/abi.html#classes) that spells out the story.
Mar 26