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Getting address of TSomeObject.AfterConstruction without using PVMT
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Author
Topic: Getting address of TSomeObject.AfterConstruction without using PVMT (Read 2573 times)
BrunoK
Sr. Member
Posts: 452
Retired programmer
Getting address of TSomeObject.AfterConstruction without using PVMT
«
on:
February 02, 2019, 10:58:16 am »
In the following procedure
Code: Pascal
[Select]
[+]
[-]
const
cCPEmptyMethod
:
Codepointer
=
nil
;
cCPAfterConstruction
:
Codepointer
=
nil
;
function
_InternalCreate
(
aSelf
:
TClass
;
aCreate
:
UIntPtr
)
:
TObject
;
var
lAfterConstruction
:
CodePointer
;
begin
Result
:
=
aSelf
.
Newinstance
;
if
Result
=
nil
then
exit
;
{ TObject.AfterConstruction does nothing, skip try / finally block thus
reducing code overhead for 90% of classes (?) }
lAfterConstruction
:
=
PVMT
(
aSelf
)
^
.
vAfterConstruction
;
// lAfterConstruction := @Result.AfterConstruction; // if activated, generates error
// fstobjcr.pp(96,25) Error: Incompatible types: got "<procedure variable type of procedure of object;Register>" expected "Pointer"
if
lAfterConstruction <> cCPAfterConstruction
then
if
lAfterConstruction <> cCPEmptyMethod
then
try
lAfterConstruction
:
=
nil
;
Result
.
AfterConstruction
;
lAfterConstruction
:
=
Result
;
finally
if
lAfterConstruction
=
nil
then
begin
// Failed AfterConstruction
Result
.
Destroy
;
Result
:
=
nil
;
end
;
end
;
end
;
I would like to replace PVMT(aSelf)^.vAfterConstruction with something like shown in the next line. But expressed like in snippet line 15, it gives error like in line 16.
Is there a way to get 'simply' (without having to go through complicated things that I already know how to do) a correct transtyping of lAfterConstruction := @Result.AfterConstruction.
Logged
howardpc
Hero Member
Posts: 4144
Re: Getting address of TSomeObject.AfterConstruction without using PVMT
«
Reply #1 on:
February 02, 2019, 11:57:39 am »
The following compiles. Whether it achieves what you want, I am not sure.
Code: Pascal
[Select]
[+]
[-]
uses
Forms
;
function
_InternalCreatedOK
(
aSelf
:
TClass
;
out anInstance
:
TObject
)
:
Boolean
;
var
lAfterConstruction
:
TProcedureOfObject
;
begin
Result
:
=
True
;
anInstance
:
=
aSelf
.
newinstance
;
if
anInstance
=
Nil
then
Exit
(
False
)
;
lAfterConstruction
:
=
@
anInstance
.
AfterConstruction
;
// if activated, generates error
try
if
Assigned
(
lAfterConstruction
)
then
lAfterConstruction
:
=
Nil
;
anInstance
.
AfterConstruction
;
finally
if
Assigned
(
lAfterConstruction
)
then
begin
// Failed AfterConstruction
anInstance
.
Destroy
;
anInstance
:
=
Nil
;
Result
:
=
False
;
end
;
end
;
end
;
Logged
ASerge
Hero Member
Posts: 2249
Re: Getting address of TSomeObject.AfterConstruction without using PVMT
«
Reply #2 on:
February 02, 2019, 12:06:39 pm »
May be this:
Code: Pascal
[Select]
[+]
[-]
{$MODE OBJFPC}
var
GAfterConstruction
:
CodePointer
=
nil
;
type
TAfterContruction
=
procedure
of
object
;
function
GetCodeOfAfterContruction
(
Method
:
TAfterContruction
)
:
CodePointer
;
inline
;
begin
Result
:
=
TMethod
(
Method
)
.
Code
;
end
;
function
_InternalCreate
(
ASelf
:
TClass
;
aCreate
:
UIntPtr
)
:
TObject
;
var
LAfterConstruction
:
CodePointer
;
begin
Result
:
=
ASelf
.
NewInstance
;
if
Result
=
nil
then
Exit
;
{ TObject.AfterConstruction does nothing, skip try / finally block thus
reducing code overhead for 90% of classes (?) }
LAfterConstruction
:
=
GetCodeOfAfterContruction
(
@
Result
.
AfterConstruction
)
;
if
LAfterConstruction
=
GAfterConstruction
then
// Skip default
else
Result
.
AfterConstruction
;
end
;
procedure
InitGAfterConstruction
;
var
Dummy
:
TObject
;
begin
Dummy
:
=
TObject
.
Create
;
try
GAfterConstruction
:
=
GetCodeOfAfterContruction
(
@
Dummy
.
AfterConstruction
)
;
finally
Dummy
.
Free
;
end
;
end
;
begin
InitGAfterConstruction
;
end
.
Logged
BrunoK
Sr. Member
Posts: 452
Retired programmer
Re: Getting address of TSomeObject.AfterConstruction without using PVMT
«
Reply #3 on:
February 02, 2019, 12:49:21 pm »
@howardpc, @ASerge
Thanks. As soon as my 3.0.6 is again functional (some little modifications beiing done), I'll test.
The objective is to have as little byte code as possible, otherwise what I'm trying to do do is useless (once again ...).
Logged
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Getting address of TSomeObject.AfterConstruction without using PVMT
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