activex.pp definition problem
lazarus / 67-Windows

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440bx · 2025-07-07 21:30

Hello,

In activex.pp there are a large number of GUID definitions that are
supposed to be constant but, they are not.

for instance, it is possible to do this:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i  
GUID_NULL.D1            := 1;  IID_IEnumConnections.D1 := 1; Known
GUIDs should not be changeable.

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Thaddy · 2025-07-08 04:54

Also the case in C++ btw... not a Pascal issue.
I guess you can declare these GUIDS as typed const, but in {$J-} state
which makes them immutable.
I thought you knew that:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
{$push}{$J-}const  myguid:TGUid =
'{77DE903C-1453-4622-93A0-1C46B74627B9}';{$pop}begin  myguid.d1 := 5;
 // Error: Can't assign values to const variable.end.It should be fine
to compile the whole interface section of the activex unit in forced
{$J-} state.
(If that is not already the case)
The guid ends up in .rodata and so is immutable:Code: ASM
 [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i .section
.rodata.n_TC_$P$PROGRAM_$$_MYGUID,"aw"        .balign 4.globl 
TC_$P$PROGRAM_$$_MYGUIDTC_$P$PROGRAM_$$_MYGUID:        .long  
2011074620        .short  5203,17954        .byte  
147,160,28,70,183,70,39,185  # same guid, but in decimal.# End asmlist
al_rotypedconstsMaybe @Marcov can check if this is the case and
otherwise protect the interface section with {$J-} ?
This should not otherwise affect the code. Must be done with
{$push}/{$pop}, though.

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440bx · 2025-07-08 05:54

Quote from: Thaddy on July 08, 2025, 06:54:30 amI thought you knew
that:
You actually thought ?... I hope you didn't experience too much pain.

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Thaddy · 2025-07-08 06:04

Nah...  Hope its solves the problem, though.

I did:
- around line 101 {$PUSH}{$WRITEABLECONST OFF} // start of GUID consts
- around line 189 {$POP} // end of GUID consts, alternatively around
line 4954 for the pop. Just above implementation.
That seems enough. Not really good with patching with GIT yet.
push/pop is necessary to avoid settings spill. 101/189 seems the most
"correct": least code affected.

I will leave that up to Marcov.
Just in case:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
packages/winunits-base/src/activex.pp | 4 ++-- 1 file changed, 2
insertions(+), 2 deletions(-) diff --git a/packages/winunits-
base/src/activex.pp b/packages/winunits-base/src/activex.ppindex
56dec102fe..2420a7e5bc 100644--- a/packages/winunits-
base/src/activex.pp+++ b/packages/winunits-base/src/activex.pp@@ -98,7
+98,7 @@    TOleColor           = OLE_COLOR;    POleColor           =
LPOle_Color;    HHandle             =
UINT_PTR;-+{$PUSH}{$WRITABLECONST OFF} CONST    GUID_NULL  : TGUID =
 '{00000000-0000-0000-0000-000000000000}';    IID_IPrint : TGUID =
'{B722BCC9-4E68-101B-A2BC-00AA00404770}';@@ -186,7 +186,7 @@   
IID_IOleCache2 : TGUID = '{00000128-0000-0000-C000-000000000046}';   
IID_IOleCacheControl : TGUID =
'{00000129-0000-0000-C000-000000000046}';    IID_IOleItemContainer :
TGUID = '{0000011C-0000-0000-C000-000000000046}';-+{$POP}       // bit
flags for IExternalConnection CONST Should be close to a correct
patch. (against trunk from today 10:00)

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nanobit · 2025-07-09 17:19

Unfortunately {$J+} is default in FPC,
whereas Delphi has the preferable default {$J-} since Delphi 6.

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Thaddy · 2025-07-09 19:05

See the bug report..... <sigh> And your statement about Delphi is not
true D7 behaves the same, D12.1 behaves the same.

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nanobit · 2025-07-09 19:37

Excerpt from Delphi 6 Developer’s Guide (Steve Teixeira):

QuoteMigrating from Delphi 5: Although compatibility between Delphi 5
and 6 is quite good, there are a few minor issues you should be aware
of as you make the move.
Writable Typed Constants
The default state of the $J compiler switch (also known as
$WRITEABLECONST) is now OFF,
where it was ON in previous versions. This means that attempts to
assign to typed constants will raise a compiler error unless you
explicitly enable this behavior using $J+.

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gues1 · 2025-07-09 20:27

In "Delphi 7 Object Pascal Language Guide" at page 5-43:

QuoteIn the default {$J-} compiler state, typed constants can not have
new values assigned
to them; they are, in effect, read-only variables.

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Thaddy · 2025-07-10 11:03

Yes. Hence my patch.