Oct 142017
 

Jeroen has submitted two enhancements to GExperts:

Thanks!

I am still working on the refactoring for the IDE form enhancements, but progress is slow, so the next release will probably take a while.

Sep 302017
 

A new test release of my dzDebugVisualizers for Delphi 2005, 2006 and 2007 is available. Apart from fixing an Access Violation when unloading the package I have added support for TDateTime and unquoted (multiline) strings to the Evaluate / Modify window:

In addition I have added a “Modifiers” button to the dialog which allows to add any of the supported display format specifiers to the expression.

Download that test release and tell me, what you think. What other data types would you like me to add? Are there any bugs?

Sep 032017
 

I was made aware that dzPrepBuild no longer works with .dof files. Since I don’t use it with Delhi 6 or 7 any more, I didn’t realize that myself. The bugfix was easy, just pass the correct parameter.

The new version is available from SourceForge. Note that, for whatever reason, SoureForge still claims that the latest download is version 1.3.0. You’ll have to select version 1.3.2 yourself. I hope that it is just a matter of time for SourceForge to update that link.

Sep 022017
 

David Heffernan commented on Girish Patil’s post on G+

But you should never make instance methods on value types that mutate the value.

Otherwise you can call such a method on an instance passed to a function as a const parameter.

Where “value types” in this case is meant to be an advanced record in Delphi.

I must admit that I am guilty of doing this and have of course lived to regret it. Here is an example:

type
  TDistance = record
  private
    FMillimetres: Int64;
  public
    function InMillimetres: Int64;
    function InMetres: Double;
    function InKm: Double;
    procedure AssignMetres(_Value: Double); // don't do this!
  end;

In case it isn’t obvious: This is an advanced record for storing a distance with a fixed resolution on 1 mm. The idea is to prevent cases where you have got a variable containing a distance but it isn’t immediately clear what unit is it using.

There are functions that return the value converted to metres and kilometres. And then there is a procedure AssignMetres which violates the rule that David stated:

procedure TDistance.AssignMetres(_Value: double);
begin
  FMillimetres := Round(_Value * 1000);
end;

On first glance, there is nothing wrong with this method. It simply assigns a new value to the record.

But now, consider this procedure that takes a const TDistance parameter:

procedure doSomething(const _Dist: TDistance);
begin
  // ...
  Dist.AssignMetres(5);
  // ...
end;

// ...
var
  SomeDist: TDistance;
begin
  SomeDist.AssignMetres(3);
  doSomething(SomeDist);
  // ...

The compiler won’t complain because calling methods of value types passed as const is allowed. But since the method has a side effect, setting the value of _Dist, it will not just change the value of _Dist inside the procedure but also the value of the variable passed to doSomething. The caller of course relies on that value to remain unchanged, because this is a const parameter after all. But, after the call to doSomething, the value of SomeDist now is 5m rather than 3m as originally assigned.

That’s what David meant with this comment.

This was bad enough, but there is another trap which I fell for. Consider this class that has a property Length of the type TDistance:

 type
  TCar = class
  private
    FHasChanged: boolean;
    FLength: TDistance;
    procedure SetLength;
  public
    property Length: TDistance read GetLength write SetLength;
    property HasChanged: read FHasChanged;
  end;
// ...
function TCar.GetLength: TDistance;
begin
  Result := FLength;
end;

procedure TCar.SetLength(const _Value: TDistance);
begin
  FHasChanged := True;
  FLength := _Value;
end;

Again, nothing seems to be wrong here. The SetLength property setter, in additon to setting the FLength field also sets the FHasChanged field to True which supposedly is read later on to determine whether any changes have to be saved somewhere. You could probably argue that the property getter for Length is not necessary, but who knows, it might become necessary later on.

It works fine too:

var
  MyCar: TCar;
  Dist: TDistance;
begin
  Dist.AssignMetres(4.5);
  MyCar := TCar.Create;
  try
    MyCar.Length := Dist;
    if MyCar.HasChanged then
      MyCar.SaveChanges;
  finally
    FreeAndNil(MyCar)
  end;

And then, probably years later, somebody thinks that the code above is unnecessarily complex and optimizes it like this:

var
  MyCar: TCar;
begin
  MyCar := TCar.Create;
  try
    MyCar.Length.AssignMetres(4.5);
    if MyCar.HasChanged then
      MyCar.SaveChanges;
  finally
    FreeAndNil(MyCar)
  end;

That’s a reasonable optimization. It looks much cleaner and gets rid of an unnecessary variable declaration. But it does not work!

Why? I’m glad you asked. Let’s have a look at what happens in this line:

MyCar.Length.AssignMetres(4.5);

It first calls the getter for the Length property, returning a copy of the FLenght field. Then it calls the AssignMetres method of that record, which changes the FMillimetres field of the record. Now, the question: What will be the value of the field MyCar.FLength? It will still be 0 (assuming the constructor of TMyCar does not initialize it otherwise), because we changed the value of the copy, not the value of the field. Also, MyCar.HasChanged will still be False, because the setter for Length has never been called.

So, advanced records should not have methods that change the record’s values. In the example, the solution would be something like this:

type
  TDistance = record
  private
    FMillimetres: Int64;
  public
    class function FromMetres(_Value: Double): TDistance; static;
    function InMillimetres: Int64;
    function InMetres: Double;
    function InKm: Double;
  end;

/// ...
class function TDistance.FromMetres(_Value: double): TDistance;
begin
  Result.FMillimetres := Round(_Value * 1000);
end;

So, a class function FromMetres would be used to return a new TDistance variable initialized to the given metres value.

And it would be used like this:

var
  MyCar: TCar;
begin
  MyCar := TCar.Create;
  try
    MyCar.Length := TDistance.FromMetres(4.5);
    if MyCar.HasChanged then
      MyCar.SaveChanges;
  finally
    FreeAndNil(MyCar)
  end;

The setter method for Length gets called does its thing. Everybody is happy. Until, of course, some smart ass like me thinks that an TDistance.AssignMetres would be a great idea …

Aug 202017
 

I have started to write some documentation on the internal workings of GExperts. For now, it covers only a very small part of the IDE form enhancements that GExperts provides. It is meant mostly for myself to get an overview of that part of the tool which has grown too large to understand at a single glance. But it might also help if somebody wants to contribute to that part.

Aug 122017
 

Donations for GExperts keep coming in. It’s more a trickle than a flood but hey, I’m not in it for the money. And please remember that I prefer other kinds of contributions over money.

I have used that money in turn for donations to

I would have liked to also donate to PuTTY and FileZilla but I found no way to do it.

(Yes, there is a donate link on the FileZilla SourceForge page but it doesn’t work.)

Jul 302017
 

The method of changing the order of the TabSheets in a PageControl in Delphi is not obvious. Apparently there is no drag and drop support (at least not in Delphi 2007). You have to change the PageIndex property. So, if you want to insert a new page, add it and then change its PageIndex to the insert position.

I smell an opportunity for a new GExperts Expert. Any takers?

EDIT: As Moreno Zenaro pointed out in a comment to my Google+ post, there is actually a GUI way of changing the order: Drag the TabSheet in the structure view.

Jul 292017
 

As I stated before I prefer good bug reports on GExperts over money any time. Philip von Melle kept testing and providing feedback even after I thought the issue was already solved.

The issue was that a Macro Template

(%SELECTION)

used on this code

// öäüß

procedure TForm1.FormCreate(Sender: TObject);
begin
  ShowMessage('TEST');
end;

while TEST was selected
generated code like this

// öäüß

procedure TForm1.FormCreate(Sender: TObject);
begin
  ShowMessage(''); (TEST)
end;

The reason again was improper use of positions and offsets into the editor buffer in conjunction with some Unicode characters above the code. So the insert position was calculated by 4 bytes too high, hence the macro code was inserted 4 characters behind the start of the original selection.

Jul 292017
 

Note to self: Do not use a watch entry like this while debugging GExperts:

GxOtaReadEditorTextToString(GxOtaGetEditReaderForSourceEditor(nil))

While this might seem very convenient it will sooner or later corrupt the current edit buffer or do something even worse, because, as a comment in ToolsApi states:

WARNING!!!
A IOTAEditReader should never be active at the same time as an IOTAEditWriter.

But having it as a disabled entry in the watch window, enable it to inspect the current content of the edit buffer, before disabling it again can be very useful.

Jul 012017
 

Since it became rather cumbersome to find the information on my Delphi IDE Explorer expert, which was scattered through multiple blog posts, I have now added a static page for it to my blog which I will keep up to date whenever I change anything in the expert. The sourceforge page now also points to this new page.

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