"case style" statements for elements of a set variable?

[741]

This is what I'm trying to do.

Code: Pascal  [Select][+][-]

1. procedure TfrmMain.pbxGridMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
2. begin
3.   case Shift of  //Invalid code, but shows what I'd like to achieve
4.      ssLeft: sbrImagZ.Panels[1].Text := 'Left Down';
5.      ssRight: sbrImagZ.Panels[1].Text := 'Right Down';
6. ...//etc
7.   end;

I can see it is not valid because the set 'Shift' may contain more than one element. Would I have to use

Code: [Select]

if ssLeft in Shift then //...Maybe theere is a neater way?

[Martin_fr]

The short answer is: You can't use case. You have to use the "if" statements.


The long answer is, if you want to go on a tricky, slippery path and use some hacked together code .... You can get case do to the job. But as you said "there can be multiple enums set". The "case" will see each combination as a different option.

I do _ NOT _ recommend the below. Do not use it.
The below is for fun of hacking the code, not for use in any app.

It will probably break, if you use any options that change the size of sets.
It also depends on the CPU (big endian vs little endian).

Code: Pascal  [Select][+][-]

1. // Example of really bad code
2. var
3.   c: TShiftState;
4. begin
5.   c := [ssRight];
6.   // Example of really bad code
7.   case cardinal(c) of
8.     1 << (ord(ssLeft))  : writeln('left');
9.     1 << (ord(ssRight)) : writeln('right');
10.     (1 << (ord(ssLeft))) or
11.     (1 << (ord(ssRight))) : writeln('both');
12.     otherwise
13.       writeln('left/right may still be set, but combined with other enums in the set');
14.   end;
15. end;
16.  

[cdbc]

Hi
There is an old trick, from before one could put strings in a 'case' statement...
In unit 'StrUtils' look for this:

Code: Pascal  [Select][+][-]

1. function AnsiIndexStr(const AText: AnsiString; const AValues: array of AnsiString): Integer;
2. begin
3.   for result:=low(AValues) to High(Avalues) do
4.      if (avalues[result]=AText) Then
5.        exit;                                    // make sure it is the first val.
6.   result:=-1;
7. end;

Normally you'd use it like this:

Code: Pascal  [Select][+][-]

1. ...
2.   case AnsiIndexStr('Two',['One','Two','Three','Four']) of
3.     0: showmessage('One');
4.     1: showmessage('Two');
5.     ... etc
6.   end;
7. ...

MeThinks it would be a small, short task to create a function for TShiftState 
Then you could use 'case' for that too 
eta: !!! Beware: the above function ONLY returns the first occurrence -- Well in hindsight it's probably a shijty solution, forget 'bout it...
Regards Benny

[jamie]

To explain it better, TShiftState is a SET with means it represents multiple set values into one.

A Case only works with single values like an ENUMERATOR where the object holding the definition holds only one item per case. In this situation, the SET can hold multiple states as indicated.

 So using the IN operator is normally the chosen way.

Jamie

[jamie]

Code: Pascal  [Select][+][-]

1. procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
2.   Y: Integer);
3. begin
4.   Case LongBool(LongInt(Shift) and ((Ord(ssCtrl)+1) Shl Ord(ssCtrl))) Of
5.    true:Caption := DateTimeTostr(Now);
6.    False:Caption := 'Control not down';
7.   End;
8. end;                                
9.  

To give you a perspective of what it would be like to use a case statement for just one item in the set.

Jamie

[jamie]

But

Code: Pascal  [Select][+][-]

1. procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
2.   Y: Integer);
3.  Var
4.    I :TShiftStateEnum;
5.    S:String;
6. begin
7.   S:= 'Nothing pressed';
8.   For I in Shift do
9.    Case I of
10.      ssShift :S := 'Shift';
11.      ssAlt   :S := 'Alt Key';
12.      ssCtrl  :S:= 'Control Key';
13.    end;
14.   Caption := S;
15. end;                                      
16.  
17.  

jamie

[d2010]

But

Code: Pascal  [Select][+][-]

1. procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
2. end;                                      
3.  

jamie

Code: Pascal  [Select][+][-]

1. procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,  Y: Integer);
2.  Var
3.    I :TShiftStateEnum;
4.    S:String;
5. begin
6.   S:='';
7.   For I in Shift do
8.    Case I of
9.      ssShift :S := s+'Shift+';
10.      ssAlt   :S := s+'Alt Key+';
11.      ssCtrl  :S:= s+'Control Key+';
12.    end;
13.   if length(s)<03 then caption:='Nothing pressed ! Please you try again<<case style" statements for elements of a set variable?'   else
14.      Caption := copy(S,1,length(s)-0001);
15. end;                                      
16.  

[741]

Glad I asked, lots of interesting replies and looks like a solution too
Thanks one & all.

[ASerge]

Code: Pascal  [Select][+][-]

1. uses TypInfo;
2.  
3. procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
4. var
5.   P: PTypeInfo;
6. begin
7.   P := TypeInfo(Shift);
8.   Caption := SetToString(P, @Shift, True);
9. end;

[jamie]

Code: Pascal  [Select][+][-]

1. uses TypInfo;
2.  
3. procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
4. var
5.   P: PTypeInfo;
6. begin
7.   P := TypeInfo(Shift);
8.   Caption := SetToString(P, @Shift, True);
9. end;

You are going to the Dark Side with all this high-level STUFF!!!!