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Mailing lists / fpc-pascal / 2006-12

Boolean case statement

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Terry Kemp

Hi All

how do you do a case statement on a record of booleans e.g...

Type
 EngModeRec = Record
  ManualOp: Boolean;
  LeakTest: Boolean;
  DrainFlush: Boolean;
 end;
var
 EngMode: EngModeRec;

I want to have...

 Case True of
  EngMode.ManualOp: ManualOpRun;
  EngMode.LeakTest: LeakTestRun;
  EngMode.DrainFlush: DrainFlushRun;
 end;

but of course this wont work :(

Thanks Terry

errors...
Running tool: Build Arm

Target OS: Linux for ARM
Compiling mflow.pp
2 68/832 Kb Used
Compiling mrun.pp
Compiling mgldec.pp
100 4.039/4.736 Kb Used
Assembling mgldec
Compiling mstages.pp
100 4.158/4.864 Kb Used
Compiling mglproc.pp
100 5.166/5.920 Kb Used
200 5.417/6.336 Kb Used
300 5.712/6.560 Kb Used
Assembling mglproc
200 5.418/6.720 Kb Used
300 5.598/6.848 Kb Used
400 5.783/6.912 Kb Used
500 5.954/7.008 Kb Used
600 6.163/7.168 Kb Used
Assembling mstages
100 7.653/9.120 Kb Used
200 8.105/9.472 Kb Used
mrun.pp(289,19) Error: Constant Expression expected mrun.pp(290,19) Error: Constant Expression expected mrun.pp(290,19) Error: duplicate case label
mrun.pp(291,21) Error: Constant Expression expected mrun.pp(291,21) Error: duplicate case label
300 8.383/9.472 Kb Used
mrun.pp(384) Fatal: There were 5 errors compiling module, stopping mrun.pp(6,6) Fatal: Compilation aborted

Exited: 256

Vincent Snijders
to Terry Kemp
Terry Kemp wrote 25 lines
Hi All how do you do a case statement on a record of booleans e.g... Type EngModeRec = Record ManualOp: Boolean; LeakTest: Boolean; DrainFlush: Boolean; end; var EngMode: EngModeRec; I want to have... Case True of EngMode.ManualOp: ManualOpRun; EngMode.LeakTest: LeakTestRun; EngMode.DrainFlush: DrainFlushRun; end; but of course this wont work :( 
You cannot use it like that. You would have to use an nested if then
statement like:

if EngMode.ManualOp then ManualRun
else if EngMode.ManualOp then LeakTest
else etc.

I would use an enum:

type
   TEngMode = (emManualOp, emLeakTest, emDrainFlush);
var
   EngMode : TEngMode;
case EngMode of
   emManualOp: ManualRun;
   emLeakTest: LeakTestRun;
   emDrainFlush: DrainFlushTest;
end;

if several EngMode can occur at the same time (like can happen with EngModeRec) you can use

type
   TEngModeSet = set of TEngMode;

But then you cannot use case anymore to do the tests.

HTH,
Vincent

Daniël Mantione
to Terry Kemp: Hi All how do you do a case statement on a record of booleans e.g... Type EngModeRec =…

Op Wed, 6 Dec 2006, schreef Terry Kemp:

Show quoted text 23 lines
Hi All how do you do a case statement on a record of booleans e.g... Type EngModeRec = Record ManualOp: Boolean; LeakTest: Boolean; DrainFlush: Boolean; end; var EngMode: EngModeRec; I want to have... Case True of EngMode.ManualOp: ManualOpRun; EngMode.LeakTest: LeakTestRun; EngMode.DrainFlush: DrainFlushRun; end; but of course this wont work :(
with engmode do
  begin
    if manualop then
      manualoprun;
    if leaktest then
      leaktestrun;
    if drainflushop then
      drainflushrun;
  end;

Daniël Mantione

Steve Williams
to Terry Kemp: Hi All how do you do a case statement on a record of booleans e.g... Type EngModeRec =…
Terry Kemp wrote 24 lines
Hi All how do you do a case statement on a record of booleans e.g... Type EngModeRec = Record ManualOp: Boolean; LeakTest: Boolean; DrainFlush: Boolean; end; var EngMode: EngModeRec; I want to have... Case True of EngMode.ManualOp: ManualOpRun; EngMode.LeakTest: LeakTestRun; EngMode.DrainFlush: DrainFlushRun; end; but of course this wont work :(

Of course it won't work. It is invalid syntax. You need to test each member using an if statement.

if EngMode.ManualOp then ManualOpRun;
if EngMode.LeakTest then LeakTestRun;
if EngMode.DrainFlush then DrainFlushRun;
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Terry Kemp
to Vincent Snijders: You cannot use it like that. You would have to use an nested if then statement like: if…
Vincent Snijders wrote 38 lines
Terry Kemp schreef: > Hi All > > how do you do a case statement on a record of booleans e.g... > You cannot use it like that. You would have to use an nested if then statement like: if EngMode.ManualOp then ManualRun else if EngMode.ManualOp then LeakTest else etc. I would use an enum: type TEngMode = (emManualOp, emLeakTest, emDrainFlush); var EngMode : TEngMode; case EngMode of emManualOp: ManualRun; emLeakTest: LeakTestRun; emDrainFlush: DrainFlushTest; end; if several EngMode can occur at the same time (like can happen with EngModeRec) you can use type TEngModeSet = set of TEngMode; But then you cannot use case anymore to do the tests. HTH, Vincent

Hey! I like this enum method - the 'states' are to be mutually exclusive so this works great.

thanks alot