Result variable multiple assignments in function

[FRex]

Is it okay to write to a Result variable in function multiple times? Will only the last write count as the return value from this function?

[wp]

Try this and see what happens:

Code: Pascal  [Select][+][-]

1. program Project1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. function Test: Integer;
6. begin
7.   Result := 1;
8.   Result := 2;
9.   Result := 3;
10. end;
11.  
12. begin
13.   WriteLn(Test());
14.  
15.   Readln;
16. end.

[Thaddy]

IOW yes, the last one is the final result. What that means, however, is that you can use result internally as a local variable to perform calculations inside a function.

Code: Pascal  [Select][+][-]

1. function UseResult(const s:string):string;
2. begin
3.   Result := s;  // use result as an internal local variable
4.   Result := Upcase(s);  //final result
5. end;

[FRex]

I know it works experimentally but my background is in C and C++ so I wanted to ask in case it's platform or options dependent feature like many in C and C++ often are.

[dbannon]

FRex, its widely done in lots of code that you will come across using Lazarus. I've seen it done in LCL and CCR components for example.

I've seen code where Result is passed to other methods to do what they will with it.

Its good, save a local variable in lots of cases.

Davo

[FRex]

I'm slowly relearning Pascal after 5 years of not using it at all and the last one I used was some old Delphi. I'm not reading LCL source code to learn.

[Thaddy]

I know it works experimentally but my background is in C and C++ so I wanted to ask in case it's platform or options dependent feature like many in C and C++ often are.

My example is not experimental at all but main stream in the FPC/Delphi Pascal world. It indeed saves a local variable and an assignment.
Some - like me - prefer it over a superfluous local. It is also fully cross-platform.
As far as the language dialect goes:
It needs {$mode objfpc} or {$mode Delpi} of {$mode Delphiunicode} It can be enabled in other supported dialects by {$modeswitch result} (Which is implied in the first three)

[FRex]

By experimental I meant trying out a piece of code to see what happens not if something is stable or not.

[Fungus]

No problem with that, I often use the result variable to do stuff in functions - like this:

Code: Pascal  [Select][+][-]

1. function FindString(const S: string; const List: TStrings): Integer;
2. begin
3.   for Result:= 0 to List.Count - 1 do if List[Result] = S then Exit;
4.   Result:= -1;
5. end;
6.  

[wildfire]

By experimental I meant trying out a piece of code...

In which case it's a simple experiment, why didn't you just try it?

Use a Black Box

[Thaddy]

When you are experimenting, also have a look at exit() which is an alternative way of returning from a function.
Slighty modified your own example for this:

Code: Pascal  [Select][+][-]

1. program Project1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. function Test: Integer;
6. begin
7.   Exit(1);
8.   Result := 2;
9.   Result := 3;
10. end;
11.  
12. begin
13.   WriteLn(Test());
14.   Readln;
15. end.

If you come from C(++) this may be more as you would expect. As you see Both can be combined..

[mangakissa]

This only works in an option range (I think) is set. Otherwise it results an error.

[Thaddy]

This only works in an option range (I think) is set. Otherwise it results an error.

No it works as expected. The result values with not be executed, the function exits immediately with the value 1..
I gave this example to experiment....
First compile and run before you shout error.... That's not true.

[Thaddy]

@Mangakissa here' a more useful example that also always works:

Code: Pascal  [Select][+][-]

1. function Test(const value:integer): Integer;
2. begin
3.   if value < 0 then exit(0);
4.   if value > 99 then exit(99);
5.   Result := value;
6. end;

No else needed. Compare to:

Code: Pascal  [Select][+][-]

1. function Test(const value:integer): Integer;
2. begin
3.   if value < 0 then result := 0 else
4.     if value > 99 then result :=99 else
5.       Result := value;
6. end;

Which is equivalent.

[molly]

Perhaps OP is more confident after reading the user manual on functions/result.

The only other thing that might perhaps be worth mentioning to a 'newbie' is that you can exit a function without providing a parameter to exit. That might work confusing if you aren't aware. e.g. you can mix result := x and make a call to exit; that way.