What is the proper approach to functions that have side-effects in Delphi/Pascal?

For example, I could have a boolean function DeleteFile that returns True if the file was deleted and False otherwise. How do I collect the return value?

1. The very explicit form would be:

   if DeleteFile(MyFilePath) then begin IsMyFileDeleted := True; end; else begin IsMyFileDeleted := False; end;

2. Less bulky would be:

   IsMyFileDeleted := False; if DeleteFile(MyFilePath) then begin IsMyFileDeleted := True; end;

3. Or even shorter, but discouraged by JEDI - perhaps it is acceptable just to collect return values:

   IsMyFileDeleted := False; if DeleteFile(MyFilePath) then IsMyFileDeleted := True;

My problem with 2 and 3 is that I explicitly state something (X := False) that I may not know for sure.

4. I would rather not set the variable beforehand and have its value completely determined by the function:

   IsMyFileDeleted := DeleteFile(MyFilePath);

Here the issue is that it is a bit misleading, because assigning a value to a boolean has a pretty serious side-effect. I'm not sure if this usage is desirable.

Some argue that functions should never have side-effects, but I think some of Pascals internal functions violate that.

5. The alternative would be making it procedures with a result variable to be filled by the procedure:

   DeleteFile(MyFilePath, IsMyFileDeleted);

That might go against the trend to keep parameter use to a minimum (Clean Code).

4 and 5 would be the only ways to collect a return value other than boolean, I suppose. Does that mean anything for boolean functions?

Yes, there are many ways to do the same thing, and maybe I'm just worried about nothing really, but I'm trying to develop a good style and I wonder if there are any best practices. For a beginner, many principles seem to be in conflict all the time.

What is the proper approach to functions that have side-effects in Delphi/Pascal?

For example, I could have a boolean function DeleteFile that returns True if the file was deleted and False otherwise. How do I collect the return value?

1. The very explicit form would be:

   if DeleteFile(MyFilePath) then begin IsMyFileDeleted := True; end; else begin IsMyFileDeleted := False; end;

2. Less bulky would be:

   IsMyFileDeleted := False; if DeleteFile(MyFilePath) then begin IsMyFileDeleted := True; end;

3. Or even shorter, but discouraged by JEDI - perhaps it is acceptable just to collect return values:

   IsMyFileDeleted := False; if DeleteFile(MyFilePath) then IsMyFileDeleted := True;

My problem with 2 and 3 is that I explicitly state something (X := False) that I may not know for sure.

4. I would rather not set the variable beforehand and have its value completely determined by the function:

   IsMyFileDeleted := DeleteFile(MyFilePath);

Here the issue is that it is a bit misleading, because assigning a value to a boolean has a pretty serious side-effect. I'm not sure if this usage is desirable.

Some argue that functions should never have side-effects, but I think some of Pascals internal functions violate that.

5. The alternative would be making it procedures with a result variable to be filled by the procedure:

   DeleteFile(MyFilePath, IsMyFileDeleted);

That might go against the trend to keep parameter use to a minimum (Clean Code).

4 and 5 would be the only ways to collect a return value other than boolean, I suppose? Does that mean anything for boolean functions?

Yes, there are many ways to do the same thing and maybe I'm just worried about nothing really, but I'm trying to develop a good style and I wonder if there are any best practices. For a beginner, many principles seem to be in conflict all the time.

What is the proper approach to functions that have side-effects in Delphi/Pascal?

For example, I could have a boolean function DeleteFile that returns True if the file was deleted and False otherwise. How do I collect the return value?

1. The very explicit form would be:

   if DeleteFile(MyFilePath) then begin IsMyFileDeleted := True; end; else begin IsMyFileDeleted := False; end;

2. Less bulky would be:

   IsMyFileDeleted := False; if DeleteFile(MyFilePath) then begin IsMyFileDeleted := True; end;

3. Or even shorter, but discouraged by JEDI - perhaps it is acceptable just to collect return values:

   IsMyFileDeleted := False; if DeleteFile(MyFilePath) then IsMyFileDeleted := True;

My problem with 2 and 3 is that I explicitly state something (X := False) that I may not know for sure.

4. I would rather not set the variable beforehand and have its value completely determined by the function:

   IsMyFileDeleted := DeleteFile(MyFilePath);

Here the issue is that it is a bit misleading, because assigning a value to a boolean has a pretty serious side-effect. I'm not sure if this usage is desirable.

Some argue that functions should never have side-effects, but I think some of Pascals internal functions violate that.

5. The alternative would be making it procedures with a result variable to be filled by the procedure:

   DeleteFile(MyFilePath, IsMyFileDeleted);

That might go against the trend to keep parameter use to a minimum (Clean Code).

Yes, there are many ways to do the same thing and maybe I'm just worried about nothing really, but I'm trying to develop a good style and I wonder if there are any best practices. For a beginner, many principles seem to be in conflict all the time.

What is the proper approach to functions that have side-effects in Delphi/Pascal?

For example, I could have a boolean function DeleteFile that returns True if the file was deleted and False otherwise. How do I collect the return value?

1. The very explicit form would be:

   if DeleteFile(MyFilePath) then begin IsMyFileDeleted := True; end; else begin IsMyFileDeleted := False; end;

2. Less bulky would be:

   IsMyFileDeleted := False; if DeleteFile(MyFilePath) then begin IsMyFileDeleted := True; end;

3. Or even shorter, but discouraged by JEDI - perhaps it is acceptable just to collect return values:

   IsMyFileDeleted := False; if DeleteFile(MyFilePath) then IsMyFileDeleted := True;

My problem with 2 and 3 is that I explicitly state something (X := False) that I may not know for sure.

4. I would rather not set the variable beforehand and have its value completely determined by the function:

   IsMyFileDeleted := DeleteFile(MyFilePath);

Here the issue is that it is a bit misleading, because assigning a value to a boolean has a pretty serious side-effect. I'm not sure if this usage is desirable.

Some argue that functions should never have side-effects, but I think some of Pascals internal functions violate that.

5. The alternative would be making it procedures with a result variable to be filled by the procedure:

   DeleteFile(MyFilePath, IsMyFileDeleted);

That might go against the trend to keep parameter use to a minimum (Clean Code).

4 and 5 would be the only ways to collect a return value other than boolean, I suppose. Does that mean anything for boolean functions?

Yes, there are many ways to do the same thing, and maybe I'm just worried about nothing really, but I'm trying to develop a good style and I wonder if there are any best practices. For a beginner, many principles seem to be in conflict all the time.