lazarus have if_variant. how to improve for fpc? [SOLVED]

[d2010]

Hello  I discovery in Delphi3Old the function if_variant
The function "if_variant" contatin too many bugs in Delphi3.
--a) how to compare s1,s2 with nil value OR how to protect  if_variant with Nil crash

Code: [Select]

Function if_variant(condtion:wordbool;s1,s2:variant):variant;
Begin 
       if (condtion) then if_variant:=s1 else    if_variant:=s2;
End;


[Lansdowne]

While requires a Boolean, so surely you don't need to use any Variant there?

As far as I know, if a or b will not try to evaluate b if a is True. So depending on what you're trying to do, would this work?

Replace
 

Code: Pascal  [Select][+][-]

1. while (if_variant(extmax<>nil,(extmin<extmax)and(extmin^<>atonexit_c),extmin^<>atonexit_c)) do
2.  

with
 

Code: Pascal  [Select][+][-]

1. while (extmin^<>atonexit_c) and ((extmax=nil)or(extmin<extmax)) do
2.  

[Fibonacci]

There is generic IfThen in SysUtils.

In your case you can use it like this:

Code: Pascal  [Select][+][-]

1. while specialize IfThen<Boolean>(extmax <> nil, (extmin < extmax) and (extmin^ <> atonexit_c), extmin^ <> atonexit_c) do begin
2.   // ...
3. end;

If you want Variant version, thats possible too:

Code: Pascal  [Select][+][-]

1. writeln('true  = ', specialize IfThen<Variant>(true,  42, 'hello'));
2. writeln('false = ', specialize IfThen<Variant>(false, 42, 'hello'));

[Lansdowne]

Whatever you write in ???? and ??? should include setting result:=.

Beyond that, all I suggest is not to use Variant unless you genuinely need it.

Or if, as a beginner to Pascal, you want to explore how pointers work, do some simple test routines to make sure understand how they work with the usual Types such as String, PChar, Integer (perhaps including ShortInt and Smallint).  And I wouldn't use Cardinal, as far as I know that is rarely used.

[Thaddy]

The second part of Fibonacci's last answer is what you want. Try that first. (I wrote the generic ifthen from sysutils)

[d2010]

Whatever you write in ???? and ??? should include setting result:=.
Beyond that, all I suggest is not to use Variant unless you genuinely need it.
Or if, as a beginner to Pascal, you want to explore how pointers work, do some simple test routines to make sure understand how they work with the usual Types such as String, PChar, Integer (perhaps including ShortInt and Smallint).  And I wouldn't use Cardinal, as far as I know that is rarely used.

Thank you guy. God bless you.
Thank you guy. God bless you.
==I need only try except inside/outside for  if_variant source code, and  forced all if_variant/s to
_inline or _assembler. Many bugs inside Delphi7 , are cannot force to __inline; even
in Lazarus.fpc.exe.
or otherwise you can
  ifhen (test:boolean; ti,tf:integer):integer;??? inline
  ifthen(test:boolean; Const st,sf:string):string;??? inline
  ifthen (test:boolean; di,df:double):double; ??? inline
Best Regards

[Thaddy]

You really need only

Code: Pascal  [Select][+][-]

1. {$mode objfpc}
2. writeln('true  = ', specialize IfThen<Variant>(true,  42, 'hello'));
3. writeln('false = ', specialize IfThen<Variant>(false, 42, 'hello'));

or

Code: Pascal  [Select][+][-]

1. {$mode delphi}
2. writeln('true  = ', IfThen<Variant>(true,  42, 'hello'));
3. writeln('false = ', IfThen<Variant>(false, 42, 'hello'));

[d2010]

Thank/s

[d2010]

You really need only

Code: Pascal  [Select][+][-]

1. {$mode objfpc}
2. writeln('true  = ', specialize IfThen<Variant>(true,  42, 'hello'));
3. writeln('false = ', specialize IfThen<Variant>(false, 42, 'hello'));

or

Code: Pascal  [Select][+][-]

1. {$mode delphi}
2. writeln('true  = ', IfThen<Variant>(true,  42, 'hello'));
3. writeln('false = ', IfThen<Variant>(false, 42, 'hello'));

\

Thank you , that is solution.