Actually, it can be easily done as a 2 step operation with the use of a
lookup table of addresses.
0: address of (0)
1: "
2: "
3: "
4: address if (2)
etc.
Then do Jump (lookup(foo)). You get the picture.
However, the limitations of this and other switch statement comes when you
add a new case to your business requirements. *Chances* are you will need
to fix up lots of switch statements and lookup tables. With OO you
add/register another class to your factory ... trivial.
Dennis.
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On
> Behalf Of Matt Powell
> Sent: Wednesday, 16 February 2000 10:39
> To: Multiple recipients of list delphi
> Subject: Re: [DUG]: VB Like Case statement
>
>
> > In theory OO programming never needs a switch statement.
>
> No, but it can be written and compiled a lot more efficiently using a
> switch statement. It need not take O(n/2) comparisons to
> switch, either.
> It is possible to take O(log n) comparisons:
>
> case foo of
> 0..3: blarg(1);
> 4, 11: blarg(2);
> 5: blarg(3);
> 6-8: blarg(4);
> 9: blarg(5);
> 10: blarg(6);
> end;
>
> ...can be compiled as:
>
> if foo >= 6 then goto 9;
> 0:
> if foo > 3 then goto 4;
> blarg(1);
> 4:
> if foo = 5 then goto 5;
> blarg(2);
> goto end;
> 5:
> blarg(3);
> goto end;
> 6:
> blarg(4);
> goto end;
> 9:
> if foo < 9 then goto 6;
> if foo >= 10 then goto 10;
> blarg(5);
> goto end;
> 10:
> if blarg = 11 then goto 4;
> blarg(6);
> end:
>
> ...effectively performing a binary search for the number you want.
>
> This sort of binary-select is not difficult to do automatically - you
> just have to look out for multiple disjoint ranges (like 4,11) that
> share blocks of code. Does anyone know if any compilers actually
> implement this method?
>
> - Matt
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