Pros and Cons of using SWITCH

[Atrix]

Hi,I was just wondering if there were any cons to using the Switch function over if..elseif.. statements.I know the pro of switch is so that you dont have to have long lines of if...elseif.. statements, but no tutorial tells you if there are any cons to using switch over if..elseifs..or when the best time to use if...elseif and switch.I just want to learn the best practices of when you should use switch and when you shouldn't. That's if there any cons, there might not be and it might be just what ever it suits the coder.

[Synook]

If you have complex conditions, you probably won't be able to express them efficiently in a switch statement.

[Atrix]

and what would be classed as a complex condition?

[jeffman]

If you need to test more than one value, for example. Likeif ( (isset($_POST['user']) && $age > 37) || $pizza == 'cheese' )hard to handle that with a switch.As far as I'm concerned, switch is mostly syntactic candy for the programmer -- a way of avoiding the difficulty of reading multiple if-else blocks. As soon as you start nesting if-blocks in a case statement, all that disappears.FWIW, you see no significant performance differences until you hit thousands of iterations. IMO: unless you're really HAMMERING on a database, use the structure that works best and looks easiest to read and maintain.

[Synook]

Also if you need to test more than one condition for a variable:

if ($a > 5 && $a < 20)

Basically, any condition involving a logical operator.

[Atrix]

FWIW, you see no significant performance differences until you hit thousands of iterations. IMO: unless you're really HAMMERING on a database, use the structure that works best and looks easiest to read and maintain.

When you say that. Do you mean if your hammering the database if..elseif statements slow it down and switch would be quicker or the other way around?Just want to make sure I understand the effect it has.

[Synook]

Switches are faster than if statements.

[justsomeguy]

Do you mean if your hammering the database if..elseif statements slow it down

No, hammering the database is going to slow it down, not a PHP control structure.

Just want to make sure I understand the effect it has.

Test it out. You can set up a loop to run a piece of code several thousand times and use microtime to keep track with how long it took.

Basically, any condition involving a logical operator.

Not necessarily:

switch (true){  case $a < $b:  break;  case $b < $c:  break;    case $c < $d:  break;}

And if you think that looks weird, you'll love Duff's Device:

send(to, from, count)register short *to, *from;register count;{	register n=(count+7)/8;	switch(count%8){	case 0:	do{	*to = *from++;	case 7:		*to = *from++;	case 6:		*to = *from++;	case 5:		*to = *from++;	case 4:		*to = *from++;	case 3:		*to = *from++;	case 2:		*to = *from++;	case 1:		*to = *from++;		}while(--n>0);	}}

Yeah, he interleaved a switch and a loop.

[ShadowMage]

Not necessarily:

switch (true) {  case $a < $b:	break;  case $b < $c:	break;  case $c < $d:	break;}

So that's how that's done! I always wondered if that was possible with PHP. I've tried to do it but I could never get it to work.

And if you think that looks weird, you'll love Duff's Device:

send(to, from, count)register short *to, *from;register count;{	register n=(count+7)/8;	switch(count%8){	case 0:	do{	*to = *from++;	case 7:		*to = *from++;	case 6:		*to = *from++;	case 5:		*to = *from++;	case 4:		*to = *from++;	case 3:		*to = *from++;	case 2:		*to = *from++;	case 1:		*to = *from++;		}while(--n>0);	}}

Yeah, he interleaved a switch and a loop.

That's insane.

[Synook]

Not necessarily:

Well, when I said logical operators I meant only &&, ||, !, etc, and not comparison operators.

[justsomeguy]

The operators don't matter, just the values the expressions evaluate to. A switch statement is just a series of expressions which all get compared to a certain value, and the first one which matches gets executed.

switch (true){  case $a || $b:  break;    case $c || $d:  break;    case $e && $f:  break;  case !$g:  break;}

[chibineku]

Reading about Duff's Device, someone said that it functions incorrectly in the event of len/8 having no modulus, which I thought myself from reading it. But, it doesn't - if there's no remainder, then length is exactly 8, so you need to do the operation completely. If there is a remainder, then you need to deal with the remainder first, right? It's one of those bits of code that looks like magic and, at least for me, requires some serious thought. I'm glad that I don't have to deal with memory allocation

[justsomeguy]

It assumes that count is a positive integer, which is a safe assumption to make since in that case it will be a register address and you don't have registers with negative or fractional addresses.