Re: AND statements

[philaldis(at)geocities.com (Phil Aldis)]

>>  If you write some code like this:
>> 
>>  test=Ptr_New()
>> 
>>  IF Ptr_Valid(test) AND Size(*test, /type) NE 10 THEN print, *test
>> 
>>  ....can you always guarantee that it will not try to evaluate the second
>>  statement if the first one was false - or is this a dangerous tactic to
>>  adopt?
>
>Nope. In fact, I can guarantee that it *will* evaluate the whole
>logical expression. IDL is in this respect totally unlike C.
>
>If the urge is big enough, one could ask RSI nicely to implement
>operators like "AND THEN" and "OR ELSE" used like this:
>
>   IF ptr_valid(test) AND THEN size(*test,/type) ne 10 then print,*test
>
>   IF error_occurred OR ELSE check_for_error() then print,"Error"
>
>"AND THEN" works like C &&
>"OR ELSE"  works like C ||, i.e. check_for_error() isn't called
>if "error_occurred" is already true. 
>

>Stein Vidar

So, to avoid that you have to do some pretty messy code. Say for
example I've got :

IF Ptr_Valid(ThisPointer) THEN BEGIN
	IF Size(*ThisPointer, /type) EQ 10 THEN BEGIN
			.
			.
			.
			.
			.
	ENDIF

ENDIF

However, I want to execute the same bit of code if it fails the
Ptr_Valid and the Size(*ThisPointer, type0 EQ 10, so as far as I can
see, (and I realise that I may be missing something pretty blatent),
you have to use flags

IF Ptr_Valid(ThisPointer) THEN BEGIN
	IF Size(*ThisPointer, /type) EQ 10 THEN BEGIN
			.
			.
			.
			.
			.
	ENDIF ELSE flag = 1

ENDIF ELSE flag = 1

IF flag ........

While obviously this is not the end of the world, there could be more
complex examples, and the code does look messy.

Cheers, 
Phil