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dbosst
Apprentice
Joined: 15 Jun 2010
Posts: 121
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 Posted: Mon Aug 09, 2010 6:46 pm
3.22 %null
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I've used a mixture of %null(%1) and %1 == %null, and found today this problem:
This does not work fine:
#if (0 == %null) {#show {0 is null!}}
This works fine:
#if (%null(0)) {#show {0 is null!}}
the comparison of the integer 0 against %null fails in the first case |
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Tech
GURU
Joined: 18 Oct 2000
Posts: 2733
Location: Atlanta, USA
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Posted: Mon Aug 09, 2010 7:57 pm
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The first thing to realize is that the two statements are not the same.
%null is a predefined Variable that represents an empty variable value. %null() is a function that returns true if string is the null string. If string is left out then it returns a null string. That said there is a little something wonky, or at the very least counterintuitive, going on here.
Now consider the following:
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#if (0 == %null) {#show {0 is null!}} {#show {Oops I guess not}}
#if (%null(0)) {#show {0 is null!}} {#show {Zero and nothing are not equivalent}}
#if (%null("")) {#show {Nothing is nothing}} {#show {Err... nothing is something??}}
#if (%null()) {#show {Let's go here}} {#show {There is no there there}}
#if (%null == %null) {#show {0 is null! 2}} {#show {Oops I guess not 2}}
#if ("" == %null) {#show {0 is null! 3}} {#show {Oops I guess not 3}} |
In the second IF statement the argument to %null() is converted to a string, thus 0 becomes "0" which is of course not a null or empty string.
I would suggest you always use the function call unless you know you are always getting a string |
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Asati di tempari! |
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dbosst
Apprentice
Joined: 15 Jun 2010
Posts: 121
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Posted: Mon Aug 09, 2010 8:18 pm
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The problem I have is with the first case, though, I understand what you are saying.. my point is, if %null is representing an empty variable.. than comparing integer 0 to %null should always be false!
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Zugg
MASTER
Joined: 25 Sep 2000
Posts: 23379
Location: Colorado, USA
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Posted: Tue Aug 10, 2010 1:49 am
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%null() == 0 == FALSE == ""
so the first statement is correct. The above 4 items are equal because CMUD is a typeless language and is doing "autotype" stuff in the background.
As Tech mentioned, in the second case, %null takes a STRING argument, so %null(0) is the same as %null("0") and since "0" is NOT a null string, then it returns false.
So the second statement is also correct. |
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dbosst
Apprentice
Joined: 15 Jun 2010
Posts: 121
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Posted: Tue Aug 10, 2010 12:43 pm
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oh so %null() is interpreted to be equivalent to false (0) in a logical comparison, that's what was confusing me ... I thought %null() would be interpreted as actually nothing but not logically false, I guess I will stick to the second syntax then since this is a bit unusual to me
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Zugg
MASTER
Joined: 25 Sep 2000
Posts: 23379
Location: Colorado, USA
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Posted: Tue Aug 10, 2010 3:53 pm
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Yep, exactly. Because with *boolean* logic, all you have is True or False. "nothing" doesn't exist in boolean logic.
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