On 17 November 2006 09:55, Michael wrote:
> This will be my last post on this thread of discussion.
>
> Thanks to all who replied, I have it figured out.
>
> I guess my only problem with the way the !== and ===
> operators work in this situation is this:
>
> Logic dictates that if something evaluates to NOT FALSE it
> must be TRUE.
Um, yes, but it's the *test* that's evaluating to NOT FALSE (and obeys this rule), which says nothing about the actual values involved in the test. Even with the != operator you can demonstrate this point:
$x = "yes";
if ($x!=FALSE) { echo "\$x must be TRUE" }
will display the message, even though $x contains the string "yes" (because the string "yes" in a Boolean context evaluates to TRUE).
> if !== evaluates to TRUE then === should also under the same
> conditions (all other things being equal)
I don't think that's quite what you meant, but I think I understand the point you were getting at, and it's not valid. If something !==FALSE, then TRUE is one of the values it may be === to -- but so are all the integers, all the floating numbers, all the strings, all possible objects, ....
In other words, if $x!==FALSE, it *might* be ===TRUE, but it *might* also be ===0, ===1, ===1.0 (not the same as 1!), ==="hello world", etc.
The *test* *itself*, however, would obey that rule -- that the *test* returns a Boolean value says nothing about the types of its operands.
> if !== evaluates an integer 0 to TRUE, so should ===
Neither of them can evaluate an integer 0 to TRUE, as 0 and TRUE are different types. You're confusing how these operators evaluate their operands with the resulting value of the test: the === and !== operators will both evaluate an integer 0 as 0 -- it's the result of the test that will be strictly either TRUE or FALSE. (As it happens, 0 and FALSE also give different values when evaluated by ==/!=, so you'd have the same conceptual problem with those operators).
> , it
> can't be true and still return a false value. The !== and ===
> operators work differently, they should be complimentary.
No, they work exactly the same. Both of them *first* look at the types of the two values, and *if and only if* the types are the same are the values compared.
So: 0!==FALSE will succeed immediately, returning TRUE, because the types differ
and: 0===FALSE will fail immediately, returning FALSE, because the types differ
which are as you expected the complementary Boolean values.
*However*:
1!==FALSE returns TRUE by the same logic, and
1===TRUE returns the complementary FALSE
Immediately, then, you can see that we have two values that are both !==FALSE, and yet neither of them is the value TRUE.
I'm afraid I've gone on at some length here, but I felt throughout this thread that you really hadn't grasped the underlying conceptual point, and I hope some of my examples may have helped illuminate it for you.
Cheers!
Mike
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