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Wildhoney · 06-22-2008, 02:44 PM

Each of these require a little more than one line to adequately explain, so I will cherry pick #4.

As you know, a conditional statement, such as the if block, will only be entered if the value is true. So by prepending an exclamation mark to a variable, you are inverting its value. However, many values cannot be successfully inverted. A string, for instance, cannot be inverted -- only reversed. To an invert a word, I would assume, you would have to find its antonym. In computer languages, such as PHP, this does not apply, as everything is reduced to either true or false, 1 or 0, yes or no.

Thus, if I inverted a string it would naturally be inverted to false. Conversely, if I were to invert a false value, it would become true. Therefore once you place that in a conditional if statement, any variable that is true, will become false, and thus not enter that if statement.

For instance:

php Code:

$bValue = 'TalkPHP.com';

if (!$bValue)
{
    die('Variable was inverted to true');
}

die('Variable was inverted to false');

To enter the if statement block, the initial value would have had to have been false to begin with, or any value which denotes a false value -- such as null.

Why did I write all that? Well, I personally think that's the best way to understand your #4 question. Both are somewhat similar, but in the first example you're inverting the value, and in the second you're merely looking for a non-matching value. Both, insofar as I can see, will produce the same results, but the latter should be used, at least in my opinion, in such an instance. I reserve the inverting of values for if statements, as seen above.

In addendum, you can invert values as much as you like. Consider the following:

php Code:

$bValue = false;
var_dump(!!!$bValue);

Inverted the variable 3 times, from its initial state of false:

True
False
True (Final state)

I hope this answers your question thoroughly!

06-22-2008, 02:44 PM	#2 (permalink)
Wildhoney La Vida es Sueño Join Date: Sep 2007 Location: Oldham Posts: 2,280 Thanks: 90	Each of these require a little more than one line to adequately explain, so I will cherry pick #4. As you know, a conditional statement, such as the `if` block, will only be entered if the value is `true`. So by prepending an exclamation mark to a variable, you are inverting its value. However, many values cannot be successfully inverted. A string, for instance, cannot be inverted -- only reversed. To an invert a word, I would assume, you would have to find its antonym. In computer languages, such as PHP, this does not apply, as everything is reduced to either `true` or `false`, 1 or 0, yes or no. Thus, if I inverted a string it would naturally be inverted to `false`. Conversely, if I were to invert a `false` value, it would become `true`. Therefore once you place that in a conditional `if` statement, any variable that is `true`, will become `false`, and thus not enter that `if` statement. For instance: php Code: $bValue = 'TalkPHP.com'; if (!$bValue) { die('Variable was inverted to true'); } die('Variable was inverted to false'); To enter the `if` statement block, the initial value would have had to have been `false` to begin with, or any value which denotes a `false` value -- such as `null`. Why did I write all that? Well, I personally think that's the best way to understand your #4 question. Both are somewhat similar, but in the first example you're inverting the value, and in the second you're merely looking for a non-matching value. Both, insofar as I can see, will produce the same results, but the latter should be used, at least in my opinion, in such an instance. I reserve the inverting of values for `if` statements, as seen above. In addendum, you can invert values as much as you like. Consider the following: php Code: $bValue = false; var_dump(!!!$bValue); Inverted the variable 3 times, from its initial state of `false`: True False True (Final state) I hope this answers your question thoroughly! __________________ The man who comes back through the Door in the Wall will never be quite the same as the man who went out.