"0", as a string containing one character, is not something empty intuitively. Why does PHP treat it as FALSE when converted to a boolean, unlike other programming languages?
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PHP was designed (or, rather, evolved) for use with web requests, where you're frequently dealing with string input (URL parameters, or POST requests from a form in a browser). As such, it will automatically cast strings to other types.
A simple example of this is that '1' + '2' gives 3, not an error, or '12', or some other interpretation. By the same logic, the string '0' can be used as a numeric 0.
Meanwhile, like many languages, PHP treats certain values as "falsy" when cast to boolean - things that are intuitively "empty", as you say. That includes numeric 0, as well as the empty string '' and the empty array []. In an if statement, the expression is explicitly cast to boolean, so if ( 0 ) is the same as if ( false ).
Putting these two things together, you get a conundrum: on the one hand, as you say '0' is a non-empty string; on the other hand, we have said that it can be used as a numeric 0, which is "empty". PHP opts to treat the "zero-ness" as more important than the "stringiness", so that '0' is considered "falsy".
In short: '0' == 0 == false; or (bool)'0' === (bool)(int)'0'
IMSoP
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According to the PHP documentation on booleans, it says that:
When converting to boolean, the following values are considered
FALSE
...
the empty string, and the string "0"
...
Otherwise:
Every other value is considered TRUE (including any resource).
If you run:
var_dump((bool) "0");
It will print:
bool(false)
So it's working as expected.
To explicitly answer your question:
However, in most cases the cast is unnecessary, since a value will be automatically converted if an operator, function or control structure requires a boolean argument.
This means that PHP's "autocast" will cast "0" to integer 0, which is FALSE as well in a control structure like say an if() statement.
kayess
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