Page 74 - Beginning PHP 5.3

Part II: Learning the Language
As well as the four scalar types, PHP supports two compound types. Compound data is data that can
contain more than one value. The following table describes PHP ’ s compound types:

Compound Data Type Description
Array An ordered map (contains names or numbers mapped to values)

Object A type that may contain properties and methods

You look at arrays in Chapter 6 , and objects in Chapter 8 .

Finally, PHP supports two special data types, so called because they don ’ t contain scalar or compound
data as such, but have a specific meaning:

Special Data Type Description
Resource Contains a reference to an external resource, such as a file or database

Null May only contain null as a value, meaning the variable explicitly
does not contain any value

About Loose Typing

PHP is known as a loosely - typed language. This means that it ’ s not particularly fussy about the type of
data stored in a variable. It converts a variable ’ s data type automatically, depending on the context in
which the variable is used. For example, you can initialize a variable with an integer value; add a float
value to it, thereby turning it into a float; then join it onto a string value to produce a longer string.
In contrast, many other languages, such as Java, are strongly - typed ; once you set the type of a variable in
Java, it must always contain data of that type.

PHP ’ s loose typing is both good and bad. On the plus side, it makes variables very flexible; the same
variable can easily be used in different situations. It also means that you don ’ t need to worry about
specifying the type of a variable when you declare it. However, PHP won ’ t tell you if you accidentally
pass around data of the wrong type. For example, PHP will happily let you pass a floating - point value to
a piece of code that expects to be working on an integer value. You probably won ’ t see an error
message, but you may discover that the output of your script isn ’ t quite what you expected! These types
of errors can be hard to track down. (Fortunately, there is a way to test the type of a variable, as you see
in a moment.)

Testing the Type of a Variable
You can determine the type of a variable at any time by using PHP ’ s gettype() function. To use
gettype() , pass in the variable whose type you want to test. The function then returns the variable ’ s
type as a string.

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