PHP Types

Four scalar types:

boolean (expresses a truth value. It can be either TRUE or FALSE.)

integer (is a number of the set Z = {..., -2, -1, 0, 1, 2, ...}. )

float (floating-point number, aka 'double', like $a = 1.234;)

string (is series of characters)

Two compound types:

array

array is actually an ordered map. This type is optimized in several ways, so you can use it as a real array, or a list (vector), hashtable (which is an implementation of a map), dictionary, collection, stack, queue and probably more. Because you can have another PHP array as a value, you can also quite easily simulate trees.

An array can be created by the array() language-construct. It takes a certain number of comma-separated key => value pairs.

<?php
$arr = array("foo" => "bar", 12 => true);

echo $arr["foo"]; // bar
echo $arr[12]; // 1
?>

A key may be either an integer or a string.

object

To initialize an object, you use the new statement to instantiate the object to a variable.

<?php
class foo
{
function do_foo()
{
echo "Doing foo.";
}
}
$bar = new foo;
$bar->do_foo();
?>

two special types:

resource

A resource is a special variable, holding a reference to an external resource. Resources are created and used by special functions

NULL

NULL is the only possible value of type NULL. Used like $abc=null

some pseudo-types:

mixed

mixed indicates that a parameter may accept multiple (but not necessarily all) types.

number

number indicates that a parameter can be either integer or float.

callback

Callback functions can not only be simple functions but also object methods including static class methods.