PHP - extract() type
Question
PHP's extract()
function can take on one of several extract_types
. But what's the difference between extr_prefix_same
and extr_prefix_if_exists
? The manual makes it sound like, in either case, new variables will be prefixed if the variable name already exists.
Thanks!
Solution
When using EXTR_PREFIX_IF_EXISTS
, if the variable doesn't already exist then the prefixed version won't be created either. In this example:
function test() {
$a = 12345;
extract(array('a' => 1, 'b' => 2, 'c' => 3), EXTR_PREFIX_IF_EXISTS, 'my_');
var_export(get_defined_vars());
}
test();
$my_b
and $my_c
aren't created because $b
and $c
don't exist.
OTHER TIPS
EXTR_PREFIX_SAME
will extract all variables, and only prefix ones that exist in the current scope.
EXTR_PREFIX_IF_EXISTS
will only extract variables that exist in the current scope, and prefix them with the desired prefix.
So, for example:
$foo = 'foo';
$bar = 'bar';
extract(array('foo' => 'moo', 'bar' => 'mar', 'baz' => 'maz'), EXTR_PREFIX_IF_EXISTS, 'prefix');
isset($prefix_foo); // true
isset($prefix_baz); // false
isset($baz); // false
While....
$foo = 'foo';
$bar = 'bar';
extract(array('foo' => 'moo', 'bar' => 'mar', 'baz' => 'maz'), EXTR_PREFIX_SAME, 'prefix');
isset($prefix_foo); // true
isset($prefix_baz); // false
isset($baz); // true
Based on the manual definitions, EXTR_PREFIX_SAME
will create variables based on the key name, and if a variable in the local space already exists, a prefix will be added to the variable name.
By contrast, EXTR_PREFIX_IF_EXISTS
would appear to inherit the behavior of EXTR_IF_EXISTS
(only overwrite if the variables already exist), but instead of overwriting the local variables, a prefixed version will be created.
Consider the following
$array = Array();
$array['foo'] = 'foo';
$array['bar'] = 'bar';
$array['baz'] = 'baz';
$foo = 'local foo';
$bar = 'local bar';
extract($array, EXTR_PREFIX_SAME, 'pre');
print_r(get_defined_vars());
//partial output
//Array
//(
// [array] => Array
// (
// [foo] => foo
// [bar] => bar
// [baz] => baz
// )
//
// [foo] => local foo
// [bar] => local bar
// [pre_foo] => foo
// [pre_bar] => bar
// [baz] => baz
//)
So with EXTR_PREFIX_SAME
, the values of $foo and $bar will remain the same, and three new local variables ($pre_foo, $pre_bar, and $baz) will be defined. However if we use EXTR_PREFIX_IF_EXISTS
$array = Array();
$array['foo'] = 'foo';
$array['bar'] = 'bar';
$array['baz'] = 'baz';
$foo = 'local foo';
$bar = 'local bar';
extract($array, EXTR_PREFIX_IF_EXISTS, 'pre');
print_r(get_defined_vars());
//partial output
//Array
//(
// [array] => Array
// (
// [foo] => foo
// [bar] => bar
// [baz] => baz
// )
//
// [foo] => local foo
// [bar] => local bar
// [pre_foo] => foo
// [pre_bar] => bar
//)
The values of $foo and $bar are still preserved, but only TWO new variables are imported into the local space. Since $baz isn't a variable that already exists the EXTR_PREFIX_IF_EXISTS
tells PHP to ignore the 'baz' key in the array.