对于PHP4

…这转载的错误：

$foo = 'bar';

$foo[0] = 'bar';

对于PHP5

…这转载的错误：

$foo = 'bar';

if (is_array($foo['bar']))

echo 'bar-array';

if (is_array($foo['bar']['foo']))

echo 'bar-foo-array';

if (is_array($foo['bar']['foo']['bar']))

echo 'bar-foo-bar-array';

编辑，

so why doesn’t the error appear in the

first if condition even though it is a

string.

因为PHP是一个非常宽容的编程语言，我猜。我将用代码来说明我的想法：

$foo = 'bar';

// $foo is now equal to "bar"

$foo['bar'] = 'foo';

// $foo['bar'] doesn't exists - use first index instead (0)

// $foo['bar'] is equal to using $foo[0]

// $foo['bar'] points to a character so the string "foo" won't fit

// $foo['bar'] will instead be set to the first index

// of the string/array "foo", i.e 'f'

echo $foo['bar'];

// output will be "f"

echo $foo;

// output will be "far"

echo $foo['bar']['bar'];

// $foo['bar'][0] is equal calling to $foo['bar']['bar']

// $foo['bar'] points to a character

// characters can not be represented as an array,

// so we cannot reach anything at position 0 of a character

// --> fatal error