What exactly is the difference between the is_callable and function_exists in PHP?
Solution 1:
The function is_callable
accepts not only function names, but also other types of callbacks:
Foo::method
array("Foo", "method")
array($obj, "method")
- Closures and other invokable objects (PHP 5.3)
So is_callable
accepts anything that you could pass call_user_func
and family, while function_exists
only tells if a certain function exists (not methods, see method_exists
for that, nor closures).
Put another way, is_callable
is a wrapper for zend_is_callable
, which handles variables with the pseudo-type callback, while function_exists
only does a hash table lookup in the functions' table.
Solution 2:
When used with a function (not a class method) there is no difference except that function_exists
is slightly faster.
But when used to check the existence of methods in a class you cannot use function_exists
. You'll have to use is_callable
or method_exists
.
Solution 3:
When used in class context, is_callable
returns true for class methods that are accessible ie public methods but method_exists
returns true for all methods - public, protected and private. function_exists
does same thing as method_exists
outside class contexts.
Solution 4:
If a function Plop
exists then function_exists("Plop")
will return true.
See function_exists
If a variable is callable then is_callable($var)
will return true.
Now this could mean that $var
is a function name.
But i could also be an object and method name combo.
See is_callable