rfc:consistent_callables
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rfc:consistent_callables [2017/05/28 01:28] – danack | rfc:consistent_callables [2019/04/28 02:58] – danack | ||
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====== PHP RFC: Consistent Callables ====== | ====== PHP RFC: Consistent Callables ====== | ||
- | * Version: 0.9 | + | * Version: 0.95 |
- | * Date: 2015-09-28 | + | * Date: 2019-04-28 |
* Author: Dan Ackroyd | * Author: Dan Ackroyd | ||
- | * Status: | + | * Status: |
* First Published at: https:// | * First Published at: https:// | ||
Line 13: | Line 13: | ||
The two aims of this RFC are: | The two aims of this RFC are: | ||
- | + | ||
- | i) to make callable be a consistent type, so that it can be used safely without regard to the location where it is being used. | + | i) to make 'callable' |
ii) Make call_user_func be equivalent to calling a callable through direct invocation. i.e. for a callable that requires zero arguments, if the code `call_user_func($callable); | ii) Make call_user_func be equivalent to calling a callable through direct invocation. i.e. for a callable that requires zero arguments, if the code `call_user_func($callable); | ||
+ | |||
+ | ==== Summary of changes, aka tl:dr version ==== | ||
+ | |||
+ | 1) Modify the callable type check for parameter and return types, so that only values that are universally callable pass the type check. | ||
+ | |||
+ | 2) Add function is_callable_type(mixed $var) : bool - returns true if the parameter can be passed as a callable type, and is callable in any scope, otherwise returns false. | ||
+ | |||
+ | 3) Modify the current is_callable() function to only return true for values that will be callable in the current scope. | ||
+ | |||
+ | 4) self, parent and other non-resolved strings will no longer be usable either in string or array based callables i.e. neither ' | ||
==== Example problems ==== | ==== Example problems ==== | ||
This section lists the problems with the current implementation of callables. I believe it is complete, though it may not be due to the magic of re-binding methods. | This section lists the problems with the current implementation of callables. I believe it is complete, though it may not be due to the magic of re-binding methods. | ||
- | |||
=== Callable type is inconsistent === | === Callable type is inconsistent === | ||
Line 32: | Line 41: | ||
echo " | echo " | ||
} | } | ||
+ | |||
class Bar { | class Bar { | ||
private static function staticMethod() { | private static function staticMethod() { | ||
} | } | ||
+ | |||
public function testMethod(callable $callable) { | public function testMethod(callable $callable) { | ||
echo " | echo " | ||
Line 42: | Line 51: | ||
} | } | ||
} | } | ||
+ | |||
$callable = [' | $callable = [' | ||
+ | |||
$obj = new Bar(); | $obj = new Bar(); | ||
$obj-> | $obj-> | ||
- | + | ||
+ | |||
// output is | // output is | ||
// testInClass OK | // testInClass OK | ||
// Fatal error: Argument 1 passed to testFunction() must be callable, array given, called in | // Fatal error: Argument 1 passed to testFunction() must be callable, array given, called in | ||
// %d on line %d and defined in %s on line %d | // %d on line %d and defined in %s on line %d | ||
+ | |||
</ | </ | ||
i.e. even though the parameter was a valid callable type when passed to the instance method of the class, it became an invalid callable when passed to the function. | i.e. even though the parameter was a valid callable type when passed to the instance method of the class, it became an invalid callable when passed to the function. | ||
- | === Private / protected methods report as callable when they are not === | + | === Private / protected methods report as callable when they are not === |
<code php> | <code php> | ||
- | |||
class A | class A | ||
{ | { | ||
Line 66: | Line 74: | ||
return is_callable($param); | return is_callable($param); | ||
} | } | ||
- | | + | |
private function privateMethod() { | private function privateMethod() { | ||
echo "This is a private method"; | echo "This is a private method"; | ||
} | } | ||
+ | |||
public function test($param) { | public function test($param) { | ||
if ($this-> | if ($this-> | ||
Line 77: | Line 85: | ||
} | } | ||
} | } | ||
+ | |||
class B extends A | class B extends A | ||
{ | { | ||
Line 86: | Line 94: | ||
} | } | ||
} | } | ||
+ | |||
$a = new A(); | $a = new A(); | ||
$b = new B(); | $b = new B(); | ||
+ | |||
$callable = [$a, ' | $callable = [$a, ' | ||
+ | |||
$a-> | $a-> | ||
$b-> | $b-> | ||
+ | |||
// Output is | // Output is | ||
// This is a private method | // This is a private method | ||
Line 101: | Line 109: | ||
</ | </ | ||
- | i.e. despite checking with `is_callable` if something is callable, the program crashes because `is_callable` lied to us. | + | i.e. despite checking with `is_callable` if something is callable, the program crashes because `is_callable` lied to us. |
- | === Instance method reported as callable === | + | === Instance method reported as callable === |
- | The is_callable function reports an instance method as callable on a class. It should not callable and that behaviour is already deprecated. Instance methods should only callable on instances. | + | The is_callable function reports an instance method as callable on a class. It should not be callable and that behaviour is already deprecated. Instance methods should only callable on instances. |
<code php> | <code php> | ||
+ | |||
class Foo { | class Foo { | ||
function bar() { | function bar() { | ||
Line 113: | Line 122: | ||
} | } | ||
} | } | ||
+ | |||
$callable = [' | $callable = [' | ||
var_dump(is_callable($callable)); | var_dump(is_callable($callable)); | ||
$callable(); | $callable(); | ||
- | + | ||
+ | |||
//Output is: | //Output is: | ||
// | // | ||
Line 125: | Line 134: | ||
</ | </ | ||
- | === The method invoked varies depending where the callable is called from === | + | === The method invoked varies depending where the callable is called from === |
For callables that use `self` or `parent` as part of the definition of the callable, the actual code that will be invoked varies depending on where the callable was called from. | For callables that use `self` or `parent` as part of the definition of the callable, the actual code that will be invoked varies depending on where the callable was called from. | ||
<code php> | <code php> | ||
+ | |||
class Foo { | class Foo { | ||
public static function getCallable() { | public static function getCallable() { | ||
Line 141: | Line 151: | ||
} | } | ||
} | } | ||
+ | |||
class Bar { | class Bar { | ||
public function process(callable $callable) { | public function process(callable $callable) { | ||
Line 149: | Line 159: | ||
echo "This is bar:: | echo "This is bar:: | ||
} | } | ||
- | | + | |
public static function getCallable() { | public static function getCallable() { | ||
return ' | return ' | ||
} | } | ||
} | } | ||
+ | |||
$foo = new Foo(); | $foo = new Foo(); | ||
$bar = new Bar(); | $bar = new Bar(); | ||
$callable = $foo-> | $callable = $foo-> | ||
$bar-> | $bar-> | ||
+ | |||
$callable = $bar-> | $callable = $bar-> | ||
$foo-> | $foo-> | ||
- | + | ||
+ | |||
// Output is: | // Output is: | ||
// This is bar::hello | // This is bar::hello | ||
Line 173: | Line 183: | ||
i.e. calling `self:: | i.e. calling `self:: | ||
- | + | === call_user_func different from is_callable === | |
- | + | ||
- | === call_user_func different from is_callable === | + | |
In this example the result of calling something through call_user_func and invoking it directly is different. | In this example the result of calling something through call_user_func and invoking it directly is different. | ||
<code php> | <code php> | ||
+ | |||
class foo { | class foo { | ||
public static function getCallable() { | public static function getCallable() { | ||
Line 197: | Line 206: | ||
$callable = $foo-> | $callable = $foo-> | ||
$foo-> | $foo-> | ||
+ | |||
$bar-> | $bar-> | ||
+ | |||
// Output is: | // Output is: | ||
// This is foo::bar | // This is foo::bar | ||
Line 211: | Line 220: | ||
===== Details of changes ===== | ===== Details of changes ===== | ||
- | ==== Definition of valid values for callable type ==== | + | ==== Definition of valid values for callable type ==== |
The following would be the complete list of valid values for the callable type: | The following would be the complete list of valid values for the callable type: | ||
- A string that is the name of a function. | - A string that is the name of a function. | ||
- | - An array consisting of two elements; a string at index 0 which is a valid class name, and a string at index 1 which must meet the conditions: | + | - An array consisting of two elements; a string at index 0 which is a valid fully qualified |
- | * either be the name of a public static function of the class or the class must have a magic %%__callStatic%% method. | + | * either be the name of a public static function of the class or the class must have a magic __callStatic method. |
- | * the name must not be that of an instance method. | + | |
- | - An array consisting of two elements; an object at index 0, and a string at index 1 where either the string is the name of a public method of the object, or the object has a magic %%__call%% method. | + | |
+ | - An array consisting of two elements; an object at index 0, and a string at index 1 where either the string is the name of a public method of the object, or the object has a magic __call method. | ||
- An instance of a class (an object) where the class has a public __invoke() method. | - An instance of a class (an object) where the class has a public __invoke() method. | ||
- Closures, which includes anonymous functions. | - Closures, which includes anonymous functions. | ||
- | + | Note - Does not affect calling private/ | |
- | ==== Note - removal of colon separated string ==== | + | |
- | + | ||
- | This removes the ability to define a callable as a single string composing a class-name and a method name separated by double-colons. The reasons for this are that: | + | |
- | + | ||
- | * It is duplication of ii. The duplication of code is not just in PHP core, but for all userland code and libraries that analyze callables must duplicate the handling. | + | |
- | + | ||
- | * For things like routing libraries it is useful for users to be able to specify not a valid callable, but instead a class that needs to be instantiated and the method that should be called on the instantiated object. Having ' | + | |
- | + | ||
- | * It was introduced without much discussion to address a problem in the SPL iterator. | + | |
- | https:// | + | |
- | + | ||
- | * It is easier (in the sense of fewer CPU operations) to validate [' | + | |
- | + | ||
- | + | ||
- | ==== Note - Does not affect calling private/ | + | |
While they would no longer pass the type checker for the callable type, private and protected methods could still be executed through call_user_func and direct invocation. | While they would no longer pass the type checker for the callable type, private and protected methods could still be executed through call_user_func and direct invocation. | ||
Line 245: | Line 240: | ||
class Foo { | class Foo { | ||
private function bar() { } | private function bar() { } | ||
- | | + | |
private function getCallback() { | private function getCallback() { | ||
return [$this, ' | return [$this, ' | ||
} | } | ||
- | | + | |
public execute() { | public execute() { | ||
$fn = $this-> | $fn = $this-> | ||
$fn(); // This still works | $fn(); // This still works | ||
call_user_func($fn); | call_user_func($fn); | ||
+ | echo is_callable($fn); | ||
+ | echo is_callable_type($fn); | ||
} | } | ||
} | } | ||
+ | |||
</ | </ | ||
In this example, although `$fn` is not a callable that can be passed around to arbitrary scopes, it is valid to call it in the scope that it's in. call_user_func and $fn() will continue to check whether the variable passed in is callable in the current scope. i.e. with is_callable($fn, | In this example, although `$fn` is not a callable that can be passed around to arbitrary scopes, it is valid to call it in the scope that it's in. call_user_func and $fn() will continue to check whether the variable passed in is callable in the current scope. i.e. with is_callable($fn, | ||
+ | ==== The strings ' | ||
- | + | Currently in PHP a callable can be defined using one of these words in place of a classname in a colon separated string like “self:: | |
- | ==== The strings ' | + | |
- | + | ||
- | Currently in PHP a callable can be defined using one of these words in place of a classname in a colon separated string like "self:: | + | |
- | + | ||
- | Because of this | + | |
By replacing the run time evaluation of these with the compile time scope resolution, the variable meaning of the values is removed and replaced with a consistent meaning. | By replacing the run time evaluation of these with the compile time scope resolution, the variable meaning of the values is removed and replaced with a consistent meaning. | ||
+ | To be clear, self:: | ||
- | To be clear, self:: | + | ==== Add a is_callable_type() function ==== |
+ | This RFC proposes adding a separate function from is_callable that can be used to determine if a parameter can be passed as a callable type. | ||
+ | To be clear the meaning of the two functions will be: | ||
- | ==== Instance methods are no longer reported as callable | + | is_callable() - returns true if a the first parameter is callable |
- | <code php> | + | is_callable_type(mixed $var) : bool - returns |
- | class Foo { | + | |
- | function bar() { | + | |
- | echo "this is an instance method"; | + | |
- | } | + | |
- | } | + | |
- | + | ||
- | $callable = [' | + | |
- | var_dump(is_callable($callable)); | + | |
- | + | ||
- | </ | + | |
- | + | ||
- | The output for this is currently | + | |
- | + | ||
- | For an instance method to be a valid callable it will need to be part of a callable that has an instance as the first element in the callable like this: | + | |
- | + | ||
- | <code php> | + | |
- | $foo = new Foo(); | + | |
- | $instanceCallable = [$foo, ' | + | |
- | + | ||
- | var_dump(is_callable($callable)); | + | |
- | </ | + | |
- | + | ||
- | ==== Private and protected functions no longer report as callable for is_callable ==== | + | |
- | + | ||
- | As they are not callable from all scopes, private and protected functions will not be valid methods for the is_callable test, or pass as acceptable for functions that have a parameter that has a callable type. | + | |
- | + | ||
- | It is currently possible using the reflection methods to generate a closure of the private method to allow it to be returned as a callable. If the ' | + | |
<code php> | <code php> | ||
class Foo { | class Foo { | ||
- | + | ||
- | | + | private function |
- | public | + | |
- | $reflection = new ReflectionMethod($this, | + | public function |
- | $callback = $reflection-> | + | |
- | + | | |
- | return $callback; | + | |
- | | + | |
- | + | ||
- | //This will generate a closure to the private method if the ' | + | |
- | //RFC passes | + | |
- | public function | + | |
- | | + | |
- | + | ||
- | | + | |
- | } | + | |
- | + | ||
- | private function somePrivateMethod() { | + | |
- | echo "This is private." | + | |
} | } | ||
} | } | ||
+ | |||
$foo = new Foo(); | $foo = new Foo(); | ||
- | $callback | + | $param = [$foo, ' |
- | $callback(); | + | var_dump(is_callable($param)); |
- | </ | + | $foo-> |
+ | |||
- | This will allow a class to return a private method | + | |
+ | output | ||
+ | |||
+ | false // as the private method | ||
+ | true // as the private method | ||
+ | false // as the private method cannot be passed as a parameter with callable type | ||
- | |||
- | ==== is_callable function change ==== | ||
- | |||
- | Currently the function is_callable has the signature: | ||
- | |||
- | <code php> | ||
- | bool is_callable ( callable $name [, bool $syntax_only = false [, string & | ||
</ | </ | ||
- | which allows users to do this: | + | ==== Instance methods will no longer reported as callable for class names ==== |
<code php> | <code php> | ||
class Foo { | class Foo { | ||
function bar() { | function bar() { | ||
+ | echo "this is an instance method"; | ||
} | } | ||
} | } | ||
+ | |||
+ | $callable = [' | ||
+ | var_dump(is_callable($callable)); | ||
+ | </ | ||
+ | The output for this is currently true, it will be changed to be false. | ||
- | $obj = new Foo(); | ||
- | is_callable([$obj, | ||
- | echo $name; //output is Foo::bar | ||
- | </ | ||
- | The signature will be changed | + | For an instance method to be part of a valid callable it will need to be part of a callable that has an instance as the first element in the callable like this: |
<code php> | <code php> | ||
- | bool is_callable | + | $foo = new Foo(); |
+ | $instanceCallable | ||
+ | |||
+ | var_dump(is_callable($callable)); | ||
</ | </ | ||
- | The `$current_scope` flag will allow users to test whether a parameter is actually invokable in the current scope, even if it is not a parameter that is universally | + | ==== Any additional is_callable cleanup ==== |
+ | |||
+ | Any other errors in is_callable() will be fixed so that if is_callable($fn) returns true, trying to invoke the function directly or through call_user_func() | ||
<code php> | <code php> | ||
- | class Foo { | + | if (is_callable($fn) === true) { |
- | + | $fn(); | |
- | private function bar() {} | + | |
- | + | | |
- | | + | |
- | var_dump(is_callable($param)); | + | |
- | | + | |
- | var_dump(is_callable($param, $syntaxOnly, | + | |
- | | + | |
} | } | ||
- | |||
- | $foo = new Foo(); | ||
- | $param = [$foo, ' | ||
- | |||
- | $foo-> | ||
- | //output will be: | ||
- | //false | ||
- | //true | ||
- | |||
</ | </ | ||
+ | ==== call_user_func equivalence to direct invocation ==== | ||
- | To allow detection | + | The changes in the rest of the RFC should |
+ | ===== Target versions ===== | ||
- | ==== call_user_func equivalence | + | The various things that need to be done to implement this RFC do not need to be all in the same release. There are advantages to having the changes implemented in separate versions. Below is this list of all the changes needed and the target version for them. |
- | The changes in the rest of the RFC should make this goal be achieved. i.e. for any callable that is invokable via `call_user_func($callable); | ||
+ | ==== Add function is_callable_type - 7.4 ==== | ||
- | ===== Target versions ===== | + | ==== Add deprecation notices for self and parent usage in string based callable types e.g. ' |
- | The various things that need to be done to implement this RFC do not need to be all in the same release. There are advantages to having the changes implemented in separate versions. Below is this list of all the changes needed and the target version for them. | + | ==== Add deprecation notices for deprecation notices for self and parent usage in array based callable types e.g. array(' |
- | ==== Soft-deprecate colon separated string callables - 7.2 ==== | + | ==== Remove support for " |
- | Soft-deprecate colon separated string callables | + | ==== Remove support for self and parent names in array(' |
- | ==== Deprecate with notices colon separated string callables | + | Change behaviour of is_callable - 8 |
- | Any usage of a colon separated string callable will generate a E_DEPRECATED notice in the place that they are used, i.e. either | + | Change the behaviour to reflect the new set of things |
- | ==== Deprecate using third parameter | + | ==== Change behaviour |
- | Any call to is_callable that has the 3rd parameter | + | Change the behaviour |
- | ==== Remove colon separated string callables - 8 ==== | + | ===== BC breaks ===== |
- | Any attempt to use " | + | All of the BC breaks are targeted at the PHP 8 release. None of the other changes should have any BC impact, other than the deprecated notices, which will allow people to migrate their code easily. |
- | ==== Remove support for " | ||
- | Although | + | 1. Although |
- | ==== Change behaviour | + | 2. There may be code in the wild that relies on the dynamic meaning |
- | Change the behaviour to reflect the new set of things that are listed as callable above. This is a non-trivial change, and although it would be nice to have it sooner than PHP 8, I can't see any acceptable way to do it without making people angry. | + | <code php> |
+ | ' | ||
- | ==== Change behaviour of ' | + | // change to |
- | Change the behaviour to reflect the new set of things that are listed as callable above. This is a non-trivial change, and although it would be nice to have it sooner than PHP 8, I can't see any acceptable way to do it without making people angry. | + | self:: |
+ | </ | ||
- | ==== Change function signature of is_callable - 8 ==== | ||
- | A comment has been made that changing the signature of this function could be a hard to manage BC break. The position of this RFC is that changing the signature at a major release shouldn' | + | 3. Parent resolution |
- | * no PHP programmer I have spoken to is even aware this function takes 3 parameters. | + | <code php> |
- | * I have not been able to find any code that uses the 3rd parameter. | + | $callable = [FooParent:: |
- | * As we are deprecating all code that uses callables like "self:: | + | // Would need to be replaced with: |
- | ===== BC breaks ===== | + | call_user_func(array(get_parent_class(' |
+ | </ | ||
- | All of the BC breaks are targeted at the PHP 8 release. None of the other changes should have any BC impact, other than the deprecated notices, which will allow people to migrate their code easily. | + | ===== Implementation ===== |
- | 1. Any calls to is_callable that use the `callable_name` parameter would at least need to be wrapped in a version check against the PHP_MAJOR_VERSION number. I believe the amount of code that uses this parameter is minimal. | + | TBD |
- | 2. Any usage of the double-colon separated string as a callable, would need to be changed to an array. | ||
- | 3. Although there are semantic changes to exactly what is a callable, I don't believe these would be that impactful, as the new semantics more closely reflect how people actual use callables. e.g. having a private method report as callable outside of the class where it is defined is just currently not a useful thing, and so I don't think many people will be dependent on that behaviour. | ||
- | 4. There may be code in the wild that relies on the dynamic meaning of ' | ||
- | |||
- | |||
- | ===== Implementation ===== | ||
- | None yet. This could be a large amount of work, so it is appropriate to get feed back on the mailing list before starting this work. The actual change of definition of callable would be a relatively small amount of work. However the SPL libraries make use of colon separated strings (including " |
rfc/consistent_callables.txt · Last modified: 2021/10/20 13:18 by danack