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+====== Request for Comments: Remove calls with incompatible Context ======
+An RFC for deprecating and removing <php>$this</php> from incompatible context.
+  * Version: 1.0
+  * Date: 2012-07-30
+  * Author: Gustavo Lopes
+  * Status: Voting phase
+  * First Published at: http://wiki.php.net/rfc/incompat_ctx
+===== Introduction =====
+This RFC proposes deprecating (in PHP 5.5) and removing (in the next version) the "<php>$this</php> from incompatible context" feature.
+===== What this proposal is not about =====
+This proposal is not about removing static calls to instance methods or instance-like calls to static methods.
+===== The feature =====
+To be clear, the feature I'm proposing to remove is this:
+<code php>
+class A {
+    function foo() { var_dump(get_class($this)); }
+}
+class B {
+   function bar() { A::foo(); }
+}
+$b = new B;
+$b->bar(); //string(1) "B"
+</code>
+Internal methods cannot be called in this fashion.
+===== The Change ====
+Even though I think an error at call site would be the most useful to the user, the most sensible option is to just have <php>$this === null</php> inside the callee, like when you do:
+<code php>
+class A { function foo() {} }
+A::foo(); // E_STRICT
+</code>
+===== Rationale =====
+Method implementations almost always assume that $this refers to an instance of a compatible type. When they are called with an incompatible <php>$this</php>, there'll a bug most of the time. The only warning is an <php>E_STRICT</php> message, which many people have disabled.
+Because this feature is surprising and little-known, a simple error like calling Class::foo() instead of ::fooStatic() (when foo() and fooStatic() have similar names), by not failing on the call site, can be difficult to identify.
+When combined with LSB, it can be even more difficult to identify. See https://bugs.php.net/bug.php?id=62446
+===== BC break =====
+The break should be minor. I very much doubt there are many lines of code that rely on this feature. It has been discouraged with an <php>E_STRICT</php> since 2006 (see [[https://github.com/php/php-src/commit/6f76b170|6f76b170]]).
+This feature, as noted in the [[http://lxr.php.net/xref/PHP_TRUNK/Zend/zend_vm_def.h?r=80497ea7dfade2ccd032ef65103c0a113338653a#2335|comment]], exists only for compatibility with PHP 4. Far more used legacy features, like register globals, have already been axed.
+This feature can, however, be used to implement trait-like behavior, and I'm sure someone somewhere did such a thing.
+===== Alternatives =====
+Using traits is perhaps the easiest and cleanest way to replace code that relies on the feature to be removed. Changing the code to use traits implies: 1) refactoring the instance methods called from incompatible contexts into a trait, 2) make the callers from incompatible contexts use the new trait, 3) change the call sites to use <php>$this->method()</php> instead of <php>OrigClass::method()</php>. Example:
+<code php>
+<?php
+class A {
+	function dumpClass() {
+		var_dump(get_class($this));
+	}
+}
+class B {
+	function test() {
+		A::dumpClass();
+	}
+}
+$a = new A;
+$b = new B;
+$a->dumpClass();
+$b->test();
+</code>
+would become:
+<code php>
+<?php
+trait ATrait {
+	function dumpClass() {
+		var_dump(get_class($this));
+	}
+}
+class A {
+	use ATrait;
+}
+class B {
+	use ATrait;
+	function test() {
+		$this->dumpClass();
+	}
+}
+$a = new A;
+$b = new B;
+$a->dumpClass();
+$b->test();
+</code>
+A worse solution, which relies on the possibility of calling instance methods statically would be using an extra parameter:
+<code php>
+<?php
+class A {
+	function dumpClass($obj=null) {
+		if ($obj === null)
+			$obj = $this;
+		var_dump(get_class($obj));
+	}
+}
+class B {
+	function test() {
+		A::dumpClass($this); //E_STRICT ($this would be NULL on callee)
+	}
+}
+$a = new A;
+$b = new B;
+$a->dumpClass();
+$b->test();
+</code>
+===== Vote =====
+Voting ends not before Monday, January 28th 2013. The PHP language is ultimately changed, so a 2/3 majority is required.
+<doodle
+title="Deprecate calls with incompatible context in 5.5 and disallow them in the version after (be it 5.6 or 6.0)" auth="cataphract" voteType="single" closed="False">
+   * Yes
+   * No
+</doodle>
+===== Changelog =====
+  * 2012-07-30: Initial version
+  * 2012-01-20: Opened vote

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