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--- rfc:parameter_type_casting_hints [2012/03/04 00:38] – created ircmaxell
+++ rfc:parameter_type_casting_hints [2012/03/04 01:27] – [Cast Type Definitions] ircmaxell
@@ Line 13: / Line 13: @@
 ==== Philosophy ====
+This RFC discusses a method of adding scalar type hints to PHP while attempting to embrace the dynamic nature of PHP variables.  This means that passing a type that does not match the hinted type will cause a cast to happen (if possible, based on the normal type-casting rules used in other areas of the engine).
-==== More ====
+===== Implementation =====
-===== Changelog =====
+==== Syntax ====
+The parameters are type hinted using the following syntax:
+<?php
+    function test((int) $intParam, (string) $strParam = "foo", (array) $array) {}
+?>
+This will cause the following function to always return true for almost any combination of parameters:
+<?php
+    function test((int) $int, (float) $float, (bool) $bool, (string) $string) {
+        return is_int($int) && is_float($float) && is_bool($bool) && is_string($string);
+    }
+?>
+The one exception which will cause the function to not return true, is when the ''$string'' parameter is an object which does not implement __toString, which therefore will throw a Catchable fatal error on conversion to string.  This is the default casting behavior for strings.
+==== Cast Options ====
+The following cast types are supported as parameter casts:
+  * ''(int)'' - Cast to an integer (if not already)
+  * ''(float)'' - Cast to a float (if not already)
+  * ''(bool)'' - Cast to a boolean (if not already)
+  * ''(string)'' - Cast to a string (if not already)
+  * ''(array)'' - Cast to an array (if not already)
+  * ''(object)'' - Cast to an object (if not already)
+Note that the final 2 options (array and object) are there for both completeness, and to provide a less-strict type-hint (to be consistent with the new additions).
+==== Backwards compatibility breaks ====
+This patch does not break existing functionality (with one exception of a C level API change that is not a public API).  Current code will execute as normal.
+===== Patch Details =====
+==== Cast Type Definitions ====
+The patch adds a series of "cast" definitions to the C type constants currently in use by the core.  They are implemented in a way that the destination type of the cast can be found by masking the cast against 0x0F.  They are:
+  * ''IS_NULL_CAST 0x010''
+  * ''IS_LONG_CAST 0x011''
+  * ''IS_DOUBLE_CAST 0x012''
+  * ''IS_BOOL_CAST 0x013''
+  * ''IS_ARRAY_CAST 0x014''
+  * ''IS_OBJECT_CAST 0x015''
+  * ''IS_STRING_CAST 0x016''
+These are used to distinguish casting declarations in OPCode from a possible future implementation of more strict casts.
+These have also been added to the ''zend_get_type_by_const()'' function to return the cast string that would be used.
+==== API Changes ====
+One API change was necessary for the cast to work.  The third paramater of ''zend_verify_arg_type'' was changed from a single pointer zval, to a double pointer zval.  This allows the argument to be separated if the cast happens and a copy-on-write event to be triggered.  All implementations of this function in trunk have been updated (only occurs in the Zend directory).
+==== References ====
+To prevent odd behavior, it is a ''E_COMPILE_ERROR'' to define a parameter as both cast-hinted and a reference.  This prevents issues where passing a variable to a function by reference changes the type of the original argument and possibly destroys data in the original variable.
+==== Default Values ====
+For consistency, only matching types are allowed to be the default to a type-casted parameter.  So ''(int) $foo = null'' and ''(int) $foo = 1'' are both supported, but ''(int) $foo = "1"'' will generate an ''E_COMPILE_ERROR''.
+==== Parser Tokens ====
+No new parser tokens or reserved words are created by this RFC / implementation.
+===== Changelog =====

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