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Date: Sun, 5 Jun 2005 20:48:57 +0200
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Message-ID: <200506052048.58029.johannes@php.net>
Subject: incrementing boolean values
From: johannes@php.net (Johannes Schlueter)

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Hi,

PHP is a weak-typed language which casts in the background as required - at=
=20
least most of the time. I recently found an exception which bugged me:

  $a =3D false;
  $a++;

Here $a isn't casted to int or "incremented" to true but the incrementing h=
as=20
no effect. By checking zend_operators.c I saw that booleans had no explicit=
=20
incrementing rule but uses just the default in the relevant switch.

Looking a bit deeper it got quite interesting: NULL++ gives as result the=20
integer one. This is fine for incrementing undefined variables but imho=20
inconsistent with the behavior of false. NULL-- evaluates to NULL similar t=
o=20
false but different from NULL++.

All this makes using PHP harder than needed. At least I spent quite some ti=
me=20
finding that my variable was set to false instead of 0 (or NULL).

I wrote the attached patch which allows in-/decrementing of simple types by=
=20
casting bools and NULL to long. Yes, it would be a BC break but I don't thi=
nk=20
someone relies on false++ being false and it would make life simpler.

Comments?

johannes

P.S. If the patch doesn't come through: It's available via web, too:=20
http://www.schlueters.de/zend_incdec_with_bool.diff
=2D-=20
Johannes Schl=FCter                           Mayflower GmbH / ThinkPHP
http://thinkphp.de                            http://blog.thinkphp.de

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Index: Zend/zend_operators.c
===================================================================
RCS file: /repository/ZendEngine2/zend_operators.c,v
retrieving revision 1.205
diff -u -p -r1.205 zend_operators.c
--- Zend/zend_operators.c	8 Apr 2005 14:33:00 -0000	1.205
+++ Zend/zend_operators.c	31 May 2005 10:40:11 -0000
@@ -1679,6 +1679,10 @@ ZEND_API int increment_function(zval *op
 		case IS_DOUBLE:
 			op1->value.dval = op1->value.dval + 1;
 			break;
+		case IS_BOOL:
+			op1->value.lval++;
+			op1->type = IS_LONG;
+			break;
 		case IS_NULL:
 			op1->value.lval = 1;
 			op1->type = IS_LONG;
@@ -1736,6 +1740,14 @@ ZEND_API int decrement_function(zval *op
 		case IS_DOUBLE:
 			op1->value.dval = op1->value.dval - 1;
 			break;
+		case IS_BOOL:
+			op1->value.lval--;
+			op1->type = IS_LONG;
+			break;
+		case IS_NULL:
+			op1->value.lval = -1;
+			op1->type = IS_LONG;
+			break;
 		case IS_STRING:		/* Like perl we only support string increment */
 			if (op1->value.str.len == 0) { /* consider as 0 */
 				STR_FREE(op1->value.str.val);

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