Re: Class privacy and variable identifiers

David Morse wrote: > I have two somewhat general questions about the PHP 5 > language. These points remain unclear to me after reading > the manual and working with the language for a few months: > > i) Does the language provide a way to generate a private or > local class that is accessible only within another function > or a parent class. no. classes are global. as an aside there *may* be namespaces in php in the future. In python, for example, if you declare a > class or function within a function definition, I believe it > is accessible only within the parent function. Does PHP 5 > supply a good way to generate a little utility class without > polluting the public namespace? Or are local variables in > functions, class methods and class properties the only > entities that can be hidden from public access? no - may an assoc array would suffice your needs? many people use static classes to contain sets of [utility] functions as a sort of poormans namespacing ... helps to cut down pollution a little. > > ii) Suppose I would like to be able generate any of several > classes at runtime, for which constructor interfaces are the > same. These might, for example, be specialized subclasses of > a common parent. Based on the idea of a variable variable, > I am tempted to try to replace the class name by a variable, > as in > > $object = new $class_name_variable($param1,$param2,....) works. > > Is this legal PHP 5? Put another way, are variable names the > only identifiers that can be replaced by string values of > other variables, or is the technique more general? For instance, > how about accessing a property or method by a name that is > specified by a variable, as in: > > $object_instance->$property_name_variable works. > > or > > $object_instance->$method_name_variable() works. please get into the habit of testing stuff like this (get yourself a linux shell and read up on using php on the cmdline :-): php5 -r ' class myObject { const MY_CNST = "a"; public $myProp = "b"; public function myMethod() { return "c1"; } public static function myStaticMethod() { return "c2"; } } $f = "MY_CNST"; $c = "myObject"; $p = "myProp"; $m = "myMethod"; $s = "CNST"; $MY_CNST = "f"; print_r($o = new $c()); echo join(", ", array( constant(get_class($o)."::${${"MY_$s"}}"), $o->$p, $o->$m(), constant("$c::MY_CNST"), $o->{"myProp"}, call_user_func(array($c, "myStaticMethod")))),"\n"; ' > > The idea of a 'variable variable' name seems quite useful, be careful with varvars ;-) see also: http://php.net/call_user_func http://php.net/call_user_func_array > but I'm not sure how general the concept is. Is there a > well-defined rule for when the parser will accept a string > value of a variable as a replacement for a literal > identifier. If so, is the rule documented? somewhere on php.net no doubt :-/ > > Thanks in advance for any insight. > > -David Morse