Can PHP parse native syntax?

Question

Can PHP parse native syntax? For example, I would like to write a function that takes an input, such as $object->attribute , and tells itself:

OK, he gives me $foo->bar , which means that he should think that $foo is an object that has the bar property. Before trying to access bar and potentially get the message “Trying to get a non-object property”, let me check if $foo even an object.

The ultimate goal is to echo the value if it is set, and fails if not .

I want to avoid repeating as follows:

 <input value="<? if(is_object($foo) && is_set($foo->bar)){ echo $foo->bar; }?> "/> 

... and to avoid writing a function that does the above, but must have an object and attribute passed separately, for example:

 <input value="<? echoAttribute($foo,'bar') ?>" /> 

... but instead write something that:

• saves the syntax of the attribute object->
• is flexible: can also handle array keys or regular variables

Like this:

 <input value="<? echoIfSet($foo->bar); ?> /> <input value="<? echoIfSet($baz['buzz']); ?> /> <input value="<? echoIfSet($moo); ?> /> 

But it all depends on how PHP can tell me "what I ask when I say $object->attribute or $array[$key] ", so that my function can handle each in its own type.

Is it possible?

Update

Here I got some good answers and experimented a bit. I wanted to take stock.

• The answer to my original question seems to be no, but we found a way to do this, I tried to do it. Techpriester pointed out that I can pass the string '$ foo-> bar' to the function and parse it and eval() . Not the approach I want to take, but deserves a mention.
• Peter Bailey noted that something like $foo->bar is evaluated before passing the function. I should have thought about it, but for some reason I didn’t. Thanks Peter!
• Will Vousden showed that passing $foo->$bar by reference allows the function to evaluate it, rather than evaluate it in advance. Its function shows that isset($foo->bar) will not complain if $foo not an object that I did not know about.

More interestingly, his example seems to imply that PHP is waiting to evaluate a variable until it is absolutely required.

If you pass something by value , then of course PHP must define the value . Like this:

 $foo->bar = 'hi'; somefunction($foo->bar); // same as somefunction('hi'); 

But if you pass by reference , it can wait to determine the value when it is really needed.

Like this (following the order in which events occur):

 echo ifSet($foo->bar); // PHP has not yet evaluated $foo->bar... function ifSet(&$somevar){ // ...because we're passing by reference (&$somevar) // Now we're inside the function, but it still hasn't evaluated $foo->bar; it // just made its local variable, $somevar, point to the same thing as $foo->bar if(isset($somevar)){ // Right HERE is where it evaluated - when we need it return $bar; } } 

Thanks to all who responded! If I distorted something, let me know.

Answer 1

You can pass it by the link:

 <?php function foo(&$bar) { if (isset($bar)) { echo "$bar\r\n"; } else { echo "It not set!\r\n"; } } $baz = new stdClass; $baz->test = 'test'; foo($baz->test); foo($baz->test2); $baz = array(); foo($baz['test3']); ?> 

Note that this will not work if you try to access the object as an array or vice versa.

You should not rely too much on something like that too.

Answer 2

perhaps in this particular case you can use the @ symbol:

 <input value="<?php echo @$foo->bar; ?> "/> 

Answer 3

The reason you can never do something like this

 echoIfSet($foo->bar); 

Because $foo->bar is evaluated before it is sent to the function. If this value is a string, all echoIfSet() will see the string - it does not know that the string is obtained from the object property.

So no , in a word. PHP cannot "parse its own syntax"

Every option you have (using __get () / __ set () or Reflection) involves more code and work than what you are trying to avoid - and they still don't give you exactly what you want .

Answer 4

Wrapping your array and objects in a special array. you can use properties using php magic methods.

 class wrap implements ArrayAccess{ private $fields=array(); function __get($name){ if(isset($this->fields[$name])){ return $this->fields[$name]; } } function __set($name, $value){ $this->fields[$name] = $value; } // with function isset() public function offsetExists($offset) { return isset($this->$fields[$offset]); } public function offsetGet($offset) { return $this->$fields[$offset]; } public function offsetSet($offset, $value) { return $this->$fields[$offset] = $value; } public function offsetUnset($offset) { unset($this->$fields[$offset]); } } 

This will allow you to do whatever you need.

Answer 5

There is a language function that will execute any PHP code that you pass to it as a string: eval() .

But you really, really (like in "I'm Dead Seriously") should not use it. This causes far more problems than it solves and makes your code indispensable.

Generally, a better and cleaner way.

"eval ()" leads to the dark side of the force, I mean PHP.

If you just need the "obj" part and the "attribute" of the supplied string, a regular expression can do this. It will be something like "/\$(\w+)->(\w+)/" . You can pass this to preg_match() and it will provide you with string components.

Answer 6

Are you just looking for an eval instruction?

Answer 7

If you are looking for something that gives you the name of the variable you were passing in, for example:

 function foo($variable) { echo variableName($variable); } $test = "Hello World"; // echoes "test" foo($test); 

Then you will not find it. PHP does not have this capability.