PHP function parameters defined

class SimpleClass
{
    public $lookup = '';//define property (variable)

    public function displayVar($lookup)
    {
        return $lookup;
    }
}

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Outside the class

$obj = new SimpleClass();
$lookup_input = 1;//1,2 or 3
$return_value = $obj->displayVar($lookup_input); // store output in a variable 

echo return_value;

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http://php.net/manual/en/language.oop5.php

Constants should be defined like below

http://php.net/manual/en/language.oop5.constants.php

Here is the good explanation about visibility

http://php.net/manual/en/language.oop5.visibility.php

I don't understand what you are doing here

class SimpleClass
{
    const $lookupA = 1;
    const $lookupB = 2;
    const $lookupC = 3;

    public function displayVar(llookup*) {
        return $lookup*;
    }
}

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What are you expecting this to do?
You have an illegal parameter variable (llookup*)
You have an illegal return value - which appears to be dynamically targeting a member property which would have to be accessed through $this if you wanted the value.

Nothing about this code looks remotely valid and does not appear to make sense. I might be missing something - can you fill in the gaps.

Sorry!  Just noticed from my previous comment, the return value should have $ symbol. Below is the corrected code.

$obj = new SimpleClass();
$lookup_input = 1;//1,2 or 3
$return_value = $obj->displayVar($lookup_input); // store output in a variable 

echo $return_value;//code updated

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class SimpleClass
{
    // Not a const
    public $lookup = '';//define property (variable)

    public function displayVar($lookup)
    {
        // this just returns the paramter value passed in - it does not touch the 
        // the member property. You need to access that with $this->$lookup;
        return $lookup;
    }
}

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I think this is a misdirection - the author needs to explain what he is trying to do. He appears to be trying to display a class constant by passing an index to the display function - which is not going to work. Before suggesting a solution I recommend we find out what the use case is.

Agreed! But I have mentioned $lookup is a variable in comment, so it is not a constant.  

 public $lookup = '';//define property (variable)

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Sorry, I think its gone off topic.

Using a little more googling Ive managed to do this:-

<?php
class test66 {
    public static $TypehintsBool = "is_bool";
    public static $TypehintsInt = "is_int";
    public static $TypehintsFloat = "is_float";
    public static $TypehintsString = "is_string";
    public static $TypehintsResource = "is_resource";

    public function test($var1) {
        
    }
}

$tt = new test66();
$tt->test(test66::$TypehintsInt);

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My problem is that the test function can accept anything as var1, I would like to limit it to only to accept a range a constant values instead, eg only ($TypehintsBool, $TypehintsInt, $TypehintsFloat, $TypehintsString, $TypehintsResource).

I thought I could test to see if $var1 was allowed by:-

    public function test($var1) {
        if (!is_array($var1,array($TypehintsBool, $TypehintsInt, $TypehintsFloat, $TypehintsString, $TypehintsResource))) {
            die("var1 parameter is not valid");
        }        
    }

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But it didnt work, but with a bit more googling Im sure I could get it to work, however it seems the wrong way to go, surely there is something I can type into the function parameters arguments to limit its selection?

Thank you

if (!is_array($var1,array($TypehintsBool, $TypehintsInt, $TypehintsFloat, $TypehintsString, $TypehintsResource))) 

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Did you mean in_array() - is_array only takes one parameter and its use here makes no sense.

Checking for existence in the function is redundant - if you try and call the function with a non-existing static value it is going to error on you.

This is going to generate an error before you get to the test() function

$tt->test(test66::$NoSuchValue);

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Just for reference and anyone else coming across this thread, this works really nicely:-

<?php
class test66 {
    const TypehintsBool = "is_bool";
    const TypehintsInt = "is_int";
    const TypehintsFloat = "is_float";
    const TypehintsString = "is_string";
    const TypehintsResource = "is_resource";
    public function test($var1) {
        if (!in_array($var1,array(test66::TypehintsBool, test66::TypehintsInt))) { die("\$var1 parameter is not valid"); } 
        echo "Will run this";
    }
}

$tt = new test66();
$tt->test(test66::TypehintsBool);
?>

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@tonelm54,

If you are going to create an array each time to test for existence - why not define the variables as an array to begin with

<?php
class test66 {
	public static $values = array (
		'TypehintsBool' => "is_bool",
		'TypehintsInt' => "is_int",
		'TypehintsFloat' => "is_float",
		'TypehintsString' => "is_string",
		'TypehintsResource' => "is_resource"
	);

	public function test($var1) {
		if (!in_array($var1, test66::$values)) {
			return false;
		}
		return true;
	}
}

$tt = new test66();
if ($tt->test(test66::$values['TypehintsBool'])) {
	echo "Does exist";
}
else {
	echo "Does not Exist";
}
if ($tt->test('abc')) {
	echo "Does exist";
}
else {
	echo "Does not Exist";
}

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Also, consider using return values from your class functions rather than die()

Or even this

<?php
class test66 {
	public static $values = array (
		'TypehintsBool' => "is_bool",
		'TypehintsInt' => "is_int",
		'TypehintsFloat' => "is_float",
		'TypehintsString' => "is_string",
		'TypehintsResource' => "is_resource"
	);

	public function test($var1) {
		if (!isset(test66::$values[$var1])) {
			return false;
		}
		return true;
	}
}

$tt = new test66();
if ($tt->test('TypehintsBool')) {
	echo "Does exist";
}
else {
	echo "Does not Exist";
}

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Saying "in PHP a function can take anything as a parameter" oversimplifies an important issue, one we have been on working with PHP for a long time.  It's variously called "type hinting" or "type declaration."  It's a philosophical conundrum in a loosely-typed language, but the compromise PHP has created works about as well as you can expect if you want backward compatibility.

Here are the most relevant man page links.
http://php.net/manual/en/language.oop5.typehinting.php
http://php.net/manual/en/functions.arguments.php#functions.arguments.type-declaration

This concept is explored a little more in the article here, where we use a RequestArguments class:
https://www.experts-exchange.com/articles/18409/Using-Named-Parameters-in-PHP-Function-Calls.html

@Ray,

Correct me if I am wrong but it is only in PHP7 that type hinting for scalar types is supported - prior to PHP7 wasn't it the case that only objects and arrays were supported for type hinting?

Not an area I am overly familiar with so will take your lead.

Julian: Yes, and PHP 7+ is the only actively supported branch.  PHP < 7 will get security fixes for a while longer, but the new features (including expanded type hints) will only be in PHP 7+.  So, it's time to upgrade!  That's part of the reason I wrote about named parameters in PHP function calls.  It's also a pain to have to remember the order and number of arguments, even if there is type declaration.