Passing $this to a method

[NotionCommotion]

I need a method which accepts an array, and returns the property values of $this who's keys are the values in the array.

 

I am thinking of making it more generic, and instead of using the property values of $this, pass it an object to be used.

 

But this would mean doing the following:

$subset=$this->getObjectSubset($this, ['a','b','c']);

protected function getObjectSubset($source, array $arr)
{
    $obj=new \stdClass;
    foreach($arr as $prop){
        if(isset($source->{$prop})) $obj->{$prop}=$source->{$prop};
    }
    return $obj;
}

Since objects are passed by reference, I guess there is nothing wrong with it.  But it just smells a little wrong passing $this, so would like a second opinion.

 

Thanks

 

[requinix]

Either keep it an instance method and don't pass this, or make it static and do. Probably the former.

 

Or forget the method entirely and go with

$subset = (object)array_intersect_key(get_object_vars($this), array_flip(['a', 'b', 'c']));

[NotionCommotion]

I didn't show it as I didn't think it was relevant, but if the array map was ['a','b','c'=>'d'], I would return (object) ['a' => $this->a, 'b' => $this->b, 'd' => $this->c].  As such, your slick line of code might get a little too complicated.

 

What do you mean by "make it static"?

 

Thanks

[requinix]

Can't find any good explanations of static methods... Wikipedia?

class Math {

	public static function max($a, $b) {
		return $a >= $b ? $a : $b;
	}

}
echo Math::max(1, 2);

static

 

 

 

 

I didn't show it as I didn't think it was relevant, but if the array map was ['a','b','c'=>'d'], I would return (object) ['a' => $this->a, 'b' => $this->b, 'd' => $this->c].  As such, your slick line of code might get a little too complicated.

$subset = (object)array_intersect_key(get_object_vars($this), array_flip(array_keys(['a', 'b', 'c' => 'd']));

[NotionCommotion]

Guess it isn't any more complicated!

 

Yes, I understand static methods.  Why is it okay to pass $this to a static method and not an instance method?

[requinix]

A static method is about doing something without needing access to a particular instance. Math::max does not need an instance of a "Math" class to do its work, so it is static.

An instance method is... not that.

 

Since your method does need $this, or at least its work is dependent upon having an instance of that class, a static method is not as appropriate as an instance method.

protected function getObjectSubset(array $arr)
{
    $obj=new \stdClass;
    foreach($arr as $prop){
        if(isset($this->{$prop})) $obj->{$prop}=$this->{$prop};
    }
    return $obj;
}

Note you don't need {}s for simple dereferencing like you're doing - $this->$prop is fine.

 

[edit] For the record, I'd go for the foreach instead of the one-liner. Easier to read and understand, and it's not like those nested array_* calls will give any big performance boost.

 

[edit 2] That one-liner won't actually do what you want anyways. Forget it.

Edited May 11, 2017 by requinix