Question

I received the error while trying to display some variable like so:

echo "id is $url->model->id";

The problem seems to be that echo only likes simple variables to be displayed in this way (like $id or $obj->id).

class url {
    public function  __construct($url_path) {
        $this->model = new url_model($url_path);
    }
}

class url_model {
    public function  __construct($url_path) {
        $this->id = 1;
    }
}

and then

$url = new url();
echo "id is $url->model->id"; // does not work

$t = $url->model->id;
echo "id is $t";  //works

$t = $url->model;
echo "id is $t->id";  //works

echo "id is {$url->model->id}"; //works. This is the same syntax used to display array elements in php manual.

//php manual example for arrays
echo "this is {$baz['value']}";

I don’t know why it works, I just guessed the syntax.

In php manual it doesn’t say how to use echo "..." for objects. Also there is some strange behavior: echo on simple vars, works; echo on simple property of an object works; echo on simple property of an object that is inside another object does not work.

Is this echo "id is {$url->model->id}"; the right way? Is there a simpler way?

Answer 1

"{$var}" is the universal string variable interpolation syntax. There are some syntax shortcuts known as simple syntax for things like one-dimensional arrays:

echo "$arr[foo]";

This does not work for multi-dimensional arrays though, e.g. "$arr[foo][bar]". It’s simply a hardcoded special case. The same is true for objects. "$obj->foo" is a hardcoded special case that works, while more complex cases will have to be handled by the complex "{$obj->foo->bar}" syntax.