php: issue with the output of var_dump($this)

Question

<?php
class A {
    var $name= 'A';
    function main($objC){
        var_dump($this);B::request('init', $objC);
    }

}
class B {
    var $name= 'B';
    function request($func, $objC){
        if (method_exists($objC, $func)){
            var_dump($this);$objC->$func($this);
        }
    }

}
class C {
    var $name= 'C';
    function init($pobj){       
        var_dump($this);
    }
}
$objA =  new A;
$objB = new B;
$objC = new C;
$objA->main($objC);

Output:

object(A)[1]
  public 'name' => string 'A' (length=1)

object(A)[1]
  public 'name' => string 'A' (length=1)

object(C)[3]
  public 'name' => string 'C' (length=1)

I thought $this in Class B always means the object of that Class B. But seems not, can anyone explain: why var_dump($this); in class B, outputs below result not object(B)?

object(A)[1]
      public 'name' => string 'A' (length=1)

B::request is a static call, not a call to any instance of B, so the var_dump($this) from B has no contect of B being $this — Mark Baker
– Mark Baker, Commented Aug 21, 2013 at 9:33
@MarkBaker oops removed my comment about static, thought the question was why $this is defined. — meze
– meze, Commented Aug 21, 2013 at 9:49

Mark Baker · Accepted Answer · 2013-08-21 09:39:08Z

1

If you run this with full error logging enabled, it will explain why:

Strict Standards: Non-static method B::request() should not be called statically, assuming $this from incompatible context in /php/tests/o2.php on line 6

So basically, use of $this in a statically-called method is meaningless, so PHP actually tries to apply a context.... and looks like it applies $this from the calling method

answered Aug 21, 2013 at 9:39

Mark Baker

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4 Comments

meze Over a year ago

"$this in a statically-called method is meaningless" not always. The error is about incompatible context. If the context is the same, no error will be triggered afaik.

Mark Baker Over a year ago

True: if the context is the same (i.e. I have method request in class A that references $this, and I call it statically from another method in A) then I don't get such a warning because the context isn't incompatible

Mark Baker Over a year ago

I think my point is still valid though: because the context isn't compatible (ie there isn't an instance of B within the call hierarchy that can be referenced) then it's falling back to the previous (incompatible) context. Whatever the case, I wouldn't recommend it as good coding practise.

user2507818 Over a year ago

Thanks. it is helpful. BTW, how to run this with full error logging enabled?

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