Ask HN: PHP, interfaces, typehinting subtype and LSP?

[enterx]

interface I

{

function foo(stdClass $arg);

}

class Test extends stdClass

{

}

class Implementation implements I

{

function foo(Test $arg)

{

}

}

Result:

Fatal error: Declaration of InterfaceImplementation::foo() must be compatible with I::foo(stdClass $arg) in test.php on line XY

How come that I can't type hint a subtype in the implementation?

[jaachan]

It has to work with all subtypes of stdClass, since in order for the interface to hold its word, I need to be able to get an object thats implements I, and pass it any stdClass, regardless of what they do with it.

[enterx → jaachan]

Based on the research I've made it is legal by the OO principles and SHOULD work but it got omitted somehow in the trade-off during the implementation.

Also NOT available in java.lang.

[jaachan → enterx]

Say I have a function that accepts I as argument:

  function my_func(I $x)
  {
     $x->foo(new stdClass);
  }

That wouldn't be allowed, since your code requires an instance of Test, not stdClass

[FreezerburnV]

This is a question that would be better suited to asking on stackoverflow.com

[enterx → FreezerburnV]

wow. you too might think of allocating unnecessary memory, wasting people's bandwidth and occupying cognitive resources of others for nothing. TIA.

[jaachan → enterx]

It's true though, stack overflow gets you more programmer eyeballs