C#•9mo ago

Using a default implementation on an interface

If I have an interface

interface IAttack<T> {
  T GetAttack();
}

interface IAttack<T> {
  T GetAttack();
}

And I now want to have a specialized interface

interface IUpgradableAttack<T> : IAttack<T>{
  int level {get; set;}
  T GetAttack(int level);
}

interface IUpgradableAttack<T> : IAttack<T>{
  int level {get; set;}
  T GetAttack(int level);
}

Can I somehow use the default implementation GetAttack(){GetAttack(level)} to implement IAttack for thingss that are implementing IUpgradableAttack?

13 Replies

tinOP•9mo ago

If I just put the default implementation inside of IUpgradableAttack, then when implementing that interface the compiler tells me I still need to implement GetAttack (even though there should be a default implementation)

reflectronic•9mo ago

i don't understand the question. what do you want to provide a default implementation for

tinOP•9mo ago

Thanks for answering. Basically what I'd like to do is to have

interface IUpgradableAttack<T> : IAttack<T>{
  int level {get; set;}
  T GetAttack(int level);
  T GetAttack(){
    return GetAttack(level);
  }
}

interface IUpgradableAttack<T> : IAttack<T>{
  int level {get; set;}
  T GetAttack(int level);
  T GetAttack(){
    return GetAttack(level);
  }
}

so that I do not have to implement GetAttack when I have already implemented GetAttack(int level)

reflectronic•9mo ago

yes, the way you must implement it is by writing T IAttack<T>.GetAttack() { ... }

tinOP•9mo ago

Defining the interface as above works. However, when I implement a struct which implements that interface (and does not implement GetAttack), then C# start bugging me

reflectronic•9mo ago

there should be a warning in the code you provided

warning CS0108: 'IUpgradableAttack<T>.GetAttack()' hides inherited member 'IAttack<T>.GetAttack()'. Use the new keyword if hiding was intended.

it's telling you what the issue is-- when you write T GetAttack(), it is not actually an override. it is just a new method also named GetAttack

tinOP•9mo ago

Yup thanks! Just tried it 🙂 I understood my mistake thank you for helping! Maybe one more question in case you know that too. If I now have another method

  struct Attack : IUpgradableAttack<T>{
    public string Describe(){
      var comp = GetComponent();
    }
  }

  struct Attack : IUpgradableAttack<T>{
    public string Describe(){
      var comp = GetComponent();
    }
  }

throws an error, since GetComponent is not implemented and it somehow does not manage to use the default implementation from the interface. Prepending the interface name also does not work. Is there a way to use the default implementation without boxing?

reflectronic•9mo ago

there is a way to do it

private static ??? GetComponent<T, TAttack>(T @this) 
    where T : IUpgradeableAttack<TAttack>
{
    return @this.GetComponent();
}

private static ??? GetComponent<T, TAttack>(T @this) 
    where T : IUpgradeableAttack<TAttack>
{
    return @this.GetComponent();
}

then use GetComponent(this)

tinOP•9mo ago

ah ok haha, if that is the only way I maybe will just write GetComponent(level) for the implementations

reflectronic•9mo ago

yeah, it is a lame workaround

tinOP•9mo ago

ok, nevertheless thank you for answering my questions! helped me a lot Ok, sorry for coming back again. I think this is really the last time. Will this incur boxing at runtime when I want to call that function? Because I will have to now explicitly cast everything as that interface to make it work right? basically asking if there is any allocation happening

reflectronic•9mo ago

oh. um, for a struct, yeah it will there's no way to avoid it. the this inside of the DIM is IUpgradeableAttack

tinOP•9mo ago

hmm ok thats unfortunate then I'm just gonna copy paste the implementation of GetComponent(){ return GetComponent(level);} I guess

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Using a default implementation on an interface