Hi I was wondering if is there a way to create optional meth

Question

Hi I was wondering if is there a way to create optional methods on interfaces like with switf

diesieben07 · Answer

emaleavil I think you would have to move the optional methods to a different interface Then you could do ` myObject as SomeInterface method `

emaleavil · Answer

Thanks for your answer but I refer to methods whose implementation is optional

gildor · Answer

You can add empty default method to interface

gildor · Answer

```interface Foo fun bar fun optionalBaz You can override me but it s not required ```

emaleavil · Answer

ok that s what I need

diesieben07 · Answer

I only looked at the documentation for a brief moments but as I understood it optional methods are optionally implemented With Andrey s example the method is always implemented as there is a default

gildor · Answer

But what is a practical difference

gildor · Answer

I mean empty default method and method that optional to override

emaleavil · Answer

yes you re right but you don t need to override it on every class which implements your interface

diesieben07 · Answer

If there is a Unit return and the method doesn t have side effects Not much difference

gildor · Answer

default method has no side effects

gildor · Answer

at least inside interface

diesieben07 · Answer

`println hello world ` there s your side effect

gildor · Answer

gt but you don t need to override it on every class same for default method

diesieben07 · Answer

I mean yes in most cases you can achieve something similar but it s different

gildor · Answer

I still don t understand difference bitween optionally implementation and empty default method

gildor · Answer

you mean if later someone add some code to empty default method

gildor · Answer

I understand general difference I don t understand difference in this particular case

diesieben07 · Answer

For example yes Maybe I am wrong smile

emaleavil · Answer

Anyway I have to add an empty implementation on every class

emaleavil · Answer

I don t know but I think that it s similar to optional on swift

diesieben07 · Answer

But this approach only really works with methods that return `Unit`

emaleavil · Answer

why I think that if you provide an empty implementation is because you re not interested in consume this method

diesieben07 · Answer

And what do you do if the method returns a String What do you return in the default method You can t use null do you use a special string That would be a nightmare

emaleavil · Answer

I can return an empty string

emaleavil · Answer

because I don t need it

gildor · Answer

But how this thing handled in Swift

gildor · Answer

I mean if you have an optional method and somebody called it

emaleavil · Answer

I don t know

emaleavil · Answer

this is an answer that someone gave me on ios group

emaleavil · Answer

Protocols at least in ObjC don t provide method implementations They only specify the signatures of methods to be implemented by conforming types Optional methods don t provide any empty default impl Instead you call them like this `delegate someOptionalMethod argument 42 ` Note the ` ` which makes sure at runtime that `someOptionalMethod` only gets called if the delegate actually does implement it

diesieben07 · Answer

Thats what I read and what made me suggest the two interface approach

emaleavil · Answer

what happen if are there more than one method in your approach

diesieben07 · Answer

You make more than one interface I realize it s verbose It depends on what exactly your use case is