CODEWITHSUNDEEP
kotlin
Jire
Jire

Reputation: 10290

Kotlin: Method reference not working?

It seems I'm unable to use a method reference of an object in Kotlin. This feature exists in Java.

For example in Java if I was looping through a string to append each character to a writer:

string.forEach(writer::append);

But in Kotlin using the same syntax does not work because:

enter image description here

Upvotes: 23

Views: 17850

Answers (3)

rvazquezglez
rvazquezglez

Reputation: 2454

I am using Kotlin 1.3 and while referencing a Java method I got a very similar error. As mentioned in this comment, making a lambda and passing it to the forEach method is a good option.

key.forEach { writter.append(it) }

Being it the implicit name of a single parameter.

Upvotes: 4

Ilya
Ilya

Reputation: 23115

Starting from Kotlin 1.1 writer::append is a perfectly valid bound callable reference.

However, you still cannot write string.forEach(writer::append) because Writer#append method returns a Writer instance and forEach expects a function that returns Unit.

Upvotes: 10

Andrey Breslav
Andrey Breslav

Reputation: 25767

For now, Kotlin only supports references to top-level and local functions and members of classes, not individual instances. See the docs here.

So, you can say Writer::append and get a function Writer.(Char) -> Writer, but taking a writer instance and saying writer::append to get a function (Char) -> Writer is not supported at the moment.

Upvotes: 26

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