Hello, everyone! Why the print log `A.b` just shows me the hint ‘function myCallback (Kotlin reflect...

# getting-started

[Liberty Tom]

Hello, everyone! Why the print log A.b just shows me the hint ‘function myCallback (Kotlin reflection is not available)’, I want to achieve the A.b print log is similar to the print log A, just like ‘A.b: xxx@yyyyyyy’, how to do it?

[Fergus Hewson]

What are you trying to achieve here?

[Liberty Tom]

I only want to see a print log like A

[Fergus Hewson]

you are printing a different thing, it will never be the same

[Liberty Tom]

Sorry, I want to achieve the A.b print log is similar to the print log A, just like ‘A.b: xxx@yyyyyyy’.

[John Smith]

you are probably looking for java.util.Objects#toIdentityString , not sure how it works on lambdas though

[John Smith]

the default toString method does exactly that

[Klitos Kyriacou]

The reason you're seeing what you're seeing with A is that A doesn't have an overridden toString() method. If you declare it as data object A it will print just like A.b does. If you want it to print the identity hashcode instead, do as John Smith advised.

[Klitos Kyriacou]

By the way, there is no need to do "${A.toString()}" - the idiomatic (and clearer) equivalent is just "$A".

[Szymon Jeziorski]

The message you're seeing in the second println is actually the exact cause of it.
::myCallback is a function reference.
For computing more accurate `toString`s for it, kotlin uses reflection module.
If you had "org.jetbrains.kotlin:kotlin-reflect" in the classpath, you would see something like this for the second `println`:
A.b: fun myCallback(kotlin.String): kotlin.Unit

This is the exact method that's being invoked for you upon ::myCallback toString() invocation:
https://github.com/JetBrains/kotlin/blob/4425f814af8dd848d3f1e51f4ffd7b785dd91b03/[…]s/stdlib/jvm/runtime/kotlin/jvm/internal/FunctionReference.java