Why Kotlin function parameter names break the method call?

February 1, 2024

Wonder what is wrong with specifying Kotlin function parameter name when calling a function. In some situation it won’t work and I don’t know how to fix it.

For example, this code works fine without specifying the parameters’ names:

assertEquals(
    FakeDataSource.photosList,
    repository.getMarsPhotos(),
)

But the same code with parameters name give me a compiler error:

assertEquals(
    expected = FakeDataSource.photosList,
    actual = repository.getMarsPhotos(),
)

>Solution :

The Kotlin documentation tells us this:

When calling Java functions on the JVM, you can’t use the named argument syntax because Java bytecode does not always preserve the names of function parameters.

You are calling a JUnit method there, written in Java.