Dog.groovy

class Dog {
    final String name

    Dog(String name) {
        this.name = name
    }

    @Override
    public int hashCode() {
        return name.hashCode()
    }
}

main.nf

#!/usr/bin/env nextflow
nextflow.enable.dsl=2

import Dog

process Woof {
    input:
    val(dog)

    "echo ${dog.name} says woof! > bark_book.txt"
}

workflow {
    Channel.from( "Fido", "Spot", "Lassie", "Barky" ) | map { new Dog(it) } | Woof
}