Question

I have a Scala domain class (intended for persistence to database)
like:

class Foo() {

var bar: Long = _ // or None or null ???
var jaz: String = _ // or None or null or empty string "" ???
}

How the answer is influenced if the fields bar and jaz are required fields as opposed to
being optional?

Answer 1

From Programming in Scala:

An initializer “= _” of a field
assigns a zero value to that field.
The zero value depends on the field’s
type. It is 0 for numeric types, false
for booleans, and null for reference
types. This is the same as if the same
variable was defined in Java without
an initializer. Note that you cannot
simply leave off the “= _” initializer
in Scala … [as it] would declare an abstract variable, not an uninitialized one

So your code above is the same as

class Foo() {

var bar: Long = 0
var jaz: String = null
}

Kim’s answer sounds correct – if a field is optional, make it an Option, if not, make the constructor set it.