Is it possible to extend a method within an extended scala class? - scala

Question

Assume I have the following scala classes, is it possible to extend a function on SecondClass and add more code to it? (possibly chained to another function within the function i'd like to extend)
package io.gatling.http.check
class FirstClass {
def login() = {
exec(http("Login")
.post("anonymous/login")
.body(ElFileBody("rest/UserAnonymousLogin.json")).asJson
}
}
I would like to extend the login function with the following (.check(status is 200)
class SecondClass extends FirstClass {
def login() = {
.check(status is 200))
}
}
Is that possible?

Answer 1

The syntax you're looking for is
class X {
def go(a: Int) = ???
}
class Y extends X {
override def go(a: Int) = {
val u = super.go(a)
// do things with `u` and return whatever
}
}
You'll need to do a little refactoring to get your code in this shape. I envisage
class FirstClass {
def body = ElFileBody("rest/UserAnonymousLogin.json")
// stuff that calls `body`
}
class SecondClass {
override def body = super.body.check(status is 200)
// no need to redefine stuff as it's inherited from `FirstClass`
}

Answer 2

Given checks method accepts a variable number of HttpCheck, that is, HttpCheck*
def check(checks: HttpCheck*): HttpRequestBuilder
consider refactoring FirstClass to
class FirstClass {
def login(checks: HttpCheck*) = {
exec(http("Login")
.post("anonymous/login")
.body(ElFileBody("rest/UserAnonymousLogin.json")).asJson
.check(checks: _*)
)
}
}
Note how by default we pass no checks when calling (new FirstClass).login().
Now derived classes could pass in a checks to be performed like so
class SecondClass extends FirstClass {
def loginWithStatusCheck() = {
super.login(status is 200)
}
}
Note we are not actually overriding FirstClass.login here.
Another approach instead of overriding could be functional composition, for example, we break down the problem into smaller functions
val buildClient: String => Http = http(_)
val buildPostRequest: Http => HttpRequestBuilder = _.post("anonymous/login").body(ElFileBody("rest/UserAnonymousLogin.json")).asJson
val checkStatus: HttpRequestBuilder => HttpRequestBuilder = _.check(status is 200)
and then compose them
exec((buildClient andThen buildPostRequest andThen checkStatus)("Login"))
Now we can simply add further steps to the composition instead of worrying about class hierarchies and overriding.