learn-co-curriculum / dsc-enterprise-hsbc-scala-apply-method

The Magical apply method

About apply

Considering the following code once again:

class Foo(x:Int) {
   def bar(y:Int) = x + y
}

defined class Foo

If we run it, it would like this and return 50

val foo = new Foo(40)
foo.bar(10)

foo: Foo = Foo@52220d9b
res51: Int = 50

Replacing bar with apply

Let’s take the previous code and use apply instead of bar:

class Foo(x:Int) {
   def apply(y:Int) = x + y
}

defined class Foo

If we run it, it would like this and return 50

val foo = new Foo(40)
foo.apply(10)

foo: Foo = Foo@783d1bad
res53: Int = 50

Where thing are different, is that apply is not a required method call and you can leave the word apply out!

Therefore…​since we used apply it looks like this:

val foo = new Foo(40)
foo(10)

foo: Foo = Foo@22c91f2c
res54: Int = 50

apply Conclusion

• If the method is called apply, no matter where it was defined, you can leave the explict call out!
• This is probably one of the most important aspects to the language that few know about since it too many it is too obvious too mention