1.6 The apply Method
In Scala, it is common to use a syntax that looks like a function call. For example, if s is a string, then s(i) is the ith character of the string. (In C++, you would write s[i]; in Java, s.charAt(i).) Try it out in the REPL:
"Hello"(4) // Yields 'o'
You can think of this as an overloaded form of the () operator. It is implemented as a method with the name apply. For example, in the documentation of the StringOps class, you will find a method
def apply(n: Int): Char
That is, "Hello"(4) is a shortcut for
When you look at the documentation for the BigInt companion object, you will see apply methods that let you convert strings or numbers to BigInt objects. For example, the call
is a shortcut for
It yields a new BigInt object, without having to use new. For example:
BigInt("1234567890") * BigInt("112358111321")
Using the apply method of a companion object is a common Scala idiom for constructing objects. For example, Array(1, 4, 9, 16) returns an array, thanks to the apply method of the Array companion object.