Defs in scala

defs.scala

// In scala a def (called a "method") is defined as follows:

    def foo(arg: String): Int = expr
//  ^   ^  ^^    ^        ^     ^
//  ^   ^  ^^    ^        ^     an expression, whose type must match the declared return type, if specified
//  ^   ^  ^^    ^        ^     
//  ^   ^  ^^    ^        the declared return type (optional).
//  ^   ^  ^^    ^        
//  ^   ^  ^^    the type of each argument must be declared
//  ^   ^  ^^
//  ^   ^  ^each argument must be named
//  ^   ^  ^
//  ^   ^  zero or more "argument lists". Each argument list may have zero or more arguments
//  ^   ^
//  ^   the identifier (i.e. the name of the method) 
//  ^
//  start with the keyword def

// Arguments may be given default values:

    def driversLicense(tpe: String = "Standard: Cars")

// We "call" a method by providing values for the arguments:

    driversLicense()                           //we can omit arguments if there are default values
    driversLicense("HGV")
    driversLicense(tpe = "Motorcycle < 125cc") //we can specify arguments by name

// It is idiomatic to specify arguments by name when they are booleans. E.g.

    close(ignoreExceptions = true) //correct
    close(true)                    //sadface

// We may declare defs within defs

    def add(i: Int, j: Int) = {
      def addI(j: Int) = j + i //Question: what value does j have here?
      addI(j)
    }

// "Variable shadowing". In the above definition, we use the name "j" twice. We say that the inner definition "shadows" the outer one.
// It may be a source of confusion but it is unambiguous; the definition in the closest enclosing scope is used

// We may omit the braces for methods composed of a single line, or unambiguous expression:

    def add(i: Int, j: Int) = i + j