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How can a parameter's default value reference another parameter? If it cannot, how to work around that?
case class A(val x:Int, val y:Int = x*2)
Error (reasonably enough):
scala> case class B(val x:Int, val y:Int = x*2)
<console>:7: error: not found: value x
case class B(val x:Int, val y:Int = x*2)
^
267
In JavaScript, a parameter has a default value of undefined. It means that if you don't pass the arguments into the function, its parameters will have the default values of undefined .
Default parameter in JavascriptThe default parameter is a way to set default values for function parameters a value is no passed in (ie. it is undefined ). In a function, Ii a parameter is not provided, then its value becomes undefined . In this case, the default value that we specify is applied by the compiler.
In C++, primitive data types (such as int , char , etc.) are pass by value by default. However, they can be passed by reference using the & operator. The non-primitive data types are pass by reference by default, as the reference to the object is passed to the function.
This requires that you use multiple parameter lists:
case class A(x: Int)(y: Int = x*2)
Default values can only refer to parameters in preceding lists.
Be careful however with case classes, because their equality only takes into the account the first parameter list, therefore:
A(1)() == A(1)(3) // --> true!!
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