Scala | Functions Call-by-Name

08 Apr, 2019
In Scala when arguments pass through call-by-value function it compute the passed-in expression’s or arguments value once before calling the function . But a call-by-Name function in Scala calls the expression and recompute the passed-in expression’s value every time it get accessed inside the function. Here example are shown with difference and syntax.
This method uses in-mode semantics. Changes made to formal parameter do not get transmitted back to the caller. Any modifications to the formal parameter variable inside the called function or method affect only the separate storage location and will not be reflected in the actual parameter in the calling environment. This method is also called as call by value.
Syntax :
def callByValue(x: Int)
// Scala program of function call-by-value  // Creating objectobject GFG {    // Main method    def main(args: Array[String])     {        // Defined function        def ArticleCounts(i: Int)         {            println("Tanya did article " +                    "on day one is 1 - Total = " + i)            println("Tanya did article " +                    "on day two is 1 - Total = " + i)            println("Tanya did article "+                     "on day three is 1 - Total = " + i)            println("Tanya did article " +                    "on day four is 1 - Total = " + i)        }          var Total = 0;                  // function call        ArticleCounts         {            Total += 1 ; Total                      }    }}
Tanya did article on day one is 1 - Total = 1
Tanya did article on day two is 1 - Total = 1
Tanya did article on day three is 1 - Total = 1
Tanya did article on day four is 1 - Total = 1

Here, by using function call-by-value mechanism in above program total count of article not increased.
A call-by-name mechanism passes a code block to the function call and the code block is complied, executed and calculated the value. message will be printed first than returns the value.Syntax :
def callByName(x: => Int)
Example :
// Scala program of function call-by-name  // Creating objectobject main {    // Main method    def main(args: Array[String])    {        // Defined function call-by-name        def ArticleCounts(i: => Int)         {            println("Tanya did articles " +                     " on day one is 1 - Total = " + i)            println("Tanya did articles "+                     "on day two is 1 - Total = " + i)            println("Tanya did articles " +                     "on day three is 1 - Total = " + i)            println("Tanya did articles " +                     "on day four is 1 - Total = " + i)        }          var Total = 0;                  // calling function        ArticleCounts         {            Total += 1 ; Total        }}}
Tanya did articles  on day one is 1 - Total = 1
Tanya did articles on day two is 1 - Total = 2
Tanya did articles on day three is 1 - Total = 3
Tanya did articles on day four is 1 - Total = 4

Here, by using function call-by-name mechanism in above program total count of article will increased.Another program of function call-by-name.
Example :
// Scala program of function call-by-name  // Creating objectobject GFG{    // Main method    def main(args: Array[String])    {        def something() =         {            println("calling something")            1 // return value        }                  // Defined function        def callByName(x: => Int) =         {            println("x1=" + x)            println("x2=" + x)         }                  // Calling function        callByName(something)    }}
calling something
x1=1
calling something
x2=1

Picked
Scala
Scala-Method
Scala
Writing code in comment?
Please use ide.geeksforgeeks.org,
generate link and share the link here.
Class and Object in Scala
Type Casting in Scala
Scala List filter() method with example
Scala Map
Scala Tutorial – Learn Scala with Step By Step Guide
Scala Lists
Operators in Scala
Scala | Arrays
Scala Constructors
Inheritance in Scala