Scala | String Interpolation

String Interpolation refers to substitution of defined variables or expressions in a given String with respected values. String Interpolation provides an easy way to process String literals. To apply this feature of Scala, we must follow few rules:

1. String must be defined with starting character as s / f /raw.
2. Variables in the String must have ‘$’ as prefix.
3. Expressions must be enclosed within curly braces ({, }) and ‘$’ is added as prefix.

Syntax:

// x and y are defined
val str = s"Sum of $x and $y is ${x+y}"

Types of String Interpolator

1. s Interpolator: Within the String, we can access variables, object fields, functions calls, etc.

   Example 1: variables and expressions:

   // Scala program
   // for s interpolator
   
   // Creating object
   object GFG
   {
       // Main method
       def main(args:Array[String])
       {
   
           val x = 20
           val y = 10
   
           // without s interpolator
           val str1 = "Sum of $x and $y is ${x+y}"
   
           // with s interpolator
           val str2 = s"Sum of $x and $y is ${x+y}"
   
           println("str1: "+str1)
           println("str2: "+str2)
       }
   }

   Output:

   str1: Sum of $x and $y is ${x+y}
   str2: Sum of 20 and 10 is 30

   Example 2: function call

   // Scala program
   // for s interpolator
   
   // Creating object
   object GFG
   {
       // adding two numbers
       def add(a:Int, b:Int):Int
       =
       {
           a+b
       }
   
       // Main method
       def main(args:Array[String])
       {
   
           val x = 20
           val y = 10
   
           // without s interpolator
           val str1 = "Sum of $x and $y is ${add(x, y)}"
   
           // with s interpolator
           val str2 = s"Sum of $x and $y is ${add(x, y)}"
   
           println("str1: " + str1)
           println("str2: " + str2)
       }
   }

   Output:

   str1: Sum of $x and $y is ${add(x, y)}
   str2: Sum of 20 and 10 is 30

2. f Interpolator: This interpolation helps in formatting numbers easily.

   To understand how format specifiers work refer Format Specifiers.

   Example 1: printing upto 2 decimal place:

   // Scala program
   // for f interpolator
   
   // Creating object
   object GFG
   {
       // Main method
       def main(args:Array[String])
       {
   
           val x = 20.6
   
           // without f interpolator
           val str1 = "Value of x is $x%.2f"
   
           // with f interpolator
           val str2 = f"Value of x is $x%.2f"
   
           println("str1: " + str1)
           println("str2: " + str2)
   
       }
   }

   Output:

   str1: Value of x is $x%.2f
   str2: Value of x is 20.60

   Example 2: setting width in integers:

   // Scala program
   // for f interpolator
   
   // Creating object
   object GFG
   {
       // Main method
       def main(args:Array[String])
       {
   
           val x = 11
   
           // without f interpolator
           val str1 = "Value of x is $x%04d"
   
           // with f interpolator
           val str2 = f"Value of x is $x%04d"
   
           println(str1)
           println(str2)
       }
   }

   Output:

   Value of x is $x%04d
   Value of x is 0011

   If we try to pass a Double value while formatting is done using %d specifier, compiler outputs an error. In case of %f specifier, passing Int is acceptable.

3. raw Interpolator: String Literal should start with ‘raw’. This interpolator treats escape sequences same as any other character in a String.
   Example :printing escape sequence:

   // Scala program
   // for raw interpolator
   
   // Creating object
   object GFG
   {
       // Main method
       def main(args:Array[String])
       {
   
           // without raw interpolator
           val str1 = "Hello\nWorld"
   
           // with raw interpolator
           val str2 = raw"Hello\nWorld"
   
           println("str1: " + str1)
           println("str2: " + str2)
       }
   }

   Output:

   str1: Hello
   World
   str2: Hello\nWorld