Kotlin string interpolation feature explained (with code examples)

The Kotlin string interpolation feature allows you to embed expressions into a string so that you don’t have to concatenate an expression into a string using the + symbol.

For example, when you want to print a variable value with some extra text, you may write the code as shown below:

var myName = "Samwise"

print("Hello, " + myName + "!")

While the code works just fine, you can write a cleaner code using string interpolation as follows:

var myName = "Samwise"

print("Hello, $myName!")

The string interpolation feature allows you to evaluate an expression simply by adding the dollar symbol $ before the variable name.

You also don’t need to exit the string and concatenate the variable using the + symbol with string interpolation.

But keep in mind that when you have an expression that’s more than a single variable name, you need to add curly brackets {} after the $ symbol.

For example, suppose you want to print out the length of the myName variable above. Here’s how you do it:

var myName = "Samwise"

print("myName length is ${myName.length}")
// myName length is 7

The same also applies when you want to do other evaluations, such as adding two numbers together:

var x = 8
var y = 10

print("x + y equals ${x + y}")
// x + y equals 18

Finally, you can also call a function from a string thanks to the string interpolation feature.

The following example calls the sum() function directly inside the print() string argument:

var x = 8
var y = 10

fun sum(a: Int, b: Int): Int {
    return a + b
}

print("x + y equals ${sum(x, y)}")
// x + y equals 18

Now you’ve learned how the string interpolation feature works in Kotlin. Well done! 👍