Kotlin contains built-in properties and functions that can be used with its various data types. We’ll be looking at the most common built-in property and function for variables of the String type. You can access the full list in Kotlin’s documentation.

In short, a property provides information on a particular value. Kotlin supports a single String property, length which returns the number of characters in a String. Let’s see an example:

val tallestMountain = "Mount Everest" 
print(tallestMountain.length) // Prints: 13

The number of characters in "Mount Everest" equates to 13. Notice how the whitespace is also included in the count.

In addition, a String data type also contains built-in functions that can be used to perform certain actions on the String it’s appended on. For example, the capitalize() function returns a capitalized String:

var name = "codecademy" 
println(name.capitalize()) // Prints: Codecademy 

Note that although the returned value is Codecademy, the original lowercase String, "codecademy", goes unchanged:

println(name) // Prints: codecademy

To persist any changes made by the function, we can reassign the result of name.capitalize() to name and update the variable:

name = name.capitalize()
println(name) // Prints: Codecademy 

Or we can store the result in an entirely new variable:

var capitalizedName = name.capitalize()
println(capitalizedName) // Prints: Codecademy

Note: Characters have their own built-in properties and functions in Kotlin. Reference this page in Kotlin’s documentation for a list of all of them.