Type inference in kotlin

Kotlin is a statically-typed programming language that supports type inference. Type inference is a feature that allows the Kotlin compiler to automatically determine the type of a variable or expression based on its usage and context.

Here's how type inference works in Kotlin:

  1. Initialization: When a variable is declared and initialized with a value, the Kotlin compiler analyzes the value assigned to the variable to determine its type. For example:
val name = "John"

In this case, the compiler infers that the type of the variable name is String because it is initialized with a string literal.

  1. Function Return Types: When a function is defined, the Kotlin compiler can infer the return type based on the expressions used in the function body. For example:
fun add(a: Int, b: Int) = a + b

In this case, the compiler infers that the return type of the add function is Int because the expression a + b evaluates to an integer.

  1. Conditional Expressions: When using conditional expressions like if and when, the Kotlin compiler can infer the common supertype of the possible return types. For example:
fun max(a: Int, b: Int) = if (a > b) a else b

In this case, the compiler infers that the return type of the max function is Int because both the a and b variables are of type Int.

  1. Lambda Expressions: When using lambda expressions, the Kotlin compiler can infer the parameter types and return type based on the context in which the lambda is used. For example:
val numbers = listOf(1, 2, 3, 4, 5)
val evenNumbers = numbers.filter { it % 2 == 0 }

In this case, the compiler infers that the lambda expression { it % 2 == 0 } takes an Int parameter (denoted by the it keyword) and returns a Boolean value.

By leveraging type inference, Kotlin allows developers to write concise and expressive code without sacrificing type safety. The compiler ensures that the inferred types are compatible, reducing the need for explicit type annotations and making code easier to read and maintain.