Here's how type inference works in Scala:

Variable Declarations:

When you declare a variable using the val or var keyword without specifying its type, the compiler infers the type based on the assigned value:

val age = 25 // Compiler infers the type as Int

val name = "Alice" // Compiler infers the type as String

Function Definitions:

When you define functions, the compiler infers the parameter types and return type based on the implementation:

def add(a: Int, b: Int) = a + b // Compiler infers parameter and return types as Int

Expressions:

The result of an expression is inferred based on the types of operands and operations:

val result = 3.14 * 2 // Compiler infers the result type as Double

Type Hierarchy:

Scala's type inference system leverages the type hierarchy to infer the most specific common supertype of the involved expressions:

val myList = List(1, 2, 3) // Compiler infers the type as List[Int]

Type Annotations (Optional):

While type inference is powerful, you can still provide explicit type annotations when necessary for clarity or to guide the compiler:

val x: Double = 42.0

Type inference improves code readability, reduces the likelihood of type-related errors, and promotes a more concise coding style. However, there may be cases where you want to provide explicit type annotations for documentation purposes or when the compiler requires more specific information.