Kotlin vs Swift: Comparing Variable Definitions and Property Concepts

Kotlin and Swift have been collaborating in the same development team for a long time, often engaging in technical exchanges (PK). The "Kotlin vs. Swift" series records their dialogues about language differences.

Variable Definition

Kotlin: Kotlin allows concise variable definitions with type inference, e.g., val b = 2, without needing explicit type declarations.

Swift: Swift also supports type inference using let count = 10, which is similar to Kotlin's approach.

Swift uses let for constants and var for mutable variables, and distinguishes between stored properties and computed properties.

Stored property example in Swift: var count = 10 Computed property example in Swift (with custom getter and setter):

var <variableName>: <type> {
    get {
        // statements
    }
    set(newValue) {
        // statements
    }
}

Kotlin’s full property syntax can include optional initializer, getter, and setter:

var <propertyName>[: <PropertyType>] [= <property_initializer>]
    [<getter>]
    [<setter>]

Both languages support type inference, allowing omission of explicit type when an initializer is present, e.g., Kotlin val a: Int = 1 or val b = 2, and Swift let count = 10 or var message = "Hello".

Key Takeaways

Kotlin

Kotlin defines read‑only variables with val and mutable variables with var. Initializer, getter, and setter are optional, and Kotlin does not have a separate concept of computed properties; custom getters/setters are used similarly to Swift.

Swift

Swift defines constants with let and mutable variables with var. It distinguishes stored properties (simple storage) from computed properties (custom getter/setter). Swift also supports type inference, allowing omission of explicit type declarations when an initial value is provided.

For further reading, see the linked articles on Swift & Kotlin comparisons and Swift 4 new features.