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What is the difference between let and var in Swift?

Updated May 17, 2026

Short answer

let defines constants, while var defines mutable variables.

Deep explanation

let ensures immutability after assignment, improving safety and predictability. var allows reassignment. Swift encourages let usage for safer code.

Real-world example

Use let for configuration values like API endpoints, and var for UI state like counters.

Common mistakes

  • Using `var` everywhere, reducing code safety.

Follow-up questions

  • Why does Swift prefer immutability?
  • Can a `let` constant contain mutable objects?

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