Cannot assign value of type '...' to type '...'

The “Cannot assign value of type” error occurs when you try to assign a value of one type to a variable declared with a different type. Swift is a type-safe language and does not perform implicit type conversions.

What It Means

Swift enforces strict type checking at compile time. Every variable and expression has a known type, and assignments must match that type exactly. If you try to assign an Int to a String variable, or a Float to an Int variable, the compiler rejects the code with this error.

Why It Happens

• Numeric type mismatch — assigning an Int to a Double variable or vice versa.
• Missing explicit cast — a method returns Any or AnyObject and you assign it to a typed variable.
• Wrong type annotation — you declared a variable as String but the expression produces Int.
• Optional vs non-optional mismatch — assigning String? to a String variable.
• Subclass/superclass mismatch — assigning a parent class instance to a child class variable.
• Literal type inference confusion — 5 is Int, 5.0 is Double by default.

How to Fix It

1. Use explicit type conversion

let count: Int = 42
// ❌ Cannot assign Int to Double
let pi: Double = count

// ✅ Explicit conversion
let pi = Double(count)

2. Fix optional vs non-optional assignments

let optionalName: String? = "John"
// ❌ Cannot assign String? to String
let name: String = optionalName

// ✅ Either unwrap or use a default
let name = optionalName ?? "Guest"

3. Cast with as? or as! for Any types

let anyValue: Any = "Hello"
// ❌ Cannot assign Any to String
let text: String = anyValue

// ✅ Safe downcast
if let text = anyValue as? String {
    print(text)
}

4. Correct type annotations

// ❌ Literal "5" defaults to Int
let value: Float = 5

// ✅ Explicit Float literal
let value: Float = 5.0
// Or convert
let value = Float(5)