Why let x as Float case is not matching in a switch on a Any variable?

Question

I have an enum for tagged values (this is from a toy Scheme interpreter project), like this:

enum Value {
  case int(Int)
  case float(Float)
  case bool(Bool)
  ...
}

I wrote an initializer for it:

init?(value:Any) {
  switch v {
    case let v as Int: self = .int(v)
    case let v as Float: self = .float(v)
    case let v as Bool: self = .bool(v)
    ...
    default: return nil
  }
}

With that, calling Value(3) returns an (optional) Value.int(3), as expected. Bool's and the other types work too.

But Value(0.1) hits the default case and returns nil.

(Edited for correctness and recommended style. Thank you everyone for pointing those issues out.)

Answer 1

The default inferred type for floating point constants is Double, not Float. It's defined by the swift standard library here: https://developer.apple.com/reference/swift/floatliteraltype using the compiler-known FloatLiteralType typealias.

Answer 2

The documentation of type inference says:

Swift always chooses Double (rather than Float) when inferring the type of floating-point numbers.

If you want to use Float, you must explicitly cast the literal:

enum Value {
    case Int(Int)
    case Float(Float)
    case Bool(Bool)
    case Double(Double)
    init?(v:Any) {
        switch v {
        case let v as Int: self = .Int(v)
        case let v as Float: self = .Float(v)
        case let v as Bool: self = .Bool(v)
        case let v as Double: self = .Double(v)
        default: return nil
        }
    }
}


Value(v: 0.1) //Infer Double > Result: Double(0.10000000000000001)
Value(v: Float(0.0002)) //Specify Float > Result: Float(0.000199999995)