KK7 KK7 - 1 year ago 114
Swift Question

Swift recursive enums

I'm trying to learn more about recursive enums.

Here's my code:

enum Operation {
case Unary((Double) -> Double)
case Binary((Double, Double) -> Double)

indirect case Combined(Operation, Operation)

let x = 7.0
let y = 9.0
let z = x + y

let plus = Operation.Binary{$0 + $1}
let squareRoot = Operation.Unary{sqrt($0)}

let combined = Operation.Combined(plus, squareRoot)

switch combined {
case let .Unary(value): value(z)
case let .Binary(function): function(x, y)
case let .Combined(mix): mix(plus, squareRoot)

How can I perform
and then
operation one after another?

I keep getting this error:

Cannot call value of non-function type (Operation, Operation)

Answer Source

With .Unary and .Binary you are doing it right. You are retrieving the functions and executing them.

With .Combined however, you are retrieving a tuple of operations and using it as if it were a function. What you should do, is to retrieve the functions within the tuple and execute them.

Instead of your switch you could use a recursive function, like this:

func handleOperation(operation: Operation) {
    switch operation {
    case let .Unary(value): value(z)
    case let .Binary(function): function(x, y)
    case let .Combined(op1, op2): [op1, op2].map {handleOperation($0)}
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