lmiguelvargasf lmiguelvargasf - 1 year ago 71
Swift Question

How can I return a function that depends on two functions?

I have the following function:

private func getFunctionToPlot() -> ((Double) -> Double) {
var function: (Double) -> Double = sin + cos
return function


I would like to return a function that takes a double and returns a double, but this functions should be something as
sin + cos
. Both sin and cos independently take a double and return a double, but how can I return something as
sin($0) + cos($0)

Answer Source

Your question is a little broad, but the line you claim doesn't compile does compile; there's nothing wrong with what you're doing. The only problem is that your code is incomplete. Here is a test example that is complete:

private func getFunctionToPlot() -> ((Double) -> Double) {
    var function: (Double) -> Double
    function = {_ in return 2.0}
    return function

EDIT As for your revised question, here's a test example of the sort of thing you now seem to be trying to do:

func sin(_ d:Double) -> Double {return 1}
func cos(_ d:Double) -> Double {return 1}
private func getFunctionToPlot() -> ((Double) -> Double) {
    let f1: (Double) -> Double = sin
    let f2: (Double) -> Double = cos
    return {f1(f2($0))} // or maybe f1($0) + f2($0)
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