CODEWITHSUNDEEP
swift
jonesjones
jonesjones

Reputation: 497

Is it possible to add function definitions programmatically in swift

I'm creating a struct that holds 3 float values,

struct Col {
  var r: Float
  var g: Float
  var b: Float
}

and I'd like to add a bunch of function definitions that are equivalent to the built in math functions, but that operate piecewise on the members of my struct

I can do it by hand, eg

func pow(a: Col, b: Col) -> Col {
  return Col(r: pow(a.r, b.r), g: pow(a.g, b.g), b: pow(a.b, b.b))
}

but this is tedious and error prone.

What I'd like to do is create a function to turn the original math function into my Col version, so that I could call it like this:

defineColVersion(pow, noArgs: 2)

and it defines the new version, without overwriting the built in function that operates on Doubles

Is there any way to do this in Swift?

Thanks

Upvotes: 3

Views: 217

Answers (3)

Kametrixom
Kametrixom

Reputation: 14983

I actually think this is exactly what you want:

func toCol(f: (Float, Float) -> Float) -> (Col, Col) -> Col {
    return { a, b in
        Col(r: f(a.r, b.r), g: f(a.g, b.g), b: f(a.b, b.b))
    }
}

func toCol(f: Float -> Float) -> Col -> Col {
    return { c in
        Col(r: f(c.r), g: f(c.g), b: f(c.b))
    }
}

let pow = toCol(Darwin.pow)
let sin = toCol(Darwin.sin)
let log = toCol(Darwin.log)

let a = Col(r: 0.4, g: 0.2, b: 0.7)
let b = Col(r: 0.3, g: 0.9, b: 0.3)

pow(a, b)
sin(a)
log(b)

The two overloaded functions toCol take a unary/binary function on Floats and returns a new function which does the same on your Col type. With those two, you can easily create a pow function for your Col type.

Upvotes: 5

johnpatrickmorgan
johnpatrickmorgan

Reputation: 2372

func init(first: Col, second: Col, function: (Float, Float) -> Float ) {
    newR = function(first.r,second.r)
    newG = function(first.g,second.g)
    newB = function(first.b,second.b)
    return self.init(r:newR,g:newG,b:newB)
}

I'm not in a position to compile this so it probably has some errors but hopefully it will be useful. You would use it like so:

first = Col(r:1,g:2,b:3)
second = Col(r:1,g:2,b:3)
combined = Col(first:first,second:second) { pow($0,$1) }

Upvotes: 0

Clashsoft
Clashsoft

Reputation: 11882

It is not possible to programmatically define new functions in a static language like Swift. What you can do, however, is to make a higher-kinded function:

func init(a: Col, b: Col, function: (Float, Float) -> Float) -> Col {
    return self.init(r: function(a.r, b.r), g: function(a.g, b.g), b: function(a.b, b.b))
}

Col(Col(1, 2, 3), Col(3, 4, 5)) { $0 * $1 }
Col(Col(1, 2, 3), Col(3, 4, 5)) { pow($0, $1) }

Upvotes: 3

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