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@ColinEberhardt
Created March 20, 2015 08:14
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Pipe forward operator and curried free functions = fluent interface
// meet Stringy - a simple string type with a fluent interface
struct Stringy {
let content: String
init(_ content: String) {
self.content = content
}
func append(appendage: Stringy) -> Stringy {
return Stringy(self.content + " " + appendage.content)
}
func printMe() {
println(content)
}
}
//////////////////////////////////////////////////////////////////////
// Stringy in action ...
var greeting = Stringy("Hi")
greeting.append(Stringy("how"))
.append(Stringy("are"))
.append(Stringy("you?"))
.printMe() // => "Hi how are you?"
// A lovely fluent interface!
//////////////////////////////////////////////////////////////////////
// Now what append and printMe were 'free functions'?
func appendFreeFunction(a: Stringy, b: Stringy) -> Stringy {
return Stringy(a.content + " " + b.content)
}
func printMe(a: Stringy) {
a.printMe()
}
// Stringy with free functions in action ...
printMe(
appendFreeFunction(
appendFreeFunction(
appendFreeFunction(greeting, Stringy("how")), Stringy("are")), Stringy("you?")))
// => "Hi how are you?"
// Yuck - we no longer have the fluent interface, with a real mess of brackets
//////////////////////////////////////////////////////////////////////
// Pipe forward
// modify the free functions, turnign them into curried functions
func appendCurriedFreeFunction(a: Stringy)(b: Stringy) -> Stringy {
return Stringy(b.content + " " + a.content)
}
// and define a pipe forward operator
infix operator |> { associativity left }
func |><X> (stringy: Stringy, transform: Stringy -> X) -> X {
return transform(stringy)
}
// we now have free functions AND a fluent interface
greeting
|> appendCurriedFreeFunction(Stringy("how"))
|> appendCurriedFreeFunction(Stringy("are"))
|> appendCurriedFreeFunction(Stringy("you?"))
|> printMe // => "Hi how are you?"
@chrishulbert
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Mind blown. This is epic. Thanks for taking it step-by-step!

@schickling
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👍

@andrelevi
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Thank you for this!

@LawrenceHan
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HOLY S**T!

@lforme
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lforme commented Apr 12, 2016

👍

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