type Comparable = concept x, y (x < y) is bool

proc hoge(x,y: Comparable): bool = x>y echo(hoge(4, 2)) # Success echo(hoge('4', 2)) # Error

type Mul = concept x x * x

proc mul[T](arr: seq[T]): T = foldl(arr, a * b)

echo hoge @['1','2','3','4','5'] # Error echo hoge @[1,2,3,4,5] # Success

proc hoge(arr: Mul): Mul = foldl(arr, a * b) echo hoge @['1','2','3','4','5'] # 型検査でエラー(?)

type Addable = concept x x + x

Bowable = concept x bow(x) is string # プロシージャの制約 x.name is string # フィールドの制約. xはnameを持っている

# これでも動くわけだが、Personクラス(?)にgreetingメソッドを持つことを明示したい type OutputStream = concept var s s.greeting(string) type Person = object name: string proc greeting(self: Person, greeting: string) = echo greeting, self.name var p = Person(name:"hanako") p.greeting("good morning ") # ...うまく実装できなかった

# https://stackoverflow.com/questions/37550948/how-do-i-use-a-concept-in-nim type T = concept t t.a is string T0 = ref object a: string T1 = ref object a: string # ←コメントアウトするとコンパイルエラー q: string proc echoT(t: T) : void = echo "hello " & t.a echoT(T0(a: "T0")) echoT(T1(a: "T1", q: "q"))

type CanDance = concept x x.dance # `x`はdanceというprocedureを持っている # --- type Person = object Robot = object proc dance(p: Person) = echo "People can dance, but not Robots!" # --- let p = Person() let r = Robot() proc doBallet(dancer: CanDance) = # `dancer` can be anything that `CanDance` dance(dancer) doBallet(p) # pはdanceメソッド(?)持っているので「People can dance, but not Robots!」と出力される # doBallet(r) # rはdanceメソッド(?)を持っていないのでコンパイルエラーになる

# https://gist.github.com/honewatson/583135c1b191119a3b3be3fdbfe8607b import strutils, strformat type Dispatch = enum Reveal IKind = enum Human, NonHuman ObIkind = ref object of RootObj kind: IKind Person = object of ObIkind name: string Robot = object of ObIkind name: int Place = object of ObIkind description: string Data = concept x toString(x) x.kind is IKind # We can use a generic proc as a starting point to satisfy `Data` concept proc `toString` proc toString[T](data: T): string = return fmt"{data.name} is a {data.kind}" # We can provide a specific `toString` proc for place which does not have a property of `name` proc toString(place: Place): string = return fmt"{place.description} is a {place.kind}" var d1 = Person(kind: Human, name: "Jim") d2 = Place(kind: NonHuman, description: "Hill") d3 = Robot(kind: NonHuman, name: 738191) # Here we create a proc actions which has takes concept of type Data as one of the parameters # The concept of type Data is essentially a kind of restricted generic # This should work for both the C and JS Backends proc actions(dispatch: Dispatch, data: Data): string = case dispatch: of Reveal: data.toString() echo actions(Reveal, d1) # Jim is a Human echo actions(Reveal, d2) # Hill is a NonHuman echo actions(Reveal, d3) # 738191 is a NonHuman

enum Dispatch { Reveral } enum IKind { Human, NonHuman } class ObIkind { kind: IKind; } class Person { constructor(public kind: IKind, public name: string) {} } class Robot extends ObIkind { constructor(public kind: IKind, public name: number) { super(); } } class Place extends ObIkind implements Data { constructor(public kind: IKind, public description: string) { super(); } toString() { return `${this.description} is a ${this.kind}`; } } interface Data { toString: (x) => string; kind: IKind; } const d1 = new Person(IKind.Human, 'Jim'); const d2 = new Place(IKind.NonHuman, 'Hill'); const d3 = new Robot(IKind.NonHuman, 738191); const actions = (dispatch: Dispatch, data: Data) => { switch (dispatch) { case Dispatch.Reveral: data.toString(); default: break; } };

type Value = concept v v.value is bool # bool型のプロパティ`value`を持っている MinValue = concept v v is Value v.minVal is bool # bool型を返すminValメソッドを持っている MaxValue = concept v v is Value v.maxVal is bool type BoolParam = ref object value: bool proc set(self: Value, v: bool): bool = # following block only compiled when expr is true when self is MinValue: if v < self.minVal: return false when self is MaxValue: if v > self.maxVal: return false self.value = v return true let b = BoolParam(value: false) echo b.set(true) echo b.value

proc energy[PhysicalObject](o: PhysicalObject): float = 0.5 * o.mass * o.speed * o.speed # プロパティとして,mass,speedを持つ type SimpleObject = object mass: float speed: float # メソッドとしてmass,speedを持つ type ComposedObject = object proc mass(self: ComposedObject): float = 42 proc speed(self: ComposedObject): float = 42 let simple = SimpleObject(mass: 1.0, speed: 5.0) echo simple.energy # 0.5 * 1.0 * 5.0 * 5.0 = 12.5 let composed = ComposedObject() echo composed.energy # 0.5 * 42 * 42 * 42 = 37044.0

type Comparable = concept x, y (x < y) is bool # xとyは比較できる # 利用例 proc hoge(x,y: Comparable): int = return y echo hoge(4, 2) echo hoge('4', 2) # コンパイルエラー!!