generics

问题 In Option we have def getOrElse[B >: A](default: => B): B = this match { case None => default case Some(a) => a } def orElse[B >: A](obj: => Option[B]): Option[B] = this match { case None => obj case _ => this } In Either we have: def flatMap[EE >: E, B](f: A => Either[EE, B]): Either[EE, B] I understand what is going and why, a rather extended example could be this OrElse( { Option[B]}).map{....} If B is such that A :> B, then if Some(a) you get Some(a).map(f:B => ???) then Kaboom generally

问题 Let's have these classes: class A { fun foo(): A = this } class B: A() { fun bar() { ... } } Now I would like Kotlin to detect when I call foo on B , and give me the result typed as B . So that I can write: B().foo().bar() With kotlin 1.4.20, this is not possible - it would need an explicit cast to B after foo() . Perhaps it could be handled by the compiler, if it clearly sees that the function returns this . Or maybe we could hint it explicitly... class A { fun <Self> foo(): Self = this } I

问题 Let's have these classes: class A { fun foo(): A = this } class B: A() { fun bar() { ... } } Now I would like Kotlin to detect when I call foo on B , and give me the result typed as B . So that I can write: B().foo().bar() With kotlin 1.4.20, this is not possible - it would need an explicit cast to B after foo() . Perhaps it could be handled by the compiler, if it clearly sees that the function returns this . Or maybe we could hint it explicitly... class A { fun <Self> foo(): Self = this } I

问题 I am very new to TypeScript. My TypeScript version is 3.7.5. IMHO, it should be very easy, but I don't know why it does not work. function add<T> (a:T, b:T):T { return a + b ; } console.log(add (5, 6)); I get the error: Operator '+' cannot be applied to types 'T' and 'T'. I used this one also: function add<T extends string | number > (a:T, b:T):T The same error is there. If I can not use + for this generic, why should I use generics ? 回答1: Generics are not the right approach here. You cannot

问题 I cannot make compile Spock stub for generic class. The signature of constructor is following: SomeClass(SerSup<Cap> capSup, String foo, String bar); I need to stub the first argument. The following are my failed attempts. First try: def someClass = new SomeClass(Stub(SerSup<Cap>), "foo", "bar") Error: Groovyc: unexpected token: > Status bar: ',' or ')' expected Another try: def someClass = new someClass(Stub(Cup) as SerSup<Cup>, "foo" ,"bar") groovy.lang.MissingMethodException: No signature

问题 I cannot make compile Spock stub for generic class. The signature of constructor is following: SomeClass(SerSup<Cap> capSup, String foo, String bar); I need to stub the first argument. The following are my failed attempts. First try: def someClass = new SomeClass(Stub(SerSup<Cap>), "foo", "bar") Error: Groovyc: unexpected token: > Status bar: ',' or ')' expected Another try: def someClass = new someClass(Stub(Cup) as SerSup<Cup>, "foo" ,"bar") groovy.lang.MissingMethodException: No signature

问题 I cannot make compile Spock stub for generic class. The signature of constructor is following: SomeClass(SerSup<Cap> capSup, String foo, String bar); I need to stub the first argument. The following are my failed attempts. First try: def someClass = new SomeClass(Stub(SerSup<Cap>), "foo", "bar") Error: Groovyc: unexpected token: > Status bar: ',' or ')' expected Another try: def someClass = new someClass(Stub(Cup) as SerSup<Cup>, "foo" ,"bar") groovy.lang.MissingMethodException: No signature

问题 I want to write a type constructor for a function which receives a type S and a function from S to another type then applies that function on the S and returns the result: // This works but it's tied to the implementation function dig<S, R>(s: S, fn: (s: S) => R): R { return fn(s); } // This works as separate type constructor but I have to specify `R` type Dig<S, R> = (s: S, fn: (s: S) => R) => R; // Generic type 'Dig' requires 2 type argument(s). const d: Dig<string> = (s, fn) => fn(s); So

问题 I want to write a type constructor for a function which receives a type S and a function from S to another type then applies that function on the S and returns the result: // This works but it's tied to the implementation function dig<S, R>(s: S, fn: (s: S) => R): R { return fn(s); } // This works as separate type constructor but I have to specify `R` type Dig<S, R> = (s: S, fn: (s: S) => R) => R; // Generic type 'Dig' requires 2 type argument(s). const d: Dig<string> = (s, fn) => fn(s); So

问题 I have the following example Object: let foo: Foo = { 'key1': { default: 'foo', fn: (val:string) => val }, 'key2': { default: 42, fn: (val:number) => val }, // this should throw an error, because type of default and fn don't match 'key3': { default: true, fn: (val:string) => val } } The Interface should look something like this: interface Foo { [key: string]: { default: T, fn: (val:T) => any } } This of course doesn't work, because there's no T defined. So I thought about doing this: