min and max are defined in Swift: func max<T : Comparable>(x: T, y: T, rest: T…) -> T func min<T : Comparable>(x: T, y: T, rest: T…) -> T and used like so: let min = min(1, 2) let max = max(1, 2) See this great writeup on documented & undocumented built-in functions in Swift.
For a class with generic parameter T, you cannot do this because you have no type information for T since the JVM erases the type information. Therefore code like this cannot work: class Storage<T: Any> { val snapshot: Snapshot? = … fun retrieveSomething(): T? { return snapshot?.getValue(T::class.java) // ERROR “only classes can be used…” } … Read more
I also had this problem and I found a workaround for my case. In this article the author has the same problem https://www.iphonelife.com/blog/31369/swift-programming-101-generics-practical-guide So the problem seems to be, that the compiler needs to infer the type of T somehow. But it isn’t allowed to simply use generic< type >(params…). Normally, the compiler can look … Read more
Only one upper bound can be specified inside the angle brackets. Kotlin offers different syntax for generic constraints when there is more than one constraint: class Foo<T>(val t: T) where T : Bar, T : Baz { … } and for functions: fun <T> f(): Foo where T : Bar, T : Baz { … … Read more
Note: Generics were added to Go in version 1.18. You will find the answer here: http://golang.org/doc/faq#generics Why does Go not have generic types? Generics may well be added at some point. We don’t feel an urgency for them, although we understand some programmers do. Generics are convenient but they come at a cost in complexity … Read more
Create this inline fun: inline fun <reified T> Gson.fromJson(json: String) = fromJson<T>(json, object: TypeToken<T>() {}.type) and then you can call it in this way: val turns = Gson().fromJson<Turns>(pref.turns) // or val turns: Turns = Gson().fromJson(pref.turns) Previous Alternatives: ALTERNATIVE 1: val turnsType = object : TypeToken<List<Turns>>() {}.type val turns = Gson().fromJson<List<Turns>>(pref.turns, turnsType) You have to put … Read more
Generically, a covariant type parameter is one which is allowed to vary down as the class is subtyped (alternatively, vary with subtyping, hence the “co-” prefix). More concretely: trait List[+A] List[Int] is a subtype of List[AnyVal] because Int is a subtype of AnyVal. This means that you may provide an instance of List[Int] when a … Read more
List<out T> in Kotlin is equivalent to List<? extends T> in Java. List<in T> in Kotlin is equivalent to List<? super T> in Java For example in Kotlin you can do things like val value : List<Any> = listOf(1,2,3) //since List signature is List<out T> in Kotlin The reasoning is you can mark generic “out” … Read more
It may be helpful to think of the star projection as a way to represent not just any type, but some fixed type which you don’t know what is exactly. For example, the type MutableList<*> represents the list of something (you don’t know what exactly). So if you try to add something to this list, … Read more
You have a good point of view on this issue here: The Purpose of Scala’s Type System A Conversation with Martin Odersky, Part III by Bill Venners and Frank Sommers (May 18, 2009) Update (October2009): what follows below has actually been illustrated in this new article by Bill Venners: Abstract Type Members versus Generic Type … Read more