[OT] Some neat ideas from the Kotlin language

[Jacob Carlborg via Digitalmars-d]

On 2016-02-19 00:33, Yuxuan Shui wrote:
> Just come across Kotlin today, and found some interesting ideas skimming
> through its tutorial:
>
> 1) Null check
>
> Kotlin has Optional types, suffixed with a '?'. Like 'Int?', same as in
> Swift. But instead of explicitly unwrapping them (e.g. var! in Swift, or
> var.unwrap() in Rust), Kotlin let you do this:
>
>
>      var: Int?
>      if (var != null)
>          //You can use var here
>
>
> Skipping the null check will get you compile time error.
>
> You can even do this:
>
>      if (var == null) return;
>      //You can use var from now on

I think the same applies to Swift. But I think you're supposed to use it 
like this:

if let a = var {
   // a is no unwrapped
}

I like the way it's used in Scala:

val a = Option(value)
val b = a.map(e => e /* do something with the unrapped e).getOrElse(/* 
use a default value here */)

The Option type in Scala acts like a zero or one element collection. The 
Scala way can be implemented in D as well without any language support.

> 2) Smart cast
>
> This is a similar to previous one, instead of:
>
>      var1: Object;
>      var2 = cast(String)var1;
>
> You do this:
>
>      if (var1 is String)
>          //You can use var1 as a String here

It's similar how it works in D, for Objects:

class Foo {}
Object foo = new Foo;

if (auto o = cast(Foo) foo)
     // use o as Foo here

When casting to a subclass it will return null reference if the cast fails.

-- 
/Jacob Carlborg