Prototype of Ownership/Borrowing System for D

[Ola Fosheim Grøstad]

On Friday, 22 November 2019 at 06:43:01 UTC, mipri wrote:
> I've never used TypeScript, but Kotlin's handling of nullable 
> types
> is nice to the point I'd rather use the billion dollar mistake 
> than
> an optional type.

Kotlin has type inference, but TypeScripts has to be able to 
describe existing JavaScript data-models, so that it can provide 
stricter typing from existing JavaScript libraries. As a 
consequence TypeScript has to allow "crazy" mixing of types. Thus 
a function can have  parameters and a return type that is a union 
of "incompatible" types. To make this work it fully embraces 
flow-typing, that is: the type is determined by all possible 
execution paths within a function. Thus TypeScript has many 
features to deal with "undefined" (unitialized or non-existing 
variable) and "null" (missing object) as you have to deal with 
those from JavaScript code. And of course, this becomes a very 
valuable tool when transitioning code to TypeScript from 
JavaScript, or from a prototype to production code.

The verification language Whiley is following the same core 
flow-typing principle, but since the type system of Whiley 
employs a SMT engine it has more potential than TypeScript IMO. 
See page 8 in 
http://whiley.org/download/GettingStartedWithWhiley.pdf . (I 
don't think it is production ready, but interesting nevertheless).