In AssemblyScript, I'm trying to define an instance method in a base class that will return the instance it's called on. I can do this, but the return type does not seem to be resolved correctly.
Here's an example. I try this, which works in TypeScript:
class X {
doSomething(): this {
return this;
}
}
class Y extends X {
doSomethingElse(): string {
return "You made it!";
}
}
log(new Y().doSomething().doSomethingElse());
In AssemblyScript, it seems that the type of .doSomething() is determined to be X rather than Y.
ERROR TS2339: Property 'doSomethingElse' does not exist on type '__main__/X'.
:
23 │ log(new Y().doSomething().doSomethingElse());
│ ~~~~~~~~~~~~~~~
└─ in __main__.ts(23,27)
I am new to both TypeScript and AssemblyScript, and am wondering if maybe there are differences in how these languages resolve this - if maybe I just need to use something besides this - or if this might be some sort of bug or feature that I could/should request. I'm also sorry if there is an answer to this available - I've been trying to construct a good search for it, and it hasn't turned up anything useful. I also tried to see what might be happening by looking through the AssemblyScript codebase, but after initial attempts, I think that will take me a very long time, and so I wanted to ask for the benefit of anyone who could happen to be in my situation. I'm using the assemblyscript npm package at version 0.27.30, which is currently only one patch version behind the latest version.
My question is - is there a way to declare doSomething, from my example, so that AssemblyScript knows it returns the same type as the instance it is called on? Is there a difference in how AssemblyScript handles references to this, that could help explain this?
Your code is valid TypeScript, but indeed this seems to be either a bug or a deficiency in AssemblyScript.
I've created a GitHub issue to report the problem: https://github.com/AssemblyScript/assemblyscript/issues/2904