Unions of References and TypedArrays

[willemneal]

The following doesn't compile

class Foo {}
function fooOrUint8Array(foo: Foo | Uint8Array): void {}

with the following error:

ERROR TS1005: 'null' expected.

 function fooOrUint8Array(foo: Foo | Uint8Array): void {}
                                    ^
 in assembly/main.ts(27,35)

Since Uint8Array has a class id, shouldn't this work?

Since WebAssembly.studio is down here is an example with near's fork:

https://studio.nearprotocol.com/?f=1cg9abhe2

[dcodeIO]

Wondering a bit, since union types are not supported. What am I missing?

[willemneal]

Instead of any, we can use a union type for the padding parameter:

/**
 * Takes a string and adds "padding" to the left.
 * If 'padding' is a string, then 'padding' is appended to the left side.
 * If 'padding' is a number, then that number of spaces is added to the left side.
 */
function padLeft(value: string, padding: string | number) {
    // ...
}

let indentedString = padLeft("Hello world", true); // errors during compilation

A union type describes a value that can be one of several types. We use the vertical bar (|) to separate each type, so number | string | boolean is the type of a value that can be a number, a string, or a boolean.

Were you thinking intersection types?

[DanielRX]

@willemneal that's typescript, not assemblyscript? Assembly script doesn't support unions as far as I've seen and tried?

[willemneal]

Ah yeah I had forgotten. Had seen a lot of | null like this: https://webassembly.studio/?f=yaok3afximh

And had forgotten. I managed to get around with generics like this: https://webassembly.studio/?f=nw6ffxidsvr

Perhaps we can add this to the discussion of #816 since with better type resolution this should be possible.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[trusktr]

Aren't issues like these good to keep open? I wonder if perhaps Google and other search engines might de-prioritize closed issues. Also searching for open issues (the default) won't show results. I may have then not created #1548 if I had found this one first. I thought I searched thoroughly before posting (guess I didn't!).

[dcodeIO]

To anyone coming here for a status update, a more detailed overview of the current status has meanwhile been added to the AS website. No updates on support for union types so far, though.