Making OneOf feature not require strickNullCheck to be enabled.

[jimmymkude]

I played around with this, and I was eventually was able to get it work with ('strictNullChecks': false) by the changing the generated ts file to use a class to define the undefined oneof object instead of { oneofKind: undefined; }.

Using the docs example:

message OneofExample {
// Only one of (or none of) the fields can be set
oneof result {
int32 value = 1;
string error = 2;
}
}

interface OneofExample {
result: { oneofKind: "value"; value: number; }
| { oneofKind: "error"; error: string; }
| { oneofKind: undefined; };
}

This would change to:

class UndefinedOneOf {
oneofKind: undefined;
}

interface OneofExample {
result: { oneofKind: "value"; value: number; }
| { oneofKind: "error"; error: string; }
| UndefinedOneOf;
}

Now if we handle the undefined case first, it gives us the type guard to narrow down the type. For example, in the generated internalByteWrite function.

if (message.result instanceof UndefinedOneOf)
// Type guard above narrows down scope.
else if (message.result.oneofKind === "value")
// Knows the result type is not undefined.
Number.internalBinaryWrite(message.result.value, writer.tag(4, WireType.LengthDelimited).fork(), options).join();

What are your thoughts?

[timostamm]

Hey Jimmy, this is a valid workaround, but probably has some drawbacks around switch (x.oneofKind)?

It looks like strickNullChecks is enabled by default if you enable strict, which is greatly recommended. This was probably changed in one of the TypeScript versions in the past 1 or 2 years. I've updated the manual, thanks for raising this.

[jimmymkude]

Yes good point, I have verified that it doesn't work with switch statements since they don't provide the scope narrowing the if else provides.