Typescript: Type '<R>(operator: Operator<T, R>) => Observable<T>' is not assignable to type '<R>(operator: Operator<T, R>) => Observable<R>'. Type 'Observable<T>' is not assignable to type 'Observable<R>'. Type 'T' is not assignable to type 'R'.

[thembela-daphula]

TypeScript Version: 3.4.0-dev.201xxxxx

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Code

// A *self-contained* demonstration of the problem follows...
// Test this by running `tsc` on the command-line, rather than through another build tool such as Gulp, Webpack, etc.

Expected behavior:

Actual behavior:

Playground Link:

Related Issues:

[dragomirtitian]

If you want to provide details about the issues you have upgrading, you can do so. But ranting that "everything is broken" is not really productive or actionable.

[thembela-daphula]

Most people are dealing with this issue. It has been there for quite sometime, rxjs^5.2.1 worked well with typescript 2.4 but since typescript upgraded in IDEs. It no longer works. Worse Ionic! To be honest I was starting to like typescript then this.

[fatcerberus]

Why would a function that returns Observable<T> be assignable to one that returns Observable<R>? They are different type parameters. Structural typing doesn't apply to generics because the compiler doesn't know which type(s) will be used.

[RyanCavanaugh]

Without some way to reproduce the issue or even see it, we're not going to be able to make any progress here. Please log a new issue with all the fields in the template filled in if appropriate.