Incorrect type inference in class implementation of interface with method Accepting partial type about typescript HOT 4 CLOSED

This is working as intended, methods are bivariant. See this FAQ entry: Why Method Bivariance?

You can use the property syntax to get covariant behavior: mapToVoid: (m: Partial<M>) => void

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not sure I'll classify it as working as intended since it is clearly not working in the runtime and caused a bug in my project

"Working as intended" = working as the TypeScript compiler devs intend. The behavior of TypeScript here is intentional, even if it leads to runtime errors. The type system is intentionally not fully sound: to quote the design goals, TS is designed to "strike a balance between correctness and productivity"; in this case, enforcing strictMethodTypes would be a major roadblock in practice for almost any code people would want to write so it isn't done.

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@MartinJohns Thank you, I read the article even though I don't 100% understand but I get that it's kind of a limitation, not sure I'll classify it as working as intended since it is clearly not working in the runtime and caused a bug in my project

but since we have a way forward I think I'll close the ticket

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@fatcerberus I understand exactly why isn't it done, I'm happy too that there's way to solve my problem and move forward so I closed the issue, I know it's what the ts devs are aware of but to me it sounds more like a limitation or known issue where they just accepted that it's not worth fixing (if there was a magic way to fix it without any negative impact I think they would do it), working as intended for me is something is working based on your design but this is just my personal feeling

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