`Result value must be used` check

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
25/100
Issue type
Feature
Clarity
Needs clarification
Activity status
Stale
Tech stack
typescript
Domain
compilers

Research direction

This issue is a design discussion about expressing a “must use the result” check in the TypeScript compiler, with ImmutableJS and Rust’s #[must_use] annotation as examples. No implementation files, tests, or compiler entry points are identified; first clarify the language design and expected behavior before locating the relevant checker and test areas.

Written by the indexing model from the issue text.

Description

Awaiting More Feedback Suggestion

Hello.

Quite often while working with ImmutableJS data structures and other immutable libraries people forget that values are immutable:

They can accidentally write:

obj.set('name', 'newName');

Instead of:

let newObj = obj.set('name', 'newName');

These errors are hard to discover and they are very annoying. I think that this problem can't be solved by tslint, so I propose to add some sort of "you must use the result" check into the compiler. But right now I have no idea how I want it to be expressed in the language, so I create this issue mainly to start a discussion.

Rust lang, for example, solves a similar problem with #[must_use] annotation. This is not exact what we want, but it's a good example and shows that the problem is quite common.

Dominant language
Go
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Forks
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Avg merge
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Merged PRs (30d)
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