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Add Omit as a known interface #30455

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Add Omit as a known interface#30455
#30552
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DanielRosenwasser
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Breaking ChangeWould introduce errors in existing codeCommittedThe team has roadmapped this issueFixedA PR has been merged for this issueIn DiscussionNot yet reached consensusSuggestionAn idea for TypeScript
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TypeScript 3.5.0

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@basarat
Basarat Ali Syed (basarat)
opened on Mar 18, 2019

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Omit

Suggestion

Add the following type to lib.d.ts:

type Omit<ObjectType, KeysType extends keyof ObjectType> = Pick<ObjectType, Exclude<keyof ObjectType, KeysType>>;

More

Origin : #12215 (comment)

From : https://github.com/sindresorhus/type-fest/blob/0226ef2092ee2b07a8714c832d106da659877a8f/index.d.ts#L75 Please open new issues on TypeScript about making it built-in.. I searched but couldn't find an issue, so here it is 🌹

Checklist

My suggestion meets these guidelines:

  • This wouldn't be a breaking change in existing TypeScript/JavaScript code
  • This wouldn't change the runtime behavior of existing JavaScript code
  • This could be implemented without emitting different JS based on the types of the expressions
  • This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
  • This feature would agree with the rest of TypeScript's Design Goals.

Activity

  1. j-oliveras commented on Mar 18, 2019

    @j-oliveras
    Jordi Oliveras Rovira (j-oliveras)
    on Mar 18, 2019
    Contributor

    Duplicate of #19569?

  2. weswigham commented on Mar 18, 2019

    @weswigham
    Wesley Wigham (weswigham)
    on Mar 18, 2019
    Member

    Not really? That was back when there was only a hairy mapped-type based definition of Omit which we didn't particularly like, so didn't want to add.

  3. nmain commented on Mar 19, 2019

    @nmain
    Nicholai Main (nmain)
    on Mar 19, 2019

    Eventually that issue was closed after conditional types were added. Anders Hejlsberg (@ahejlsberg) made #21847 and said:

    We did not include the Omit<T, K> type because it is trivially written as Pick<T, Exclude<keyof T, K>>

  4. dragomirtitian commented on Mar 19, 2019

    @dragomirtitian
    Titian Cernicova-Dragomir (dragomirtitian)
    on Mar 19, 2019
    Contributor

    Nicholai Main (@nmain) My 2¢, trivial for some magic for others, I would argue all build-in mapped and conditional types are trivial to write but that does not make them any less useful. Having a common set of types makes code easier to understand across projects. Omit is also simpler to understand for newer typescript devs and they don't have to do conditional type math when looking at a definition, they just care about the behavior of the type.

  5. sindresorhus commented on Mar 20, 2019

    @sindresorhus
    Sindre Sorhus (sindresorhus)
    on Mar 20, 2019

    I personally use Omit much more often than the other built-in helper types.

  6. jeremiergz commented on Mar 21, 2019

    @jeremiergz
    Jeremie Rodriguez (jeremiergz)
    on Mar 21, 2019

    Totally agree, I end up declaring that Omit type in almost every project.
    It's like Record<string, string> could be written { [k: string]: string}. I prefer the Record helper, same feeling about this one.

  7. SleeplessByte commented on Mar 21, 2019

    @SleeplessByte
    Derk-Jan Karrenbeld (SleeplessByte)
    on Mar 21, 2019

    I've used Omit in every single project and every single time I have to look it up, because Pick<T, Exclude<keyof T, K>> isn't trivial to recall; if many people use it in every project, it make sense to make it part of lib.d.ts right?

    It's like Record<string, string> could be written { [k: string]: string}. I prefer the Record helper, same feeling about this one.

    That's not the same; and it's not even close.

  8. jeremiergz commented on Mar 21, 2019

    @jeremiergz
    Jeremie Rodriguez (jeremiergz)
    on Mar 21, 2019

    That's not the same; and it's not even close.

    How so? Isn't it better to explain your train of thought when you say someone's wrong?...

  9. SleeplessByte commented on Mar 21, 2019

    @SleeplessByte
    Derk-Jan Karrenbeld (SleeplessByte)
    on Mar 21, 2019

    That's not the same; and it's not even close.

    How so? Isn't it better to explain your train of thought when you say someone's wrong?...

    Sorry, you're right -- and my thoughts were wrong anyway. I would even say that omit is far more difficult than record!

    What I should have said is that it's better to compare Record<keyof K, string> to { [P in K]: string }.

  10. fabiospampinato commented on Mar 22, 2019

    @fabiospampinato
    Fabio Spampinato (fabiospampinato)
    on Mar 22, 2019

    The docs' reasoning about this is:

    We did not include the Omit<T, K> type because it is trivially written as Pick<T, Exclude<keyof T, K>>

    I'm not so sure about the triviality of it, especially for new TS devs, but IMHO this isn't a good reason for not including Omit, to me it feels like saying that if I have this code:

    return collection.map ( item => item.foo () );

    I don't really need map because it's trivial to do the same with forEach:

    const result = [];
collection.forEach ( item => result.push ( item.foo () ) );
return result;

    I mean yeah, it's trivial, but am I supposed to write such ugly code every time or am I supposed to redefine map every time?

  11. Ryan Cavanaugh (RyanCavanaugh)
    added
    SuggestionAn idea for TypeScript
    In DiscussionNot yet reached consensus
    on Mar 25, 2019
  12. Daniel Rosenwasser (DanielRosenwasser)
    added
    CommittedThe team has roadmapped this issue
    on Apr 4, 2019
  13. Daniel Rosenwasser (DanielRosenwasser)
    added this to the TypeScript 3.5.0 milestone on Apr 4, 2019
  14. Daniel Rosenwasser (DanielRosenwasser)
    self-assigned this
    on Apr 4, 2019
  15. Daniel Rosenwasser (DanielRosenwasser)
    closed this as completedin #30552on Apr 4, 2019
  16. Daniel Rosenwasser (DanielRosenwasser)
    added
    FixedA PR has been merged for this issue
    on Apr 4, 2019

  17. DanielRosenwasser commented on Apr 4, 2019

    @DanielRosenwasser
    Daniel Rosenwasser (DanielRosenwasser)
    on Apr 4, 2019
    Member

    This is now 3.5-bound! 🚀

    You can try it out with our next nightly release.

  18. Daniel Rosenwasser (DanielRosenwasser)
    added
    Breaking ChangeWould introduce errors in existing code
    on Apr 5, 2019

  19. leidegre commented on Apr 7, 2019

    @leidegre
    John Leidegren (leidegre)
    on Apr 7, 2019

    For those curious how the Omit type is used, you can find that information here.

  20. NoelAbrahams commented on Apr 9, 2019

    @NoelAbrahams
    Noel Abrahams (NoelAbrahams)
    on Apr 9, 2019

    The naming of this is rather unfortunate. I mean to say, what exactly is the difference between the words "Omit" and "Exclude"? They are essentially synonyms with a minor nuance.

    The definition we have used is ExcludeProperty.

    /**
 * Exclude from T those types that are assignable to U
 */
type Exclude<T, U> = T extends U ? never : T;

/**
 * From T remove the properties K
 * E.g. ExcludeProperty<{ a: number, b: string }, 'b'> => { a: number }
 */
type ExcludeProperty<T, K extends keyof T> = Pick<T, Exclude<StringKeyOf<T>, K>>;

  21. sindresorhus commented on Apr 10, 2019

    @sindresorhus
    Sindre Sorhus (sindresorhus)
    on Apr 10, 2019

    For everyone watching this issue, note that the Omit type that was added is not the strict one suggested here. See: #30825.

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