A
arktype•4w ago
Untlsn

Match `.in` with loose type

In docs there is example 
type Data =
  | {
    id:       1
    oneValue: number
  }
  | {
    id:       2
    twoValue: string
  };
const discriminateValue = type.match
// .in allows you to specify the input TypeScript allows for your matcher
  .in<Data>()
// .at allows you to specify a key at which your input will be matched
  .at('id')
  .match({
    1:       (o) => `${o.oneValue}!`,
    2:       (o) => o.twoValue.length,
    default: 'assert',
  });
type Data =
  | {
    id:       1
    oneValue: number
  }
  | {
    id:       2
    twoValue: string
  };
const discriminateValue = type.match
// .in allows you to specify the input TypeScript allows for your matcher
  .in<Data>()
// .at allows you to specify a key at which your input will be matched
  .at('id')
  .match({
    1:       (o) => `${o.oneValue}!`,
    2:       (o) => o.twoValue.length,
    default: 'assert',
  });
Its work good because match know how rest of the type will look like, so we have acess to oneValue or twoValue But when i change it to: 
type Data = {
  id:    '1' | '2'
  value: number
};
const discriminateValue = type.match
// .in allows you to specify the input TypeScript allows for your matcher
  .in<Data>()
// .at allows you to specify a key at which your input will be matched
  .at('id')
  .match({
    1:       (o) => `${o.value}!`,
    2:       (o) => o.value.length,
    default: 'assert',
  });
type Data = {
  id:    '1' | '2'
  value: number
};
const discriminateValue = type.match
// .in allows you to specify the input TypeScript allows for your matcher
  .in<Data>()
// .at allows you to specify a key at which your input will be matched
  .at('id')
  .match({
    1:       (o) => `${o.value}!`,
    2:       (o) => o.value.length,
    default: 'assert',
  });
Typescript say that only id exist Is this an issue, or intentional? Probably second one, because i need to make 
typeof o & Omit<Data, keyof typeof o>
typeof o & Omit<Data, keyof typeof o>
to get anything else then never from typescript Then what should I use as alternative?
2 Replies
ssalbdivad
ssalbdivad•4w ago
Hey thanks for writing this up. While generally it is helpful to match against a discriminated union like the on in your original example, the current behavior of this example is definitely an inference bug in ArkType. We're making some other improvements to matching for 2.2 , would you be willing to create a GitHub issue for this so we can track it?
ssalbdivad
ssalbdivad•4w ago
Created an issue here: https://github.com/arktypeio/arktype/issues/1373
GitHub
match .at with collaposed union at prop does not work · Issue #13...
This is a confirmed issue copied from a Discord question. In docs there is example: type Data = | { id: 1 oneValue: number } | { id: 2 twoValue: string }; const discriminateValue = type.match // .i...

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