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56 lines
2.3 KiB
TypeScript
56 lines
2.3 KiB
TypeScript
import type {BuildTuple} from './internal/index.d.ts';
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import type {Subtract} from './subtract.d.ts';
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/**
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Generate a union of numbers.
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The numbers are created from the given `Start` (inclusive) parameter to the given `End` (exclusive) parameter.
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You skip over numbers using the `Step` parameter (defaults to `1`). For example, `IntRange<0, 10, 2>` will create a union of `0 | 2 | 4 | 6 | 8`.
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Note: `Start` or `End` must be non-negative and smaller than `1000`.
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Use-cases:
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1. This can be used to define a set of valid input/output values. for example:
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```
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type Age = IntRange<0, 120>;
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type FontSize = IntRange<10, 20>;
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type EvenNumber = IntRange<0, 11, 2>; //=> 0 | 2 | 4 | 6 | 8 | 10
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```
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2. This can be used to define random numbers in a range. For example, `type RandomNumber = IntRange<0, 100>;`
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@example
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```
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import type {IntRange} from 'type-fest';
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// Create union type `0 | 1 | ... | 9`
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type ZeroToNine = IntRange<0, 10>;
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// Create union type `100 | 200 | 300 | ... | 900`
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type Hundreds = IntRange<100, 901, 100>;
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```
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@see IntClosedRange
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*/
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export type IntRange<Start extends number, End extends number, Step extends number = 1> = PrivateIntRange<Start, End, Step>;
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/**
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The actual implementation of `IntRange`. It's private because it has some arguments that don't need to be exposed.
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*/
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type PrivateIntRange<
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Start extends number,
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End extends number,
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Step extends number,
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Gap extends number = Subtract<Step, 1>, // The gap between each number, gap = step - 1
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List extends unknown[] = BuildTuple<Start, never>, // The final `List` is `[...StartLengthTuple, ...[number, ...GapLengthTuple], ...[number, ...GapLengthTuple], ... ...]`, so can initialize the `List` with `[...StartLengthTuple]`
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EndLengthTuple extends unknown[] = BuildTuple<End>,
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> = Gap extends 0 ?
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// Handle the case that without `Step`
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List['length'] extends End // The result of "List[length] === End"
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? Exclude<List[number], never> // All unused elements are `never`, so exclude them
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: PrivateIntRange<Start, End, Step, Gap, [...List, List['length'] ]>
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// Handle the case that with `Step`
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: List extends [...(infer U), ...EndLengthTuple] // The result of "List[length] >= End", because the `...BuildTuple<Gap, never>` maybe make `List` too long.
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? Exclude<List[number], never>
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: PrivateIntRange<Start, End, Step, Gap, [...List, List['length'], ...BuildTuple<Gap, never>]>;
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