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feat(array): narrow return type for first and last #140

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feat(array): narrow return type for first and last #140

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6 changes: 4 additions & 2 deletions src/array/first.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -11,9 +11,11 @@
* // 0
* ```
*/
export function first<T>(array: readonly T[]): T | undefined
export function first(array: readonly []): undefined
export function first<T>(array: readonly T[]): T
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Can't assume the length of the array type is not zero here, so return type has to be T | undefined. Or is your goal to align this with arr[0]-style access?

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@MarlonPassos-git MarlonPassos-git Jul 28, 2024 •
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It's the same case as #139 (comment)

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Agreed, invalid for similar reasons. Suggest closing.


export function first<T, U>(array: readonly T[], defaultValue: U): T | U
export function first<U>(array: readonly [], defaultValue: U): U
export function first<T, U>(array: readonly T[], defaultValue: U): T

export function first(array: readonly unknown[], defaultValue?: unknown) {
return array?.length > 0 ? array[0] : defaultValue
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6 changes: 4 additions & 2 deletions src/array/last.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -11,9 +11,11 @@
* // 0
* ```
*/
export function last<T>(array: readonly T[]): T | undefined
export function last(array: readonly []): undefined
export function last<T>(array: readonly T[]): T

export function last<T, U>(array: readonly T[], defaultValue: U): T | U
export function last<U>(array: readonly [], defaultValue: U): U
export function last<T, U>(array: readonly T[], defaultValue: U): T

export function last(array: readonly unknown[], defaultValue?: unknown) {
return array?.length > 0 ? array[array.length - 1] : defaultValue
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