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Add index parameter to filterMap callback signature#2

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lohmander merged 3 commits intomainfrom
copilot/update-filtermap-signature
Nov 4, 2025
Merged

Add index parameter to filterMap callback signature#2
lohmander merged 3 commits intomainfrom
copilot/update-filtermap-signature

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Copilot AI commented Nov 4, 2025 •
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The filterMap method callback only received the array element value, inconsistent with standard JavaScript array methods like map and filter which provide both value and index.

Changes

  • Maybe.filterMap: Updated signature to fn: (value: U, index: number) => Maybe<V>
  • AsyncMaybe.filterMap: Updated signature to fn: (value: U, index: number) => Maybe<V>
  • Functional wrapper: Updated all filterMap overloads to include index parameter

Usage

// Filter by position
Maybe.fromNullable(['a', 'b', 'c', 'd'])
  .filterMap((x, i) => i % 2 === 0 ? Maybe.fromNullable(x) : Maybe.fromNullable(null))
  .value(); // ['a', 'c']

// Use index in transformation
AsyncMaybe.fromPromise(Promise.resolve([10, 20, 30]))
  .filterMap((x, i) => Maybe.fromNullable(x + i))
  .value(); // Promise<[10, 21, 32]>

The change is backward compatible—existing code without index parameter continues to work.

Original prompt

This section details on the original issue you should resolve

<issue_title>filterMap does not provide an index</issue_title>
<issue_description>Currently filterMap has the signature filterMap(value: T): ..., but for an array mapping function it should include the index of the map item, i.e., filterMap(value: T, index: number).</issue_description>

<agent_instructions>Applies to Maybe, AsyncMaybe, and the fp version</agent_instructions>

Comments on the Issue (you are @copilot in this section)

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Copilot AI and others added 2 commits November 4, 2025 17:07
@lohmander
Initial exploration - plan to add index parameter to filterMap
828e252 
Co-authored-by: lohmander <2197050+lohmander@users.noreply.github.com>
@lohmander
Add index parameter to filterMap methods
7134d7f 
- Updated Maybe.filterMap to accept (value, index) callback
- Updated AsyncMaybe.filterMap to accept (value, index) callback
- Updated functional filterMap wrapper to pass index parameter
- Added comprehensive tests for all three implementations
- All tests passing (109 tests)

Co-authored-by: lohmander <2197050+lohmander@users.noreply.github.com>
Copilot AI changed the title [WIP] Update filterMap to include index parameter Add index parameter to filterMap callback signature Nov 4, 2025
Copilot AI requested a review from lohmander November 4, 2025 17:14
@lohmander lohmander marked this pull request as ready for review November 4, 2025 17:17
@lohmander lohmander merged commit fea82cd into main Nov 4, 2025
1 check passed
@lohmander lohmander deleted the copilot/update-filtermap-signature branch November 4, 2025 17:18
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filterMap does not provide an index

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