Change value factory input argument in IAlternateLookup from TAlternateKey to TKey by Copilot · Pull Request #752 · bitfaster/BitFaster.Caching

Copilot · 2026-04-11T03:35:59Z

Summary

Changes the type of the value factory input argument in IAlternateLookup and IAsyncAlternateLookup from TAlternateKey to TKey.

Previously GetOrAdd / GetOrAddAsync passed the alternate key (e.g. ReadOnlySpan<char>) into the value factory. After this change the canonical cache key (TKey, e.g. string) is passed instead. This is more useful since the factory typically needs the strongly-typed key to produce the value, and it also avoids passing a potentially short-lived ref struct into a callback.

Changes

Interfaces

IAlternateLookup<TAlternateKey, TKey, TValue> – GetOrAdd / GetOrAdd<TArg> factory signatures changed from Func<TAlternateKey, …> to Func<TKey, …>
IAsyncAlternateLookup<TAlternateKey, TKey, TValue> – GetOrAddAsync / GetOrAddAsync<TArg> factory signatures changed from Func<TAlternateKey, …> to Func<TKey, …>

Implementations – all now pass actualKey (TKey) to the factory instead of key (TAlternateKey):

ConcurrentLruCore.cs (AlternateLookup & AsyncAlternateLookup structs)
ClassicLru.cs (AlternateLookup struct)
ConcurrentLfuCore.cs (AlternateLookup struct)
AtomicFactoryCache.cs (AlternateLookup struct)

Tests – updated factory lambdas to use TKey parameter:

ConcurrentLruAlternateLookupTests, ClassicLruAlternateLookupTests
ConcurrentLruAsyncAlternateLookupTests, ClassicLruAsyncAlternateLookupTests
ConcurrentLfuAlternateLookupTests, ConcurrentLfuAsyncAlternateLookupTests
AtomicFactoryCacheAlternateLookupTests
ConcurrentLruSoakTests

…te to TKey Agent-Logs-Url: https://github.com/bitfaster/BitFaster.Caching/sessions/29f900ac-3870-4bdc-9517-6807d80f09b5 Co-authored-by: bitfaster <12851828+bitfaster@users.noreply.github.com>

Copilot

Pull request overview

Updates the alternate-key lookup APIs so GetOrAdd/GetOrAddAsync value factories receive the canonical cache key type (TKey) rather than the alternate key type (TAlternateKey), and propagates that change through implementations and tests.

Changes:

Change IAlternateLookup/IAsyncAlternateLookup factory delegate signatures from Func<TAlternateKey,…> to Func<TKey,…>.
Update LRU/LFU/Atomic alternate-lookup implementations to pass actualKey (TKey) into the factory.
Update unit/soak tests to use the new TKey factory parameter type.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
BitFaster.Caching/Lru/ConcurrentLruCore.cs	Passes `actualKey` (K) into sync/async alternate-lookup factories.
BitFaster.Caching/Lru/ClassicLru.cs	Passes `actualKey` (K) into sync/async alternate-lookup factories.
BitFaster.Caching/Lfu/ConcurrentLfuCore.cs	Passes `actualKey` (K) into sync/async alternate-lookup factories.
BitFaster.Caching/IAsyncAlternateLookup.cs	Changes async factory delegate types to `Func<TKey,…>`.
BitFaster.Caching/IAlternateLookup.cs	Changes sync factory delegate types to `Func<TKey,…>`.
BitFaster.Caching/Atomic/AtomicFactoryCache.cs	Updates alternate-lookup adapter to accept `Func<K,…>` factories.
BitFaster.Caching.UnitTests/Lru/ConcurrentLruSoakTests.cs	Updates alternate-lookup soak factories to accept `string` key input.
BitFaster.Caching.UnitTests/Lru/ConcurrentLruAsyncAlternateLookupTests.cs	Updates async factory lambdas to use `TKey` parameter.
BitFaster.Caching.UnitTests/Lru/ConcurrentLruAlternateLookupTests.cs	Updates sync factory lambdas to use `TKey` parameter.
BitFaster.Caching.UnitTests/Lru/ClassicLruAsyncAlternateLookupTests.cs	Updates async factory lambdas to use `TKey` parameter.
BitFaster.Caching.UnitTests/Lru/ClassicLruAlternateLookupTests.cs	Updates sync factory lambdas to use `TKey` parameter.
BitFaster.Caching.UnitTests/Lfu/ConcurrentLfuAsyncAlternateLookupTests.cs	Updates async factory lambdas to use `TKey` parameter.
BitFaster.Caching.UnitTests/Lfu/ConcurrentLfuAlternateLookupTests.cs	Updates sync factory lambdas to use `TKey` parameter.
BitFaster.Caching.UnitTests/Atomic/AtomicFactoryCacheAlternateLookupTests.cs	Updates sync factory lambdas to use `TKey` parameter.

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            var result = await alternate.GetOrAddAsync("42".AsSpan(), key =>
            {
                factoryCalls++;
-                return Task.FromResult($"value-{key.ToString()}");
+                return Task.FromResult($"value-{key}");
            });


            var result = await alternate.GetOrAddAsync("42".AsSpan(), key =>
            {
                factoryCalls++;
-                return Task.FromResult($"value-{key.ToString()}");
+                return Task.FromResult($"value-{key}");
            });


            alternate.GetOrAdd(key, key =>
            {
                factoryCalls++;
-                return $"value-{key.ToString()}";
+                return $"value-{key}";
            }).Should().Be("value-42");


bitfaster · 2026-04-11T04:22:57Z

@copilot fix the build, update the xml doc issues in the code review and ensure all tests pass.

…rom AlternateKey to ActualKey Agent-Logs-Url: https://github.com/bitfaster/BitFaster.Caching/sessions/880908de-2e9a-47de-a736-2080c1044131 Co-authored-by: bitfaster <12851828+bitfaster@users.noreply.github.com>

Copilot · 2026-04-11T04:26:35Z

@copilot fix the build, update the xml doc issues in the code review and ensure all tests pass.

Done in d5c3b16:

Updated XML docs for valueFactory in both IAlternateLookup and IAsyncAlternateLookup to explicitly state the factory is invoked with the actual cache key (TKey)
Renamed all test methods that said ...UsesAlternateKey... to ...UsesActualKey... across the 7 affected test files
Build and all 107 alternate lookup tests pass

bitfaster · 2026-04-11T04:41:22Z

@copilot fix the benchmark so it can build and run.

…har>, int> to Func<string, int> Agent-Logs-Url: https://github.com/bitfaster/BitFaster.Caching/sessions/8e228955-be34-438b-b930-aba65302bb90 Co-authored-by: bitfaster <12851828+bitfaster@users.noreply.github.com>

Copilot · 2026-04-11T04:43:18Z

@copilot fix the benchmark so it can build and run.

Fixed in de68646. LruJustGetOrAddAlternate.cs and LfuJustGetOrAddAlternate.cs both had Func<ReadOnlySpan<char>, int> locals — updated to Func<string, int> to match the new factory signature. Benchmark project now builds cleanly on net9.0.

coveralls · 2026-04-11T05:04:54Z

coverage: 99.02%. first build — copilot/change-value-factory-input-type into main

Change value factory input argument in IAlternateLookup from TAlterna…

2f2f977

…te to TKey Agent-Logs-Url: https://github.com/bitfaster/BitFaster.Caching/sessions/29f900ac-3870-4bdc-9517-6807d80f09b5 Co-authored-by: bitfaster <12851828+bitfaster@users.noreply.github.com>

Copilot AI assigned Copilot and bitfaster Apr 11, 2026

Copilot created this pull request from a session on behalf of bitfaster April 11, 2026 03:36 View session

Copilot finished work on behalf of bitfaster April 11, 2026 03:36

Copilot AI requested a review from bitfaster April 11, 2026 03:36

bitfaster requested a review from Copilot April 11, 2026 04:10

Copilot started reviewing on behalf of bitfaster April 11, 2026 04:10 View session

Copilot AI reviewed Apr 11, 2026

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Copilot started work on behalf of bitfaster April 11, 2026 04:23 View session

Update XML docs to clarify valueFactory receives TKey; rename tests f…

d5c3b16

…rom AlternateKey to ActualKey Agent-Logs-Url: https://github.com/bitfaster/BitFaster.Caching/sessions/880908de-2e9a-47de-a736-2080c1044131 Co-authored-by: bitfaster <12851828+bitfaster@users.noreply.github.com>

Copilot finished work on behalf of bitfaster April 11, 2026 04:27

Copilot started work on behalf of bitfaster April 11, 2026 04:41 View session

Copilot finished work on behalf of bitfaster April 11, 2026 04:43

bitfaster approved these changes Apr 11, 2026

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bitfaster marked this pull request as ready for review April 11, 2026 22:07

bitfaster merged commit 089a440 into main Apr 11, 2026
16 checks passed

bitfaster deleted the copilot/change-value-factory-input-type branch April 11, 2026 22:08

Copilot AI mentioned this pull request Apr 11, 2026

Add GetAsyncAlternateLookup and TryGetAsyncAlternateLookup methods to IAsyncCache #751

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Change value factory input argument in IAlternateLookup from TAlternateKey to TKey#752

Change value factory input argument in IAlternateLookup from TAlternateKey to TKey#752
bitfaster merged 3 commits intomainfrom
copilot/change-value-factory-input-type

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bitfaster commented Apr 11, 2026

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