7d22bb1c28
Also remove disclaimer about API instability since that is now implied by the 0.x version number of the Go module.
3.3 KiB
Persistent data structure in Go
This is a Go clone of Clojure's persistent data structures.
License is Eclipse Public License 1.0 (like Clojure).
Implementation notes
The list provided here is a singly-linked list and is very trivial to implement.
The implementation of persistent vector and hash map and based on a series of excellent blog posts as well as the Clojure source code. Despite the hash map appearing more complicated, the vector is slightly harder to implement due to the "tail array" optimization and some tricky transformation of the tree structure, which is fully replicated here.
Benchmarking results
Vectors
Compared to native slices,
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Adding elements is anywhere from 5x to 9x as slow.
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Read (sequential or random) is about 6x as slow.
Benchmarked on an MacBook Air (M1, 2020), with Go 1.17.5:
BenchmarkConjNativeN1-8 1779234 673.3 ns/op
BenchmarkConjNativeN2-8 948654 1220 ns/op
BenchmarkConjNativeN3-8 61242 20138 ns/op
BenchmarkConjNativeN4-8 1222 968176 ns/op
BenchmarkConjPersistentN1-8 264488 4462 ns/op 6.63x
BenchmarkConjPersistentN2-8 119526 9885 ns/op 8.10x
BenchmarkConjPersistentN3-8 6760 173995 ns/op 8.64x
BenchmarkConjPersistentN4-8 212 5576977 ns/op 5.76x
BenchmarkIndexSeqNativeN4-8 32031 37344 ns/op
BenchmarkIndexSeqPersistentN4-8 6145 192151 ns/op 5.15x
BenchmarkIndexRandNative-8 31366 38016 ns/op
BenchmarkIndexRandPersistent-8 5434 216284 ns/op 5.69x
BenchmarkEqualNative-8 110090 10738 ns/op
BenchmarkEqualPersistent-8 2121 557334 ns/op 51.90x
Hash map
Compared to native maps, adding elements is about 3-6x slow. Difference is more pronunced when keys are sequential integers, but that workload is very rare in the real world.
Benchmarked on an MacBook Air (M1, 2020), with Go 1.17.5:
goos: darwin
goarch: arm64
pkg: src.elv.sh/pkg/persistent/hashmap
BenchmarkSequentialConjNative1-8 620540 1900 ns/op
BenchmarkSequentialConjNative2-8 22918 52209 ns/op
BenchmarkSequentialConjNative3-8 567 2115886 ns/op
BenchmarkSequentialConjPersistent1-8 169776 7026 ns/op 3.70x
BenchmarkSequentialConjPersistent2-8 3374 354031 ns/op 6.78x
BenchmarkSequentialConjPersistent3-8 51 23091870 ns/op 10.91x
BenchmarkRandomStringsConjNative1-8 379147 3155 ns/op
BenchmarkRandomStringsConjNative2-8 10000 117332 ns/op
BenchmarkRandomStringsConjNative3-8 292 4034937 ns/op
BenchmarkRandomStringsConjPersistent1-8 96504 12207 ns/op 3.87x
BenchmarkRandomStringsConjPersistent2-8 1910 615644 ns/op 5.25x
BenchmarkRandomStringsConjPersistent3-8 33 31928604 ns/op 7.91x