# A Fast Immutable Map in Go

DevFeed: [A Fast Immutable Map in Go](<https://devfeed.tech/articles/a-fast-immutable-map-in-go-29398.md>)

Original publisher: [Read original article](<https://lemire.me/blog/2026/03/29/a-fast-immutable-map-in-go/>)

Author: Daniel Lemire

Published: 2026-03-29T18:18:01Z

Content type: article

Language: en

Sources: [Daniel Lemire](<https://devfeed.tech/sources/daniel-lemire.md>)

Topics: [Go Language](<https://devfeed.tech/topics/go-language.md>), [Data structures](<https://devfeed.tech/topics/data-structures.md>)

Tags: [benchmarks](<https://devfeed.tech/tags/benchmarks.md>), [go](<https://devfeed.tech/tags/go.md>), [map](<https://devfeed.tech/tags/map.md>), [memory](<https://devfeed.tech/tags/memory.md>)

## AI overview

The article presents constmap, a Go library for immutable string-to-value maps built with binary fuse filters. For fixed key sets, it aims to reduce memory use and provide fast lookups; benchmarks on one million keys reported nearly three times faster lookups and sixfold lower memory use than Go's standard map on the author's test system.

## Source excerpt

Consider the following problem. You have a large set of strings, maybe millions. You need to map these strings to 8-byte integers (uint64). These integers are given to you. If you are working in Go, the standard solution is to create a map. The construction is trivial, something like the following loop. m := make(map[string]uint64, ... Continue reading A Fast Immutable Map in Go