Golang map internal implementation - how does it search the map for a key?

Question

I\'ve read in "The Go Programming Language" that a "given key can be retrieved ... using a constant number of key comparisons on average, no matter how large

Answer 1

Maps are implemented as hash tables. There are plenty of places that explain hashing; Here's a nice visualization you can run.

One nice feature of Go is that

• the source is available on github, and
• it is pretty well written and documented, so it's not too hard to understand.

From the source file for hashmap:

// A map is just a hash table. The data is arranged
// into an array of buckets. Each bucket contains up to
// 8 key/value pairs. The low-order bits of the hash are
// used to select a bucket. Each bucket contains a few
// high-order bits of each hash to distinguish the entries
// within a single bucket.
//
// If more than 8 keys hash to a bucket, we chain on
// extra buckets.

https://github.com/golang/go/blob/master/src/runtime/map.go

One thing that you can learn from this code that is not normally covered in a lot of classes is how not to invalidate iterators when the map is resized internally.