Why Is the Iteration Order of Go Map Keys Not Guaranteed and Often Appears Random?

Go: Understanding Iteration Order in Map Keys

In the Go programming language, maps are implemented as hashmaps. The iteration order of map keys is not explicitly specified in the Go Programming Language Specification, as it can vary depending on the implementation.

Hash Function and Equivalence

The Go runtime utilizes a unified hashmap implementation written in C. The only variations between map[string]T and map[byte]T lie in the hash function, equivalence function, and copy function.

Ordered vs. Randomized Iteration

Prior to Go 1, the iteration order of map keys was insertion-order dependent only when key collisions occurred. Otherwise, the order was independent of key type or insertion sequence.

However, in the latest Go weekly release and Go 1, the iteration order has been randomized. A pseudo-randomly chosen key initiates the iteration, with hashcode computation seeded by a pseudo-random number. This change ensures that the ordering is different each time a program is run, even with the same input data.

String Maps: A Coincidence

Your observation that string maps apparently have a predictable iteration order was coincidental. While the order may remain constant for a particular run, it is not guaranteed and can vary across different executions.

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