Strings

len does not return the number of characters: Strings

Maps

Maps don't free that much memory as they shrink.
Shoutouts to: https://100go.co/28-maps-memory-leaks/

func main() {
    n := 1_000_000
    m := make(map[int][128]byte)
    printAlloc()

    for i := 0; i < n; i++ { // Adds 1 million elements
        m[i] = [128]byte{}
    }
    printAlloc()

    for i := 0; i < n; i++ { // Deletes 1 million elements
        delete(m, i)
    }

    runtime.GC() // Triggers a manual GC
    printAlloc()
    runtime.KeepAlive(m) // Keeps a reference to m so that the map isn’t collected
}

func printAlloc() {
    var m runtime.MemStats
    runtime.ReadMemStats(&m)
    fmt.Printf("%d MB\n", m.Alloc/(1024*1024))
}

Will print:

0 MB
382 MB
287 MB

TL:DR; Go Maps grow but never shrink. To avoid this, re-assign the map.

Strings

Maps

Functions