What are the pitfalls when iterating over a map in Go?

When iterating over a map in Go, there are several important features and pitfalls:

1. The iteration order is not defined and can change — each time you iterate over a map, the order of keys may be different. You cannot rely on a fixed order.

2. Modifying the map during iteration — if you add or remove elements during iteration, the behavior is undefined and may lead to a panic or skipping elements.

3. Copying keys and values — during iteration, the variables for key and value are overwritten, so if you save their addresses, you may get unexpected results.

Example of incorrect key address saving:

m := map[string]int{"a":1, "b":2}
var keys []*string
for k := range m {
    keys = append(keys, &k) // all elements will point to the same variable k
}

Correct way is to create a copy inside the loop:

for k := range m {
    keyCopy := k
    keys = append(keys, &keyCopy)
}

In summary, when working with maps, it is important to remember the undefined order, not to modify the map during iteration, and to handle loop variables carefully.