Is it safe to remove selected keys from map within a range loop?

How can one remove selected keys from a map? Is it safe to combine delete() with range, as in the code below?

package main

import "fmt"

type Info struct {
    value string
}

func main() {
    table := make(map[string]*Info)

    for i := 0; i < 10; i++ {
        str := fmt.Sprintf("%v", i)
        table[str] = &Info{str}
    }

    for key, value := range table {
        fmt.Printf("deleting %v=>%v\n", key, value.value)
        delete(table, key)
    }
}

https://play.golang.org/p/u1vufvEjSw

This is safe! You can also find a similar sample in Effective Go:

for key := range m {
    if key.expired() {
        delete(m, key)
    }
}

And the language specification:

The iteration order over maps is not specified and is not guaranteed to be the same from one iteration to the next. If map entries that have not yet been reached are removed during iteration, the corresponding iteration values will not be produced. If map entries are created during iteration, that entry may be produced during the iteration or may be skipped. The choice may vary for each entry created and from one iteration to the next. If the map is nil, the number of iterations is 0.

Sebastian's answer is accurate, but I wanted to know why it was safe, so I did some digging into the Map source code. It looks like on a call to delete(k, v), it basically just sets a flag (as well as changing the count value) instead of actually deleting the value:

b->tophash[i] = Empty;

(Empty is a constant for the value 0)

What the map appears to actually be doing is allocating a set number of buckets depending on the size of the map, which grows as you perform inserts at the rate of 2^B (from this source code):

byte    *buckets;     // array of 2^B Buckets. may be nil if count==0.

So there are almost always more buckets allocated than you're using, and when you do a range over the map, it checks that tophash value of each bucket in that 2^B to see if it can skip over it.

To summarize, the delete within a range is safe because the data is technically still there, but when it checks the tophash it sees that it can just skip over it and not include it in whatever range operation you're performing. The source code even includes a TODO:

 // TODO: consolidate buckets if they are mostly empty
 // can only consolidate if there are no live iterators at this size.

This explains why using the delete(k,v) function doesn't actually free up memory, just removes it from the list of buckets you're allowed to access. If you want to free up the actual memory you'll need to make the entire map unreachable so that garbage collection will step in. You can do this using a line like

map = nil