Add comments about the performance of some methods

iter/gomap.go

@@ -25,6 +25,8 @@ func (*goMapIter[K, V]) Err() error {
 
 // FromMap produces an iterator of key-value pairs from a Go map.
 // The resulting iterator never returns an error.
+// Note that this is implemented in terms of [FromMapKeys],
+// which makes copies the keys of the map to a new slice.
 func FromMap[M ~map[K]V, K comparable, V any](m M) Of[Pair[K, V]] {
 	return &goMapIter[K, V]{
 		m:        m,
@@ -33,6 +35,8 @@ func FromMap[M ~map[K]V, K comparable, V any](m M) Of[Pair[K, V]] {
 }
 
 // FromMapKeys produces an iterator over the keys of a Go map.
+// Note that this is implemented in terms of [FromSlice],
+// after first copying the keys of the map to a new slice.
 func FromMapKeys[M ~map[K]V, K comparable, V any](m M) Of[K] {
 	keys := make([]K, 0, len(m))
 	for k := range m {

set/set.go

@@ -97,6 +97,7 @@ func (s Of[T]) Eachx(f func(T) error) error {
 // Iter produces an iterator over the members of the set,
 // in an indeterminate order.
 // The set may be nil.
+// Note that this makes a copy of the elements in the set.
 func (s Of[T]) Iter() iter.Of[T] {
 	return iter.FromMapKeys(s)
 }