:sig
void DValue::each(std::function<void (const DValue& item, String key)> f) const

:params
f : callback invoked for each child, or once for a scalar value
return value : none

:see
>types
0_DValue
2_DValue_map
2_DValue_filter
2_DValue_is_list

:content
Iterates a `DValue` without modifying it. References are dereferenced before iteration.

For map-shaped values, the callback receives each child and its key. List-shaped maps iterate in numeric index order (`0`, `1`, `2`, ...); ordinary maps iterate in `std::map` string-key order. Scalar values invoke the callback once with the current value and an empty key.

:example
DValue user;
user["name"] = "Ada";
user["role"] = "admin";
StringList keys;
user.each([&](const DValue& item, String key) { keys.push_back(key); });
print(join(keys.sort(), ","), "\n");