Null-aware operator with Maps

Question

I had the same problem with lists, now it is Map.

What I would like to do

The following syntax is not Dart, as in it does not

Answer 1

I use this function for null-safe nested map access:

// Returns value of map[p1][p2]...[pn]
// where path = [p1, p2, ..., pn]
//
// example: mapGet(map, ["foo", 9, 'c'])
dynamic mapGet(Map map, List path) {
  assert(path.length > 0);
  var m = map ?? const {};
  for (int i = 0; i < path.length - 1; i++) {
      m = m[path[i]] ?? const {};
  }

  return m[path.last];
}

Answer 2

Yet another syntax I used a few times:

map?.containsKey(key) ?? false ? map[key] : otherValue

Although functionally equivalent to the one proposed by @Günter Zöchbauer it is a bit more cumbersome.
Anyway, since it might look clearer in a few circumstances, it is worth to mention.

Answer 3

This works:

(map ?? const {})[key] ?? otherValue;

Because the key will fallback to accessing an empty Map, which will always return null.

Answer 4

Or

map != null ? map[key]: otherValue;

which checks to see if the map is null before attempting to access the variable, which is the same as Günter's answer but checks first.

Answer 5

Something like this might work as an extension function:

extension MapExtensions<T, K> on Map<T, K> {
  K getOrNull(T key) {
     if (this == null || !this.containsKey(key)) {
       return null;
     } else {
       return this[key];
     }
  }

  K getOrElse(T key, K fallback) {
    return this.getOrNull(key) ?? fallback;
  }
}

Note: I haven't tested this, but should work.