Returns the value for a given key, or an optional default value if the key
could not be found.
Note:
Keys of type object are supported.
If an object implements Ds\Hashable,
equality will be determined by the object's equals function.
If an object does not implement Ds\Hashable,
objects must be references to the same instance to be considered equal.
Note:
You can also use array syntax to access values by key, eg. $map["key"].
Caution
Be careful when using array syntax. Scalar keys will be coerced to
integers by the engine. For example, $map["1"] will attempt
to access int(1), while $map->get("1") will
correctly look up the string key.