Wrapped maps with default values

Gosu provides a class called gw.util.AutoMap that implements the Java interface java.util.Map and the Gosu interface gw.lang.reflect.gs.IGosuObject. This class provides an alternative to using the standard java.util.HashMap class.

The AutoMap<K,V> class provides a default value for the map if the key is not present. When you create an AutoMap object, you pass a Gosu block into the constructor. If your code calls get on the map and its value is null, Gosu runs the mapping block that you provide. Gosu takes the return value from the block, stores it in the map for that key, and returns the value to the original caller. All other methods delegate directly to the wrapped map.

The simplest constructor takes only one argument, which is a Gosu block that provides a default value. The block takes one argument, which is the key, and returns the default value to use. If you use this constructor, Gosu creates a new instance of java.util.HashMap as its wrapped map.

Another constructor takes a map (any object whose class implements java.util.Map) as the first argument and the Gosu block as the second argument. Use this alternative constructor if you have an existing map that you want to wrap rather than create a new map.

For example, the following code assigns values in a new map to entries that do not have values in the original map:

var origMap = { 1 -> "apple", 4 -> "orange"}
var newMap = origMap.toAutoMap( \ k -> "I want ${k} blueberries")
for (i in 1..5) {
  print(newMap[i])
}

This code prints:

apple
I want 2 blueberries
I want 3 blueberries
orange
I want 5 blueberries

var mapper = new HashMap<String, String>()
mapper.put("aKey", "aValue")
mapper.put("bKey", "bValue")
var automap = mapper.toAutoMap(\k -> k)

automap.clear()
print(automap.entrySet())

[]

automap.entrySet() //Returns [bKey=bValue, aKey=aValue]

automap.hashCode() //Returns 1447807072

automap.keySet() //Returns [bKey, aKey]

automap.put("newKey", "newValue")
print(automap.entrySet())

[bKey=bValue, aKey=aValue, newKey=newValue]

var mapper2 = new HashMap<String, String>()
                                    mapper2.put("aKey2", "aValue2")
                                    mapper2.put("bKey2", "bValue2")
                                    automap.putAll(mapper2)
                                    print(automap.entrySet())

[bKey=bValue, aKey=aValue, bKey2=bValue2, aKey2=aValue2]

automap.remove("aKey")
print(automap.entrySet())

[bKey=bValue]

automap.values() //Returns [bValue, aValue]