lib: add `provide_default_value` in Map to allow subclasses to provide

[nit.git] / lib / standard / collection / abstract_collection.nit

diff --git a/lib/standard/collection/abstract_collection.nit b/lib/standard/collection/abstract_collection.nit
index d975715..18bac96 100644 (file)
--- a/lib/standard/collection/abstract_collection.nit
+++ b/lib/standard/collection/abstract_collection.nit
@@ -223,7 +223,7 @@ end
 
 # Abstract sets.
 #
-# Set contains contains only one element with the same value (according to ==).
+# Set is a collection without ducplicates (according to ==)
 #      var s: Set[String] = new ArraySet[String]
 #      var a = "Hello"
 #      var b = "Hel" + "lo"
@@ -280,6 +280,20 @@ interface MapRead[K: Object, E]
        # Get the item at `key`.
        fun [](key: K): E is abstract
 
+       # Get the item at `key` or null if `key` is not in the map.
+       #
+       #     var x = new HashMap[String, Int]
+       #     x["four"] = 4
+       #     assert x.get_or_null("four") == 4
+       #     assert x.get_or_null("five") == null
+       #
+       # Note: use `has_key` and `[]` if you need the distinction bewteen a key associated with null, and no key.
+       fun get_or_null(key: K): nullable E
+       do
+               if has_key(key) then return self[key]
+               return null
+       end
+
        # Get the item at `key` or return `default` if not in map
        fun get_or_default(key: K, default: E): E
        do
@@ -308,6 +322,13 @@ interface MapRead[K: Object, E]
 
        # Number of items in the collection.
        fun length: Int is abstract
+
+       # Called by the underling implementation of `[]` to provide a default value when a `key` has no value
+       # By default the behavior is to abort.
+       #
+       # Note: the value is returned *as is*, implementations may want to store the value in the map before returning it
+       # @toimplement
+       protected fun provide_default_value(key: K): E do abort
 end
 
 # Maps are associative collections: `key` -> `item`.
@@ -531,7 +552,7 @@ interface CoupleMap[K: Object, E]
        do
                var c = couple_at(key)
                if c == null then
-                       abort
+                       return provide_default_value(key)
                else
                        return c.second
                end