Merge the documentation about mappings

2 files changed, 27 insertions, 46 deletions

diff --git a/docs/frequently-asked-questions.rst b/docs/frequently-asked-questions.rst
index 6d47e4a7..353d8abc 100644
--- a/docs/frequently-asked-questions.rst
+++ b/docs/frequently-asked-questions.rst
@@ -104,52 +104,6 @@ This example demonstrates how to send funds from a contract to an address.
 
 See `endowment_retriever <https://github.com/fivedogit/solidity-baby-steps/blob/master/contracts/30_endowment_retriever.sol>`_.
 
-What is a ``mapping`` and how do we use them?
-=============================================
-
-A mapping is very similar to a K->V hashmap.
-If you have a state variable of type ``mapping (string -> uint) x;``, then you can
-access the value by ``x["somekeystring"]``.
-
-How can I get the length of a ``mapping``?
-==========================================
-
-Mappings are a rather low-level data structure. It does not store the keys
-and it is not possible to know which or how many values are "set". Actually,
-all values to all possible keys are set by default, they are just
-initialised with the zero value.
-
-In this sense, the attribute ``length`` for a mapping does not really apply.
-
-If you want to have a "sized mapping", you can use the iterable mapping
-(see below) or just a dynamically-sized array of structs.
-
-Are ``mapping``'s iterable?
-===========================
-
-Mappings themselves are not iterable, but you can use a higher-level
-datastructure on top of it, for example the `iterable mapping <https://github.com/ethereum/dapp-bin/blob/master/library/iterable_mapping.sol>`_.
-
-Can I put arrays inside of a ``mapping``? How do I make a ``mapping`` of a ``mapping``?
-=======================================================================================
-
-Mappings are already syntactically similar to arrays as they are, therefore it doesn't make much sense to store an array in them. Rather what you should do is create a mapping of a mapping.
-
-An example of this would be::
-
-    contract C {
-        struct myStruct {
-            uint someNumber;
-            string someString;
-        }
-
-        mapping(uint => mapping(string => myStruct)) myDynamicMapping;
-
-        function storeInMapping() {
-            myDynamicMapping[1]["Foo"] = myStruct(2, "Bar");
-        }
-    }
-
 Can you return an array or a ``string`` from a solidity function call?
 ======================================================================
 
diff --git a/docs/types.rst b/docs/types.rst
index 5fb512d5..959d4de3 100644
--- a/docs/types.rst
+++ b/docs/types.rst
@@ -617,6 +617,33 @@ Because of this, mappings do not have a length or a concept of a key or value be
 Mappings are only allowed for state variables (or as storage reference types
 in internal functions).
 
+It is possible to mark mappings ``public`` and have Solidity create an accessor.
+The ``_KeyType`` will become a required parameter for the accessor and it will
+return ``_ValueType``.
+
+::
+
+    pragma solidity ^0.4.0;
+
+    contract MappingExample {
+        mapping(address => uint) public balances;
+
+        function update(uint newBalance) {
+            balances[msg.sender] = newBalance;
+        }
+    }
+
+    contract MappingUser {
+        function f() returns (uint) {
+            return MappingExample(<address>).balances(this);
+        }
+    }
+
+
+.. note::
+  Mappings are not iterable, but it is possible to implement a data structure on top of them.
+  For an example, see `iterable mapping <https://github.com/ethereum/dapp-bin/blob/master/library/iterable_mapping.sol>`_.
+
 .. index:: assignment, ! delete, lvalue
 
 Operators Involving LValues