Merge pull request #3882 from ethereum/abi_doc

Document ABI encoding functions.

Changelog.md

@@ -8,6 +8,7 @@ Features:
  * General: Allow providing reason string for ``revert()`` and ``require()``.
  * General: Limit the number of errors output in a single run to 256.
  * General: Support accessing dynamic return data in post-byzantium EVMs.
+ * General: Add encoding routines ``abi.encodePacked``, ``abi.encode``, ``abi.encodeWithSelector`` and ``abi.encodeWithSignature``.
  * Interfaces: Allow overriding external functions in interfaces with public in an implementing contract.
  * Optimizer: Optimize ``SHL`` and ``SHR`` only involving constants (Constantinople only).
  * Optimizer: Remove useless ``SWAP1`` instruction preceding a commutative instruction (such as ``ADD``, ``MUL``, etc).

docs/miscellaneous.rst

@@ -317,6 +317,11 @@ The following is the order of precedence for operators, listed in order of evalu
 Global Variables
 ================
 
+- ``abi.encode(...) returns (bytes)``: :ref:`ABI <ABI>`-encodes the given arguments
+- ``abi.encodePacked(...) returns (bytes)``: Performes :ref:`packed encoding <abi_packed_mode>` of the given arguments
+- ``abi.encodeWithSelector(bytes4 selector, ...) returns (bytes)``: :ref:`ABI <ABI>`-encodes the given arguments
+   starting from the second and prepends the given four-byte selector
+- ``abi.encodeWithSignature(string signature, ...) returns (bytes)``: Equivalent to ``abi.encodeWithSelector(bytes4(keccak256(signature), ...)```
 - ``block.blockhash(uint blockNumber) returns (bytes32)``: hash of the given block - only works for 256 most recent, excluding current, blocks - deprecated in version 0.4.22 and replaced by ``blockhash(uint blockNumber)``.
 - ``block.coinbase`` (``address``): current block miner's address
 - ``block.difficulty`` (``uint``): current block difficulty

docs/units-and-global-variables.rst

@@ -44,9 +44,10 @@ Special Variables and Functions
 ===============================
 
 There are special variables and functions which always exist in the global
-namespace and are mainly used to provide information about the blockchain.
+namespace and are mainly used to provide information about the blockchain
+or are general-use utility functions.
 
-.. index:: block, coinbase, difficulty, number, block;number, timestamp, block;timestamp, msg, data, gas, sender, value, now, gas price, origin
+.. index:: abi, block, coinbase, difficulty, encode, number, block;number, timestamp, block;timestamp, msg, data, gas, sender, value, now, gas price, origin
 
 
 Block and Transaction Properties
@@ -90,6 +91,26 @@ Block and Transaction Properties
     You can only access the hashes of the most recent 256 blocks, all other
     values will be zero.
 
+.. index:: abi, encoding, packed
+
+ABI Encoding Functions
+----------------------
+
+- ``abi.encode(...) returns (bytes)``: ABI-encodes the given arguments
+- ``abi.encodePacked(...) returns (bytes)``: Performes packed encoding of the given arguments
+- ``abi.encodeWithSelector(bytes4 selector, ...) returns (bytes)``: ABI-encodes the given arguments
+   starting from the second and prepends the given four-byte selector
+- ``abi.encodeWithSignature(string signature, ...) returns (bytes)``: Equivalent to ``abi.encodeWithSelector(bytes4(keccak256(signature), ...)```
+
+.. note::
+    These encoding functions can be used to craft data for function calls without actually
+    calling a function. Furthermore, ``keccak256(abi.encodePacked(a, b))`` is a more
+    explicit way to compute ``keccak256(a, b)``, which will be deprecated in future
+    versions.
+
+See the documentation about the :ref:`ABI <ABI>` and the
+:ref:`tightly packed encoding <abi_packed_mode>` for details about the encoding.
+
 .. index:: assert, revert, require
 
 Error Handling