mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
129 lines
2.7 KiB
ReStructuredText
129 lines
2.7 KiB
ReStructuredText
.. index:: contract, state variable, function, event, struct, enum, function;modifier
|
||
|
||
.. _contract_structure:
|
||
|
||
***********************
|
||
Structure of a Contract
|
||
***********************
|
||
|
||
Contracts in Solidity are similar to classes in object-oriented languages.
|
||
Each contract can contain declarations of :ref:`structure-state-variables`, :ref:`structure-functions`,
|
||
:ref:`structure-function-modifiers`, :ref:`structure-events`, :ref:`structure-structs-types` and :ref:`structure-enum-types`.
|
||
Furthermore, contracts can inherit from other contracts.
|
||
|
||
.. _structure-state-variables:
|
||
|
||
State Variables
|
||
===============
|
||
|
||
State variables are values which are permanently stored in contract storage.
|
||
|
||
::
|
||
|
||
contract SimpleStorage {
|
||
uint storedData; // State variable
|
||
// ...
|
||
}
|
||
|
||
See the :ref:`types` section for valid state variable types and
|
||
:ref:`visibility-and-accessors` for possible choices for
|
||
visibility.
|
||
|
||
.. _structure-functions:
|
||
|
||
Functions
|
||
=========
|
||
|
||
Functions are the executable units of code within a contract.
|
||
|
||
::
|
||
|
||
contract SimpleAuction {
|
||
function bid() { // Function
|
||
// ...
|
||
}
|
||
}
|
||
|
||
:ref:`function-calls` can happen internally or externally
|
||
and have different levels of visibility (:ref:`visibility-and-accessors`)
|
||
towards other contracts.
|
||
|
||
.. _structure-function-modifiers:
|
||
|
||
Function Modifiers
|
||
==================
|
||
|
||
Function modifiers can be used to amend the semantics of functions in a declarative way
|
||
(see :ref:`modifiers` in contracts section).
|
||
|
||
::
|
||
|
||
contract Purchase {
|
||
address public seller;
|
||
|
||
modifier onlySeller() { // Modifier
|
||
if (msg.sender != seller) throw;
|
||
_
|
||
}
|
||
|
||
function abort() onlySeller { // Modifier usage
|
||
// ...
|
||
}
|
||
}
|
||
|
||
in the section on contracts for a more in-depth explanation.
|
||
|
||
.. _structure-events:
|
||
|
||
Events
|
||
======
|
||
|
||
Events are convenience interfaces with the EVM logging facilities.
|
||
|
||
::
|
||
|
||
contract SimpleAuction {
|
||
event HighestBidIncreased(address bidder, uint amount); // Event
|
||
|
||
function bid() {
|
||
// ...
|
||
HighestBidIncreased(msg.sender, msg.value); // Triggering event
|
||
}
|
||
}
|
||
|
||
See :ref:`events` in contracts section for information on how events are declared
|
||
and can be used from within a dapp.
|
||
|
||
.. _structure-structs-types:
|
||
|
||
Structs Types
|
||
=============
|
||
|
||
Structs are custom defined types that can group several variables (see
|
||
:ref:`structs` in types section).
|
||
|
||
::
|
||
|
||
contract Ballot {
|
||
struct Voter { // Struct
|
||
uint weight;
|
||
bool voted;
|
||
address delegate;
|
||
uint vote;
|
||
}
|
||
}
|
||
|
||
.. _structure-enum-types:
|
||
|
||
Enum Types
|
||
==========
|
||
|
||
Enums can be used to create custom types with a finite set of values (see
|
||
:ref:`enums` in types section).
|
||
|
||
::
|
||
|
||
contract Purchase {
|
||
enum State { Created, Locked, Inactive } // Enum
|
||
}
|