mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
46 lines
1.6 KiB
ReStructuredText
46 lines
1.6 KiB
ReStructuredText
.. index:: ! contract;interface, ! interface contract
|
|
|
|
.. _interfaces:
|
|
|
|
**********
|
|
Interfaces
|
|
**********
|
|
|
|
Interfaces are similar to abstract contracts, but they cannot have any functions implemented. There are further restrictions:
|
|
|
|
- They cannot inherit other contracts or interfaces.
|
|
- All declared functions must be external.
|
|
- They cannot declare a constructor.
|
|
- They cannot declare state variables.
|
|
|
|
Some of these restrictions might be lifted in the future.
|
|
|
|
Interfaces are basically limited to what the Contract ABI can represent, and the conversion between the ABI and
|
|
an interface should be possible without any information loss.
|
|
|
|
Interfaces are denoted by their own keyword:
|
|
|
|
::
|
|
|
|
pragma solidity >=0.5.0 <0.8.0;
|
|
|
|
interface Token {
|
|
enum TokenType { Fungible, NonFungible }
|
|
struct Coin { string obverse; string reverse; }
|
|
function transfer(address recipient, uint amount) external;
|
|
}
|
|
|
|
Contracts can inherit interfaces as they would inherit other contracts.
|
|
|
|
All functions declared in interfaces are implicitly ``virtual``, which means that
|
|
they can be overridden. This does not automatically mean that an overriding function
|
|
can be overridden again - this is only possible if the overriding
|
|
function is marked ``virtual``.
|
|
|
|
Types defined inside interfaces and other contract-like structures
|
|
can be accessed from other contracts: ``Token.TokenType`` or ``Token.Coin``.
|
|
|
|
.. warning:
|
|
|
|
Interfaces have supported ``enum`` types since :doc:`Solidity version 0.5.0 <050-breaking-changes>`, make
|
|
sure the pragma version specifies this version as a minimum. |