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https://github.com/ethereum/solidity
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46 lines
1.6 KiB
ReStructuredText
46 lines
1.6 KiB
ReStructuredText
.. index:: ! contract;interface, ! interface contract
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.. _interfaces:
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**********
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Interfaces
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**********
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Interfaces are similar to abstract contracts, but they cannot have any functions implemented. There are further restrictions:
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- They cannot inherit other contracts or interfaces.
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- All declared functions must be external.
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- They cannot declare a constructor.
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- They cannot declare state variables.
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Some of these restrictions might be lifted in the future.
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Interfaces are basically limited to what the Contract ABI can represent, and the conversion between the ABI and
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an interface should be possible without any information loss.
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Interfaces are denoted by their own keyword:
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::
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pragma solidity >=0.5.0 <0.7.0;
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interface Token {
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enum TokenType { Fungible, NonFungible }
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struct Coin { string obverse; string reverse; }
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function transfer(address recipient, uint amount) external;
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}
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Contracts can inherit interfaces as they would inherit other contracts.
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All functions declared in interfaces are implicitly ``virtual``, which means that
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they can be overridden. This does not automatically mean that an overriding function
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can be overridden again - this is only possible if the overriding
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function is marked ``virtual``.
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Types defined inside interfaces and other contract-like structures
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can be accessed from other contracts: ``Token.TokenType`` or ``Token.Coin``.
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.. warning:
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Interfaces have supported ``enum`` types since :doc:`Solidity version 0.5.0 <050-breaking-changes>`, make
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sure the pragma version specifies this version as a minimum. |