mirror of
https://github.com/ethereum/solidity
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37 lines
1.1 KiB
ReStructuredText
37 lines
1.1 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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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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