Solidity: contract structure

Solidity： Contract structure

Contracts are similar to classes in oriented programming languages . Each contract can contain state variables 、 function 、 Function modifiers 、 event 、 Declaration of structure type and enumeration type .

There are also some special contracts, such as ： Libraries and interfaces

State variables

State variables are values that are permanently stored in the contract store

function

A function is an executable unit of code in a contract . Functions are usually defined inside contracts , But it can also be defined outside the contract

Function modifiers

Function modifiers can be used to improve function semantics declaratively

event

Events are convenient to call Ethereum virtual machine （EVM） Interface of log function

Structure

A structure is a custom type that can group several variables

Enumeration type

Enumeration types can be used to create a list of “ Constant values ” The custom types that make up the

Summary application code

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract Demo {
    uint data; // State variables 
    event deal(address seller, uint amount);// event 
    struct People {// Structure type 
        uint height;
        uint age;
        uint weight;
    }
    enum State{alive, die} // Enumeration type 
    modifier onlyMe(address seller){
        require(msg.sender == seller);
        _;
    }
    function transfer() public payable onlyMe(msg.sender) {// Function and added modifiers 
        emit deal(msg.sender, msg.value);
    }
}
    function hello(){// External function 

    }