Home Blockchain Education Contracts in Solidity

Contracts in Solidity

Contracts in Solidity are similar to classes in object-oriented languages. Each contract can contain declarations of State VariablesFunctionsFunction ModifiersEventsStruct Types and Enum Types. Furthermore, contracts can inherit from other contracts.

There are also special kinds of contracts called libraries and interfaces.

The section about contracts contains more details than this section, which serves to provide a quick overview.

State Variables

State variables are variables whose values are permanently stored in contract storage.

pragma solidity >=0.4.0 <0.7.0;

contract SimpleStorage {
    uint storedData; // State variable
    // ...

See the Types section for valid state variable types and Visibility and Getters for possible choices for visibility.


Functions are the executable units of code within a contract.

pragma solidity >=0.4.0 <0.7.0;

contract SimpleAuction {
    function bid() public payable { // Function
        // ...

Function Calls can happen internally or externally and have different levels of visibility towards other contracts. Functions accept parameters and return variables to pass parameters and values between them.

Function Modifiers

Function modifiers can be used to amend the semantics of functions in a declarative way (see Function Modifiers in the contracts section).

pragma solidity >=0.4.22 <0.7.0;

contract Purchase {
    address public seller;

    modifier onlySeller() { // Modifier
            msg.sender == seller,
            "Only seller can call this."

    function abort() public view onlySeller { // Modifier usage
        // ...


Events are convenience interfaces with the EVM logging facilities.

pragma solidity >=0.4.21 <0.7.0;

contract SimpleAuction {
    event HighestBidIncreased(address bidder, uint amount); // Event

    function bid() public payable {
        // ...
        emit HighestBidIncreased(msg.sender, msg.value); // Triggering event

See Events in contracts section for information on how events are declared and can be used from within a dapp.

Struct Types

Structs are custom defined types that can group several variables (see Structs in types section).

pragma solidity >=0.4.0 <0.7.0;

contract Ballot {
    struct Voter { // Struct
        uint weight;
        bool voted;
        address delegate;
        uint vote;

Enum Types

Enums can be used to create custom types with a finite set of ‘constant values’ (see Enums in types section).

pragma solidity >=0.4.0 <0.7.0;

contract Purchase {
    enum State { Created, Locked, Inactive } // Enum

Source link

Must Read


As the world tries to grapple with the implications of 5G, researchers from China have already started looking into 6G. 6G will operate on...

Building a Continuous Integration pipeline

What is continuous integration? In the event that you haven’t used continuous integration systems in the past, let’s do a quick run through of what...

IOHK Joins Hyperledger

Leading blockchain research and development company behind Cardano, IOHK, has joined the Hyperledger consortium. Hyperledger is an open-source community focused on developing a suite of...

Transforming the pension system using blockchain

 When teachers retire, they expect accurate pension payouts. That’s also the goal of plan administrators, who have an obligation to ensure pension system integrity.Still,...

Business utilities of Machine Learning & Predictive Analytics

What’s the first thing that comes to mind when you hear “artificial intelligence” (AI)? While I-Robot was a great film, it doesn’t count. Many don’t realize how...

Google Meet gets AI based noise cancellation for video calls

Google has added a new noise cancellation feature on Google Meet that uses Artificial Intelligence (AI) to cancel out the noise in the background...

Highlighting AI Bias

On Monday, IBM made a monumental announcement: the company is getting out of the facial recognition business, citing racial justice concerns and the need...

Understanding Federal IT

http://www.podcastone.com/downloadsecurity?url=aHR0cHM6Ly9wZHN0LmZtL2UvY2h0YmwuY29tL3RyYWNrL0UyRzg5NS9hdy5ub3hzb2x1dGlvbnMuY29tL2xhdW5jaHBvZC9hZHN3aXp6LzE3MDYvMDYwOWZlZGVyYWx0ZWNodGFsa19wb2RjYXN0X21scDJfYWQyNzk4OWMubXAzP2F3Q29sbGVjdGlvbklkPTE3MDYmYXdFcGlzb2RlSWQ9N2UwNDEzYWItZmEyZi00YTdjLWJlMWItZmQwZmFkMjc5ODljKip8MTU5MjM4Nzc5NTM2OCoqfA==.mp3This week on Federal Tech Talk, host John Gilroy interviews Chase Cunningham, principal analyst serving security and risk professionals at Forrester Research. Cunningham has four patents,...

Artificial Brains Need Sleep Too

 States that resemble sleep-like cycles in simulated neural networks quell the instability that comes with uninterrupted self-learning in artificial analogs of brains.No one can...

Differenciating Bitcoin and Electronic Money

Bitcoin has the largest market share among virtual currencies, and is already being used on a daily basis overseas. Since it is a virtual...
banner image