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ICON2
What is ICON?
Getting Started
How to run a local network
How to run a Validator node
How to run an API Endpoint
How to create an ICON account
How to write a smart contract
How to use the JSON-RPC API
Concepts
Economics
Governance
Network
Computational utilities
ICON Stack
Intro to the stack
ICON execution environments
Smart contracts
Smart contract languages
Smart contract anatomy
Smart contract libraries
Building smart contracts
Testing smart contracts
Deploying smart contracts
Composability
Smart contract security
ICON networks
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Storage
IDEs
Projects
BTP & ICON Bridge
Decentralized applications (dApps)
ICON Improvement Proposals (IIPs)
Support
Support
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Advanced topics
Release notes
2022-04-11
2021-12-23
2021-12-20
2021-12-10
2021-12-07
2021-10-22
2021-10-12
2021-03-20
2021-03-04
2021-02-17
2020-09-03
2020-08-27
2020-08-23
2020-08-10
2020-04-08
2020-01-28
2019-12-19
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Smart contracts

What is a smart contract?

A smart contract is defined as follows by the ICON glossary:
Blockchain-integrated code for maintaining and interacting with data in a trusted, distributed database
They are represented by a specific type of ICON account, and can be distinguished by the prefix to the account address of cx. Smart contract accounts are deployed to the network and run in a deterministic manner based on their code. As such, they are not controlled by a user and a user cannot conduct manual actions that would override the smart contract logic.
​Wikipedia notes that they can be thought of as a regular legal contract with rules that are automatically executed, and thus the need for external enforcement or mediation is reduced.

Permissionless

Smart contracts can be written and deployed by anyone as long as they have an ICON account, the funds to deploy the contract, and the ability to produce a contract coded in a valid programming language for ICON.
Currently, smart contracts can be written in Java. Support may be available for other JVM languages as well, but this is highly untested.

Composability

Smart contracts are available to be called from other contracts by design. They act as open APIs so that one smart contract can make use of the already available and auditable sets of rules and actions reachable from the ICON ecosystem.
Learn more about composability in the corresponding section of the documentation.

Limitations

As mentioned in the sections on the ICON execution environments (e.g. Java), there are certain features of a runtime environment that are used and expected by many programmers that are not available in ICON. This is by design, so that the blockchain can be deterministic and a consensus can be formed about the global state. Some limitations are as follows:
  • No external networking
  • No randomness
Networking and external information can be made accessible through the use of oracles or external relays that aggregate proofs and communicate across blockchains.
Randomness on the blockchain is a work-in-progress. Some implementations are available, such as that from Chainlink.
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Smart contract languages
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Contents
What is a smart contract?
Permissionless
Composability
Limitations