ink! is an eDSL to write smart contracts in Rust for blockchains built on the Substrate framework. ink! contracts are compiled to WebAssembly.
Guided Tutorial for Beginners • ink! Documentation Portal • Developer Documentation
More relevant links:
- Substrate Stack Exchange ‒ Forum for getting your ink! questions answered
cargo-contract‒ CLI tool for ink! contracts
- Contracts UI ‒ Frontend for contract instantiation and interaction
- Substrate Contracts Node ‒ Simple Substrate blockchain which includes smart contract functionality
- We post announcements on Matrix and Discord (in the
Table of Contents
- Play with It
- Hello, World! ‒ The Flipper
- How it Works
- ink! Macros & Attributes Overview
- Developer Documentation
- Community Badges
Play with It
If you want to have a local setup you can use our
substrate-contracts-node for a quickstart.
It's a simple Substrate blockchain which includes the Substrate module for smart contract functionality ‒ the
contracts pallet (see How it Works for more).
We also have a live testnet on Rococo called Canvas. Canvas is a Substrate based parachain which supports ink! smart contracts. For further instructions on using this testnet, follow the instructions in the our documentation.
For both types of chains the Contracts UI can be used to instantiate your contract to a chain and interact with it.
A prerequisite for compiling smart contracts is to have Rust and Cargo installed. Here's an installation guide.
We recommend installing
cargo-contract as well.
It's a CLI tool which helps set up and manage WebAssembly smart contracts written with ink!:
cargo install cargo-contract --force
--force to ensure you are updated to the most recent
In order to initialize a new ink! project you can use:
cargo contract new flipper
This will create a folder
flipper in your work directory.
The folder contains a scaffold
Cargo.toml and a
lib.rs, which both contain the necessary building blocks for using ink!.
lib.rs contains our hello world contract ‒ the
Flipper, which we explain in the next section.
In order to build the contract just execute this command in the
cargo +nightly contract build
As a result you'll get a file
target/flipper.wasm file, a
metadata.json file and a
<contract-name>.contract file in the
target folder of your contract.
.contract file combines the Wasm and metadata into one file and needs to be used when instantiating the contract.
Hello, World! ‒ The Flipper
Flipper contract is a simple contract containing only a single
It provides methods to
- flip its value from
false(and vice versa) and
- return the current state.
Below you can see the code using the
ink_lang version of ink!.
use ink_lang as ink;
file in our examples folder contains exactly this code. Run
cargo contract build to build your
first ink! smart contract.
examples folder you'll find a number of examples written in ink!.
Some of the most interesting ones:
delegator‒ Implements cross-contract calling.
trait-erc20‒ Defines a trait for
Erc20contracts and implements it.
erc721‒ An exemplary implementation of
dns‒ A simple
- …and more, just rummage through the folder 🙃.
To build a single example navigate to the root of the example and run:
cargo contract build
You should now have an
<name>.contract file in the
target folder of the contract.
For information on how to upload this file to a chain, please have a look at the Play with It section or our smart contracts workshop.
How it Works
- Substrate's Framework for Runtime Aggregation of Modularized Entities (FRAME)
contains a module which implements an API for typical functions smart contracts need (storage,querying information about accounts, …).
This module is called the
contractspallet requires smart contracts to be uploaded to the blockchain as a Wasm blob.
- ink! is a smart contract language which targets the API exposed by
contracts. Hence ink! contracts are compiled to Wasm.
- When executing
cargo contract buildan additional file
metadata.jsonis created. It contains information about e.g. what methods the contract provides for others to call.
ink! Macros & Attributes Overview
In a module annotated with
#[ink::contract] these attributes are available:
||Defines the ink! storage struct. There can only be one ink! storage definition per contract.|
||Applicable to methods.||Flags a method for the ink! storage struct as message making it available to the API for calling the contract.|
||Applicable to method.||Flags a method for the ink! storage struct as constructor making it available to the API for instantiating the contract.|
||Defines an ink! event. A contract can define multiple such ink! events.|
||Applicable to ink! events.||Tells the ink! codegen to treat the ink! event as anonymous which omits the event signature as topic upon emitting. Very similar to anonymous events in Solidity.|
||Applicable on ink! event field.||Tells the ink! codegen to provide a topic hash for the given field. Every ink! event can only have a limited number of such topic field. Similar semantics as to indexed event arguments in Solidity.|
||Applicable to ink! messages.||Allows receiving value as part of the call of the ink! message. ink! constructors are implicitly payable.|
||Applicable to ink! messages and ink! constructors.||Specifies a concrete dispatch selector for the flagged entity. This allows a contract author to precisely control the selectors of their APIs making it possible to rename their API without breakage.|
||Applicable to ink! messages.||Specifies a fallback message that is invoked if no other ink! message matches a selector.|
||Applicable to ink! trait implementation blocks.||Changes the resulting selectors of all the ink! messages and ink! constructors within the trait implementation. Allows to disambiguate between trait implementations with overlapping message or constructor names. Use only with great care and consideration!|
||Applicable to ink! implementation blocks.||Tells the ink! codegen that some implementation block shall be granted access to ink! internals even without it containing any ink! messages or ink! constructors.|
See here for a more detailed description of those and also for details on the
#[ink::trait_definition] to define your very own trait definitions that are then implementable by ink! smart contracts.
See e.g. the
examples/trait-erc20 contract on how to utilize it or the documentation for details.
#[ink::test] procedural macro enables off-chain testing. See e.g. the
examples/erc20 contract on how to utilize those or the documentation for details.
We have a very comprehensive documentation portal, but if you are looking for the crate level documentation itself, then these are the relevant links:
||Language features exposed by ink!. See here for a detailed description of attributes which you can use in an
||Data structures available in ink!.|
||Low-level interface for interacting with the smart contract Wasm executor. Contains the off-chain testing API as well.|
||Common API for no_std and std to access alloc crate types.|
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Visit our contribution guidelines for more information.
Use the scripts provided under
scripts/check-* directory in order to run checks on either the workspace or all examples. Please do this before pushing work in a PR.
The entire code within this repository is licensed under the Apache License 2.0.
Please contact us if you have questions about the licensing of our products.