Creating an ink! Project

ink! is an Embedded Domain Specific Language (eDSL): a domain-specific language of the Rust programming language. That means:

• we allow only a subset of the Rust programming language features to be used for writing smart contracts. For example, it is not possible do any multi-threading operations or access the web.
• we provide annotations, macros, and primitives that are needed when writing smart contracts. For example, annotations on what the smart contract's storage struct is or what an event is.

ink! is just standard Rust in a well-defined "contract format" with specialized #[ink(…)] attribute macros. These attribute macros tell ink! what the different parts of your Rust smart contract represent, and ultimately allow ink! to do all the magic needed to create Polkadot SDK compatible RISC-V bytecode!

Create a new project

Use the ink! CLI to generate an initial smart contract with some scaffolding code.

Make sure you are in your working directory, and then run:

$ cargo contract new flipper

This command will create a new project folder named flipper with this content:

flipper
  └─ lib.rs         <-- Contract Source Code
  └─ Cargo.toml     <-- Rust Dependencies and ink! Configuration
  └─ .gitignore

Contract Source Code

For the lib.rs file, cargo-contract automatically generates the source code for the "Flipper" contract, which is about the simplest "smart" contract you can build. You can take a sneak peak as to what will come by looking at the source code here: Flipper Example Source Code.

The Flipper contract is nothing more than a bool which gets flipped from true to false through the flip() function.

Testing Your Contract

At the bottom of the lib.rs you'll see some simple test cases which verify the functionality of the contract. We can quickly test this code is functioning as expected:

$ cargo test

To which you should see a successful test completion:

$ cargo test
running 2 tests
test flipper::tests::it_works ... ok
test flipper::tests::default_works ... ok

test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

Now that we are feeling confident things are working, we can actually compile this contract to a RISC-V binary in the next step.