Generating first messages

We have set up our dependencies. Now let's use them to create simple messages.

Creating an instantiation message

For this step we will create a new file:

• src/contract.rs - here, we will define our messages and behavior of the contract upon receiving them

Add this module to src/lib.rs. You want it to be public, as users might want to get access to types stored inside your contract.

pub mod contract;

Now let's create an instantiate method for our contract. In src/contract.rs

use cosmwasm_std::{Response, StdResult};
use sylvia::contract;
use sylvia::types::InstantiateCtx;

pub struct CounterContract;

#[contract]
impl CounterContract {
    pub const fn new() -> Self {
        Self
    }

    #[sv::msg(instantiate)]
    pub fn instantiate(&self, _ctx: InstantiateCtx) -> StdResult<Response> {
        Ok(Response::default())
    }
}

So what is going on here? First, we define the CounterContract struct. It is empty right now but later when we learn about states, we will use its fields to store them. We mark the impl block with contract attribute macro. It will parse every method inside the impl block marked with the [sv::msg(...)] attribute and create proper messages and utilities like multitest helpers for them. More on them later.

CosmWasm contract requires only the instantiate entry point, and it is mandatory to specify it for the contract macro. We have to provide it with the proper context type InstantiateCtx.

Context gives us access to the blockchain state, information about our contract, and the sender of the message. We return the StdResult which uses standard CosmWasm error StdError. It's generic over Response. For now, we will return the default value of it.

I recommend expanding the macro now and seeing what Sylvia generates. It might be overwhelming, as there will be a lot of things generated that seem not relevant to our code, so for the bare minimum check the InstantiateMsg and its impl block.

Next step

If we build our contract with command:

contract $ cargo build --release --target wasm32-unknown-unknown --lib

and then run:

contract $ cosmwasm-check target/wasm32-unknown-unknown/release/contract.wasm

The output should look like this:

Available capabilities: {"stargate", "staking", "cosmwasm_1_3", "cosmwasm_2_0", "cosmwasm_1_1", "cosmwasm_1_2", "cosmwasm_1_4", "iterator"}

target/wasm32-unknown-unknown/release/contract.wasm: pass

All contracts (1) passed checks!