Write a Module

Create and deploy your first move module.

If you have not already, open your newly initiatlized project within your code editor of choice on your host machine. Remember, the container configs directory is bound to the supra_configs directory on your host machine. Any changes made to these files on the host machine will be reflected within the container.

If you are using VS Code, we highly recommend that you install the Supra Move extension.

1

Create a new move file within the sources directory.

In the previous step, we set the named address of @exampleAddress to that of your own account. Notice how the name of this module is exampleAddress::transfer. Modules are defined with the following format: ADDRESS::MODULE_NAME In Move, global storage is a forest with trees rooted at an account address. Accounts can store both resource data and module code. Modules are deployed to an account, rather than a unique address being generated at deployment as you may be custom to with other VMs. At compilation, exampleAddress will be replaced with the value you set in the named addresses within the Move.toml file. Upon publishing the module, it will be published at that designated account.

The sources directory holds the move modules that you will be working on within your project. Within the sources directory, create the example.move file with the following code.

example.move

module exampleAddress::transfer {

    use supra_framework::supra_coin;
    use supra_framework::coin;

    // Function to transfer the specified amount to two destinations from the source signer
    public entry fun two_by_two(
        first: &signer,
        amount_first: u64,
        dst_first: address,
        dst_second: address,
    ) {
        // Transfer the specified amount to the first destination
        coin::transfer<supra_coin::SupraCoin>(first, dst_first,amount_first);
        // Transfer the same amount to the second destination
        coin::transfer<supra_coin::SupraCoin>(first,dst_second, amount_first);
    }

     // Function to view the balance of an address
    #[view]
    public fun view_balance(address: address): u64 {
        coin::balance<supra_coin::SupraCoin>(address)
    }

}

The two_by_two function provided has four parameters. The signer, amount to be transferred, and two destination addresses. The function will transfer the passed amount to both destination addresses.

Signer is a built-in Move resource. It indicates which account is responsible for calling the transaction. This value is automatically injected by the VM and not passed by the user.