write-package.md

title
Write a Sui Move Package

In order to build a Move package and run code defined in this package, first install Sui binaries and clone the repository as this tutorial assumes you have the Sui repository source code in your current directory.

Refer to the code example developed for this tutorial in the m1.move file.

The directory structure used in this tutorial should at the moment look as follows (assuming Sui has been cloned to a directory called "sui"):

current_directory
├── sui

For convenience, make sure the path to Sui binaries (~/.cargo/bin), including the sui command used throughout this tutorial, is part of your system path:

$ which sui

Creating the directory structure

Now proceed to creating a package directory structure in the current directory, parallel to the sui repository. It will contain an empty manifest file and an empty module source file following the Move code organization described earlier.

So from the same directory containing the sui repository create a parallel directory to it by running:

$ mkdir -p my_move_package/sources
touch my_move_package/sources/m1.move
touch my_move_package/Move.toml

The directory structure should now be (please note that directories at the same indentation level in the figure below should also be at the same level in the file system):

current_directory
├── sui
├── my_move_package
    ├── Move.toml
    ├── sources
        ├── m1.move

Defining the package

Let us assume that our module is part of an implementation of a fantasy game set in medieval times, where heroes roam the land slaying beasts with their trusted swords to gain prizes. All of these entities will be represented by Sui objects; in particular, we want a sword to be an upgradable asset that can be shared between different players. A sword asset can be defined similarly to another asset we are already familiar with from our First look at Move source code. That is a Coin struct type.

Let us put the following module and struct definitions in the m1.move file:

module my_first_package::m1 {
    use sui::object::Info;
    use sui::tx_context::TxContext;

    struct Sword has key, store {
        info: Info,
        magic: u64,
        strength: u64,
    }
}

Since we are developing a fantasy game, in addition to the mandatory id field as well as key and store abilities (same as in the Coin struct), our asset has both magic and strength fields describing its respective attribute values. Please note that we need to import the Object package from Sui framework to gain access to the Info struct type defined in this package.

If we want to access sword attributes from a different package, we need to add accessor functions to our module similar to the value function in the Coin package described in Move functions (please make sure you add these functions, and all the following code in this tutorial, in the scope of our package - between curly braces starting and ending the package definition):

    public fun magic(self: &Sword): u64 {
        self.magic
    }

    public fun strength(self: &Sword): u64 {
        self.strength
    }

In order to build a package containing this simple module, we need to put some required metadata into the Move.toml file, including package name, package version, local dependency path to locate Sui framework code, and package numeric ID, which must be 0x0 for user-defined modules to facilitate package publishing.

[package]
name = "MyFirstPackage"
version = "0.0.1"

[dependencies]
Sui = { local = "../sui/crates/sui-framework" }

[addresses]
my_first_package = "0x0"

See the Move.toml file used in our end-to-end tutorial for an example.