Creating Custom Objects

Objects are the fundamental units of storage on Sui. This guide covers how to create custom objects with different properties and behaviors.

Object Basics

All objects on Sui must have a unique identifier (UID) and the key ability.

Minimal Object

module my_package::basic {
    use sui::object::{Self, UID};

    public struct BasicObject has key {
        id: UID,
    }

    public fun create(ctx: &mut TxContext): BasicObject {
        BasicObject {
            id: object::new(ctx),
        }
    }
}

Object Abilities

Abilities define what operations can be performed on a struct.

The Four Abilities

key: Can be used as a top-level object (required for all Sui objects)
store: Can be stored inside other objects
copy: Can be copied
drop: Can be discarded/destroyed implicitly

Common Ability Combinations

// Standard owned object
public struct OwnedNFT has key, store {
    id: UID,
    name: String,
}

// Cannot be stored (soulbound)
public struct SoulboundBadge has key {
    id: UID,
    owner: address,
}

// Can be copied (witness pattern)
public struct Witness has drop {}

// Inner object (can be stored)
public struct Metadata has store {
    name: String,
    value: u64,
}

Object Types

Owned Objects

Objects owned by an address. This is the most common type. From examples/move/nft:

module examples::testnet_nft {
    use std::string;
    use sui::url::{Self, Url};

    public struct TestnetNFT has key, store {
        id: UID,
        name: string::String,
        description: string::String,
        url: Url,
    }

    public fun mint_to_sender(
        name: vector<u8>,
        description: vector<u8>,
        url: vector<u8>,
        ctx: &mut TxContext,
    ) {
        let sender = ctx.sender();
        let nft = TestnetNFT {
            id: object::new(ctx),
            name: string::utf8(name),
            description: string::utf8(description),
            url: url::new_unsafe_from_bytes(url),
        };
        transfer::public_transfer(nft, sender);
    }
}

Nested Objects

Objects can contain other objects with the store ability:

module my_package::nested {
    public struct Metadata has store {
        title: String,
        creator: address,
    }

    public struct NFT has key, store {
        id: UID,
        metadata: Metadata,  // Nested object
        attributes: vector<Attribute>,
    }

    public struct Attribute has store {
        key: String,
        value: String,
    }
}

Objects with Options

module my_package::inventory {
    use sui::object::UID;

    public struct Hero has key, store {
        id: UID,
        health: u64,
        sword: Option<Sword>,  // May or may not have a sword
    }

    public struct Sword has key, store {
        id: UID,
        strength: u64,
    }

    public fun equip(hero: &mut Hero, sword: Sword) {
        assert!(hero.sword.is_none(), EAlreadyEquipped);
        hero.sword.fill(sword);
    }

    public fun unequip(hero: &mut Hero): Sword {
        assert!(hero.sword.is_some(), ENotEquipped);
        option::extract(&mut hero.sword)
    }
}

Real-World Example: Game Characters

From examples/move/hero:

module hero::example {
    use sui::balance::{Self, Balance};
    use sui::coin::{Self, Coin};
    use sui::sui::SUI;

    /// Game character with attributes and inventory
    public struct Hero has key, store {
        id: UID,
        game_id: ID,
        health: u64,
        experience: u64,
        sword: Option<Sword>,
    }

    /// Weapon with magic and strength
    public struct Sword has key, store {
        id: UID,
        game_id: ID,
        magic: u64,
        strength: u64,
    }

    /// Consumable healing item
    public struct Potion has key, store {
        id: UID,
        game_id: ID,
        potency: u64,
    }

    /// Enemy to fight
    public struct Boar has key, store {
        id: UID,
        game_id: ID,
        health: u64,
        strength: u64,
    }

    /// Game state (shared object)
    public struct Game has key {
        id: UID,
        payments: Balance<SUI>,
    }

    const MAX_HP: u64 = 1000;
    const MAX_MAGIC: u64 = 10;
    const MIN_SWORD_COST: u64 = 100;

    /// Create a sword - payment determines magic level
    public fun new_sword(
        game: &mut Game,
        payment: Coin<SUI>,
        ctx: &mut TxContext
    ): Sword {
        let value = payment.value();
        assert!(value >= MIN_SWORD_COST, EInsufficientFunds);

        coin::put(&mut game.payments, payment);

        let magic = (value - MIN_SWORD_COST) / MIN_SWORD_COST;
        Sword {
            id: object::new(ctx),
            magic: magic.min(MAX_MAGIC),
            strength: 1,
            game_id: object::id(game),
        }
    }

    /// Create a hero with a sword
    public fun new_hero(sword: Sword, ctx: &mut TxContext): Hero {
        Hero {
            id: object::new(ctx),
            game_id: sword.game_id,
            health: 100,
            experience: 0,
            sword: option::some(sword),
        }
    }

    /// Heal hero with potion
    public fun heal(hero: &mut Hero, potion: Potion) {
        let Potion { id, potency, game_id } = potion;
        id.delete();

        assert!(hero.game_id == game_id, EWrongGame);
        hero.health = (hero.health + potency).min(MAX_HP);
    }

    /// Equip sword to hero
    public fun equip(hero: &mut Hero, sword: Sword) {
        assert!(hero.sword.is_none(), EAlreadyEquipped);
        hero.sword.fill(sword);
    }

    /// Remove sword from hero
    public fun unequip(hero: &mut Hero): Sword {
        assert!(hero.sword.is_some(), ENotEquipped);
        option::extract(&mut hero.sword)
    }
}

Object Transfer Patterns

Direct Transfer

public fun transfer_nft(nft: NFT, recipient: address) {
    transfer::public_transfer(nft, recipient);
}

Transfer with Custom Logic

public fun transfer_with_fee(
    nft: NFT,
    recipient: address,
    fee: Coin<SUI>,
    fee_collector: address,
) {
    // Collect fee
    transfer::public_transfer(fee, fee_collector);
    // Transfer NFT
    transfer::public_transfer(nft, recipient);
}

Freeze Object

Make an object immutable:

public fun create_immutable_config(ctx: &mut TxContext) {
    let config = Config {
        id: object::new(ctx),
        value: 100,
    };
    transfer::public_freeze_object(config);
}

Object Deletion

Objects without drop must be explicitly deleted:

public fun burn_nft(nft: NFT) {
    let NFT { id, name: _, description: _, url: _ } = nft;
    object::delete(id);
}

Dynamic Fields

Attach data to objects dynamically:

use sui::dynamic_field as df;

public struct Container has key {
    id: UID,
}

public fun add_field(
    container: &mut Container,
    key: vector<u8>,
    value: u64,
) {
    df::add(&mut container.id, key, value);
}

public fun get_field(container: &Container, key: vector<u8>): &u64 {
    df::borrow(&container.id, key)
}

public fun remove_field(
    container: &mut Container,
    key: vector<u8>,
): u64 {
    df::remove(&mut container.id, key)
}

Object Display

Define how objects appear in wallets and explorers:

use sui::display;
use sui::package;

public struct NFT has key, store {
    id: UID,
    name: String,
    image_url: String,
}

public struct WITNESS has drop {}

fun init(witness: WITNESS, ctx: &mut TxContext) {
    let keys = vector[
        b"name".to_string(),
        b"image_url".to_string(),
        b"description".to_string(),
    ];

    let values = vector[
        b"{name}".to_string(),
        b"{image_url}".to_string(),
        b"A unique NFT".to_string(),
    ];

    let publisher = package::claim(witness, ctx);
    let mut display = display::new_with_fields<NFT>(
        &publisher, keys, values, ctx
    );
    display::update_version(&mut display);

    transfer::public_transfer(publisher, ctx.sender());
    transfer::public_transfer(display, ctx.sender());
}

Best Practices

1. Use descriptive struct names

// Good
public struct UserProfile has key { /* ... */ }
public struct GameAsset has key, store { /* ... */ }

// Avoid
public struct Data has key { /* ... */ }
public struct Object has key { /* ... */ }

2. Choose abilities carefully

// Soulbound (cannot transfer or store)
public struct Achievement has key {
    id: UID,
    owner: address,
}

// Tradeable
public struct TradingCard has key, store {
    id: UID,
    rarity: u8,
}

public fun use_item(hero: &mut Hero, item: Item) {
    // Ensure item belongs to same game
    assert!(hero.game_id == item.game_id, EWrongGame);
    // Use item...
}

4. Clean up resources

public fun consume_potion(potion: Potion): u64 {
    let Potion { id, potency, game_id: _ } = potion;
    object::delete(id);
    potency
}

5. Document object lifecycle

/// Creates a new quest.
/// The quest must be completed with `complete_quest` or
/// cancelled with `cancel_quest` before it can be deleted.
public fun create_quest(/* ... */) -> Quest {
    // ...
}

Getting Started

Move Development

Client Integration

Advanced Topics

Examples

Creating Custom Objects

Object Basics

Minimal Object

Object Abilities

The Four Abilities

Common Ability Combinations

Object Types

Owned Objects

Nested Objects

Objects with Options

Real-World Example: Game Characters

Object Transfer Patterns

Direct Transfer

Transfer with Custom Logic

Freeze Object

Object Deletion

Dynamic Fields

Object Display

Best Practices

1. Use descriptive struct names

2. Choose abilities carefully

4. Clean up resources

5. Document object lifecycle

Next Steps

​Object Basics

​Minimal Object

​Object Abilities

​The Four Abilities

​Common Ability Combinations

​Object Types

​Owned Objects

​Nested Objects

​Objects with Options

​Real-World Example: Game Characters

​Object Transfer Patterns

​Direct Transfer

​Transfer with Custom Logic

​Freeze Object

​Object Deletion

​Dynamic Fields

​Object Display

​Best Practices

​1. Use descriptive struct names

​2. Choose abilities carefully

​3. Validate related objects

​4. Clean up resources

​5. Document object lifecycle

​Next Steps

Object Basics

Minimal Object

Object Abilities

The Four Abilities

Common Ability Combinations

Object Types

Owned Objects

Nested Objects

Objects with Options

Real-World Example: Game Characters

Object Transfer Patterns

Direct Transfer

Transfer with Custom Logic

Freeze Object

Object Deletion

Dynamic Fields

Object Display

Best Practices

1. Use descriptive struct names

2. Choose abilities carefully

3. Validate related objects

4. Clean up resources

5. Document object lifecycle

Next Steps