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Capabilities

A capability is a design pattern that enables the authorization of specific actions with an object. For instance, the UpgradeCap is used to authorize the upgrading of packages. Another common example is the TreasuryCap, which grants the authority to manage treasury functions.

module examples::item {
    use std::string::String;

    /// Type representing the capability to create new `Item`s.
    public struct AdminCap has key { id: UID }

    /// Custom NFT-like type representing an item.
    public struct Item has key, store { id: UID, name: String }

    /// Module initializer, called once during the module's deployment.
    /// This function creates a single instance of `AdminCap` and assigns it to the publisher.
    fun init(ctx: &mut TxContext) {
        transfer::transfer(AdminCap {
            id: object::new(ctx)
        }, tx_context::sender(ctx))
    }

    /// Function to create a new `Item`. It requires `AdminCap` to authorize the action.
    public fun create_item(_: &AdminCap, name: String, ctx: &mut TxContext): Item {
        let item = Item {
            id: object::new(ctx),
            name,
        };
        item
    }
}

Question 1/2

What is a capability in the context of the Move language?