# Module `iota::bag` A bag is a heterogeneous map-like collection. The collection is similar to iota::table in that its keys and values are not stored within the Bag value, but instead are stored using IOTA's object system. The Bag struct acts only as a handle into the object system to retrieve those keys and values. Note that this means that Bag values with exactly the same key-value mapping will not be equal, with ==, at runtime. For example ``` let bag1 = bag::new(); let bag2 = bag::new(); bag::add(&mut bag1, 0, false); bag::add(&mut bag1, 1, true); bag::add(&mut bag2, 0, false); bag::add(&mut bag2, 1, true); // bag1 does not equal bag2, despite having the same entries assert!(&bag1 != &bag2); ``` At it's core, iota::bag is a wrapper around UID that allows for access to iota::dynamic_field while preventing accidentally stranding field values. A UID can be deleted, even if it has dynamic fields associated with it, but a bag, on the other hand, must be empty to be destroyed. - [Struct `Bag`](#iota_bag_Bag) - [Constants](#@Constants_0) - [Function `new`](#iota_bag_new) - [Function `add`](#iota_bag_add) - [Function `borrow`](#iota_bag_borrow) - [Function `borrow_mut`](#iota_bag_borrow_mut) - [Function `remove`](#iota_bag_remove) - [Function `contains`](#iota_bag_contains) - [Function `contains_with_type`](#iota_bag_contains_with_type) - [Function `length`](#iota_bag_length) - [Function `is_empty`](#iota_bag_is_empty) - [Function `destroy_empty`](#iota_bag_destroy_empty)

use iota::address;
use iota::dynamic_field;
use iota::hex;
use iota::object;
use iota::tx_context;
use std::ascii;
use std::bcs;
use std::option;
use std::string;
use std::vector;

## Struct `Bag`

public struct Bag has key, store

Fields

id: iota::object::UID: the ID of this bag
size: u64: the number of key-value pairs in the bag

## Constants

const EBagNotEmpty: u64 = 0;

## Function `new` Creates a new, empty bag

public fun new(ctx: &mut iota::tx_context::TxContext): iota::bag::Bag

Implementation

public fun new(ctx: &mut TxContext): Bag {
    Bag {
        id: object::new(ctx),
        size: 0,
    }
}

## Function `add` Adds a key-value pair to the bag bag: &mut Bag Aborts with iota::dynamic_field::EFieldAlreadyExists if the bag already has an entry with that key k: K.

public fun add<K: copy, drop, store, V: store>(bag: &mut iota::bag::Bag, k: K, v: V)

Implementation

public fun add<K: copy + drop + store, V: store>(bag: &mut Bag, k: K, v: V) {
    field::add(&mut bag.id, k, v);
    bag.size = bag.size + 1;
}

## Function `borrow` Immutable borrows the value associated with the key in the bag bag: &Bag. Aborts with iota::dynamic_field::EFieldDoesNotExist if the bag does not have an entry with that key k: K. Aborts with iota::dynamic_field::EFieldTypeMismatch if the bag has an entry for the key, but the value does not have the specified type.

public fun borrow<K: copy, drop, store, V: store>(bag: &iota::bag::Bag, k: K): &V

Implementation

public fun borrow<K: copy + drop + store, V: store>(bag: &Bag, k: K): &V {
    field::borrow(&bag.id, k)
}

## Function `borrow_mut` Mutably borrows the value associated with the key in the bag bag: &mut Bag. Aborts with iota::dynamic_field::EFieldDoesNotExist if the bag does not have an entry with that key k: K. Aborts with iota::dynamic_field::EFieldTypeMismatch if the bag has an entry for the key, but the value does not have the specified type.

public fun borrow_mut<K: copy, drop, store, V: store>(bag: &mut iota::bag::Bag, k: K): &mut V

Implementation

public fun borrow_mut<K: copy + drop + store, V: store>(bag: &mut Bag, k: K): &mut V {
    field::borrow_mut(&mut bag.id, k)
}

## Function `remove` Mutably borrows the key-value pair in the bag bag: &mut Bag and returns the value. Aborts with iota::dynamic_field::EFieldDoesNotExist if the bag does not have an entry with that key k: K. Aborts with iota::dynamic_field::EFieldTypeMismatch if the bag has an entry for the key, but the value does not have the specified type.

public fun remove<K: copy, drop, store, V: store>(bag: &mut iota::bag::Bag, k: K): V

Implementation

public fun remove<K: copy + drop + store, V: store>(bag: &mut Bag, k: K): V {
    let v = field::remove(&mut bag.id, k);
    bag.size = bag.size - 1;
    v
}

## Function `contains` Returns true iff there is an value associated with the key k: K in the bag bag: &Bag

public fun contains<K: copy, drop, store>(bag: &iota::bag::Bag, k: K): bool

Implementation

public fun contains<K: copy + drop + store>(bag: &Bag, k: K): bool {
    field::exists_<K>(&bag.id, k)
}

## Function `contains_with_type` Returns true iff there is an value associated with the key k: K in the bag bag: &Bag with an assigned value of type V

public fun contains_with_type<K: copy, drop, store, V: store>(bag: &iota::bag::Bag, k: K): bool

Implementation

public fun contains_with_type<K: copy + drop + store, V: store>(bag: &Bag, k: K): bool {
    field::exists_with_type<K, V>(&bag.id, k)
}

## Function `length` Returns the size of the bag, the number of key-value pairs

public fun length(bag: &iota::bag::Bag): u64

Implementation

public fun length(bag: &Bag): u64 {
    bag.size
}

## Function `is_empty` Returns true iff the bag is empty (if length returns 0)

public fun is_empty(bag: &iota::bag::Bag): bool

Implementation

public fun is_empty(bag: &Bag): bool {
    bag.size == 0
}

## Function `destroy_empty` Destroys an empty bag Aborts with EBagNotEmpty if the bag still contains values

public fun destroy_empty(bag: iota::bag::Bag)

Implementation

public fun destroy_empty(bag: Bag) {
    let Bag { id, size } = bag;
    assert!(size == 0, EBagNotEmpty);
    id.delete()
}