# Assets Module
A simple, secure module for dealing with fungible assets.
## Overview
The Assets module provides functionality for asset management of fungible asset classes with a fixed supply, including:
* Asset Issuance
* Asset Transfer
* Asset Destruction
To use it in your runtime, you need to implement the assets
[`assets::Config`](https://docs.rs/pallet-assets/latest/pallet_assets/pallet/trait.Config.html).
The supported dispatchable functions are documented in the
[`assets::Call`](https://docs.rs/pallet-assets/latest/pallet_assets/pallet/enum.Call.html) enum.
### Terminology
* **Asset issuance:** The creation of a new asset, whose total supply will belong to the account that issues the asset.
* **Asset transfer:** The action of transferring assets from one account to another.
* **Asset destruction:** The process of an account removing its entire holding of an asset.
* **Fungible asset:** An asset whose units are interchangeable.
* **Non-fungible asset:** An asset for which each unit has unique characteristics.
### Goals
The assets system in Substrate is designed to make the following possible:
* Issue a unique asset to its creator's account.
* Move assets between accounts.
* Remove an account's balance of an asset when requested by that account's owner and update the asset's total supply.
## Interface
### Dispatchable Functions
* `issue` - Issues the total supply of a new fungible asset to the account of the caller of the function.
* `transfer` - Transfers an `amount` of units of fungible asset `id` from the balance of the function caller's account
(`origin`) to a `target` account.
* `destroy` - Destroys the entire holding of a fungible asset `id` associated with the account that called the function.
Please refer to the [`Call`](https://docs.rs/pallet-assets/latest/pallet_assets/enum.Call.html) enum and its associated
variants for documentation on each function.
### Public Functions
* `balance` - Get the asset `id` balance of `who`.
* `total_supply` - Get the total supply of an asset `id`.
Please refer to the [`Pallet`](https://docs.rs/pallet-assets/latest/pallet_assets/pallet/struct.Pallet.html) struct for
details on publicly available functions.
## Usage
The following example shows how to use the Assets module in your runtime by exposing public functions to:
* Issue a new fungible asset for a token distribution event (airdrop).
* Query the fungible asset holding balance of an account.
* Query the total supply of a fungible asset that has been issued.
### Prerequisites
Import the Assets module and types and derive your runtime's configuration traits from the Assets module trait.
### Simple Code Snippet
```rust
use pallet_assets as assets;
use sp_runtime::ArithmeticError;
#[frame_support::pallet]
pub mod pallet {
use super::*;
use frame_support::pallet_prelude::*;
use frame_system::pallet_prelude::*;
#[pallet::pallet]
pub struct Pallet<T>(_);
#[pallet::config]
pub trait Config: frame_system::Config + assets::Config {}
#[pallet::call]
impl<T: Config> Pallet<T> {
pub fn issue_token_airdrop(origin: OriginFor<T>) -> DispatchResult {
let sender = ensure_signed(origin)?;
const ACCOUNT_ALICE: u64 = 1;
const ACCOUNT_BOB: u64 = 2;
const COUNT_AIRDROP_RECIPIENTS: u64 = 2;
const TOKENS_FIXED_SUPPLY: u64 = 100;
ensure!(!COUNT_AIRDROP_RECIPIENTS.is_zero(), ArithmeticError::DivisionByZero);
let asset_id = Self::next_asset_id();
<NextAssetId<T>>::mutate(|asset_id| *asset_id += 1);
<Balances<T>>::insert((asset_id, &ACCOUNT_ALICE), TOKENS_FIXED_SUPPLY / COUNT_AIRDROP_RECIPIENTS);
<Balances<T>>::insert((asset_id, &ACCOUNT_BOB), TOKENS_FIXED_SUPPLY / COUNT_AIRDROP_RECIPIENTS);
<TotalSupply<T>>::insert(asset_id, TOKENS_FIXED_SUPPLY);
Self::deposit_event(Event::Issued(asset_id, sender, TOKENS_FIXED_SUPPLY));
Ok(())
}
}
}
```
## Assumptions
Below are assumptions that must be held when using this module. If any of them are violated, the behavior of this
module is undefined.
* The total count of assets should be less than `Config::AssetId::max_value()`.
## Related Modules
* [`System`](https://docs.rs/frame-system/latest/frame_system/)
* [`Support`](https://docs.rs/frame-support/latest/frame_support/)
License: Apache-2.0