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Module 0x2::balance

A storable handler for Balances in general. Is used in the Coin module to allow balance operations and can be used to implement custom coins with Supply and Balances.

use 0x2::tx_context;

Struct Supply​

A Supply of T. Used for minting and burning. Wrapped into a TreasuryCap in the Coin module.

struct Supply<T> has store
Fields
value: u64

Struct Balance​

Storable balance - an inner struct of a Coin type. Can be used to store coins which don't need the key ability.

struct Balance<T> has store
Fields
value: u64

Constants​

Sender is not @0x0 the system address.

const ENotSystemAddress: u64 = 3;

For when trying to destroy a non-zero balance.

const ENonZero: u64 = 0;

For when trying to withdraw more than there is.

const ENotEnough: u64 = 2;

For when an overflow is happening on Supply operations.

const EOverflow: u64 = 1;

Function value​

Get the amount stored in a Balance.

public fun value<T>(self: &balance::Balance<T>): u64
Implementation
public fun value<T>(self: &Balance<T>): u64 {
    self.value
}

Function supply_value​

Get the Supply value.

public fun supply_value<T>(supply: &balance::Supply<T>): u64
Implementation
public fun supply_value<T>(supply: &Supply<T>): u64 {
    supply.value
}

Function create_supply​

Create a new supply for type T.

public fun create_supply<T: drop>(_: T): balance::Supply<T>
Implementation
public fun create_supply<T: drop>(_: T): Supply<T> {
    Supply { value: 0 }
}

Function increase_supply​

Increase supply by value and create a new Balance<T> with this value.

public fun increase_supply<T>(self: &mut balance::Supply<T>, value: u64): balance::Balance<T>
Implementation
public fun increase_supply<T>(self: &mut Supply<T>, value: u64): Balance<T> {
    assert!(value < (18446744073709551615u64 - self.value), EOverflow);
    self.value = self.value + value;
    Balance { value }
}

Function decrease_supply​

Burn a Balance and decrease Supply.

public fun decrease_supply<T>(self: &mut balance::Supply<T>, balance: balance::Balance<T>): u64
Implementation
public fun decrease_supply<T>(self: &mut Supply<T>, balance: Balance<T>): u64 {
    let Balance { value } = balance;
    assert!(self.value >= value, EOverflow);
    self.value = self.value - value;
    value
}

Function zero​

Create a zero Balance for type T.

public fun zero<T>(): balance::Balance<T>
Implementation
public fun zero<T>(): Balance<T> {
    Balance { value: 0 }
}

Function join​

Join two balances together.

public fun join<T>(self: &mut balance::Balance<T>, balance: balance::Balance<T>): u64
Implementation
public fun join<T>(self: &mut Balance<T>, balance: Balance<T>): u64 {
    let Balance { value } = balance;
    self.value = self.value + value;
    self.value
}

Function split​

Split a Balance and take a sub balance from it.

public fun split<T>(self: &mut balance::Balance<T>, value: u64): balance::Balance<T>
Implementation
public fun split<T>(self: &mut Balance<T>, value: u64): Balance<T> {
    assert!(self.value >= value, ENotEnough);
    self.value = self.value - value;
    Balance { value }
}

Function withdraw_all​

Withdraw all balance. After this the remaining balance must be 0.

public fun withdraw_all<T>(self: &mut balance::Balance<T>): balance::Balance<T>
Implementation
public fun withdraw_all<T>(self: &mut Balance<T>): Balance<T> {
    let value = self.value;
    split(self, value)
}

Function destroy_zero​

Destroy a zero Balance.

public fun destroy_zero<T>(balance: balance::Balance<T>)
Implementation
public fun destroy_zero<T>(balance: Balance<T>) {
    assert!(balance.value == 0, ENonZero);
    let Balance { value: _ } = balance;
}

Function create_staking_rewards​

CAUTION: this function creates a Balance without increasing the supply. It should only be called by the epoch change system txn to create staking rewards, and nowhere else.

fun create_staking_rewards<T>(value: u64, ctx: &tx_context::TxContext): balance::Balance<T>
Implementation
fun create_staking_rewards<T>(value: u64, ctx: &TxContext): Balance<T> {
    assert!(ctx.sender() == @0x0, ENotSystemAddress);
    Balance { value }
}

Function destroy_storage_rebates​

CAUTION: this function destroys a Balance without decreasing the supply. It should only be called by the epoch change system txn to destroy storage rebates, and nowhere else.

fun destroy_storage_rebates<T>(self: balance::Balance<T>, ctx: &tx_context::TxContext)
Implementation
fun destroy_storage_rebates<T>(self: Balance<T>, ctx: &TxContext) {
    assert!(ctx.sender() == @0x0, ENotSystemAddress);
    let Balance { value: _ } = self;
}

Function destroy_supply​

Destroy a Supply preventing any further minting and burning.

public(friend) fun destroy_supply<T>(self: balance::Supply<T>): u64
Implementation
public(package) fun destroy_supply<T>(self: Supply<T>): u64 {
    let Supply { value } = self;
    value
}