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Module 0x3::storage_fund

use 0x2::balance;
use 0x2::iota;

Struct StorageFundV1​

Struct representing the storage fund, containing two Balances:

  • total_object_storage_rebates has the invariant that it's the sum of storage_rebate of all objects currently stored on-chain. To maintain this invariant, the only inflow of this balance is storage charges collected from transactions, and the only outflow is storage rebates of transactions, including both the portion refunded to the transaction senders as well as the non-refundable portion taken out and put into non_refundable_balance.
  • non_refundable_balance contains any remaining inflow of the storage fund that should not be taken out of the fund.
struct StorageFundV1 has store
Fields
total_object_storage_rebates: balance::Balance<iota::IOTA>
non_refundable_balance: balance::Balance<iota::IOTA>

Function new​

Called by iota_system at genesis time.

public(friend) fun new(initial_fund: balance::Balance<iota::IOTA>): storage_fund::StorageFundV1
Implementation
public(package) fun new(initial_fund: Balance<IOTA>) : StorageFundV1 {
StorageFundV1 {
// At the beginning there's no object in the storage yet
total_object_storage_rebates: balance::zero(),
non_refundable_balance: initial_fund,
}
}

Function advance_epoch​

Called by iota_system at epoch change times to process the inflows and outflows of storage fund.

public(friend) fun advance_epoch(self: &mut storage_fund::StorageFundV1, storage_charges: balance::Balance<iota::IOTA>, storage_rebate_amount: u64, non_refundable_storage_fee_amount: u64): balance::Balance<iota::IOTA>
Implementation
public(package) fun advance_epoch(
self: &mut StorageFundV1,
storage_charges: Balance<IOTA>,
storage_rebate_amount: u64,
non_refundable_storage_fee_amount: u64,
) : Balance<IOTA> {
// The storage charges for the epoch come from the storage rebate of the new objects created
// and the new storage rebates of the objects modified during the epoch so we put the charges
// into total_object_storage_rebates.
self.total_object_storage_rebates.join(storage_charges);
// Split out the non-refundable portion of the storage rebate and put it into the non-refundable balance.
let non_refundable_storage_fee = self.total_object_storage_rebates.split(non_refundable_storage_fee_amount);
self.non_refundable_balance.join(non_refundable_storage_fee);
// storage_rebates include the already refunded rebates of deleted objects and old rebates of modified objects and
// should be taken out of the total_object_storage_rebates.
let storage_rebate = self.total_object_storage_rebates.split(storage_rebate_amount);
// The storage rebate has already been returned to individual transaction senders' gas coins
// so we return the balance to be burnt at the very end of epoch change.
storage_rebate
}

Function total_object_storage_rebates​

public fun total_object_storage_rebates(self: &storage_fund::StorageFundV1): u64
Implementation
public fun total_object_storage_rebates(self: &StorageFundV1): u64 {
self.total_object_storage_rebates.value()
}

Function total_balance​

public fun total_balance(self: &storage_fund::StorageFundV1): u64
Implementation
public fun total_balance(self: &StorageFundV1): u64 {
self.total_object_storage_rebates.value() + self.non_refundable_balance.value()
}