Skip to main content

Module iota::borrow

A simple library that enables hot-potato-locked borrow mechanics.

With Programmable transactions, it is possible to borrow a value within a transaction, use it and put back in the end. Hot-potato Borrow makes sure the object is returned and was not swapped for another one.

use iota::address;
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 Referent​

An object wrapping a T and providing the borrow API.

public struct Referent<T: key, store> has store
Fields
id: address
value: std::option::Option<T>

Struct Borrow​

A hot potato making sure the object is put back once borrowed.

publicstructBorrow
Fields
ref: address
obj: iota::object::ID

Constants​

The Borrow does not match the Referent.

const EWrongBorrow: u64 = 0;

An attempt to swap the Referent.value with another object of the same type.

const EWrongValue: u64 = 1;

Function new​

Create a new Referent struct

public fun new<T: key, store>(value: T, ctx: &mut iota::tx_context::TxContext): iota::borrow::Referent<T>
Implementation
public fun new<T: key + store>(value: T, ctx: &mut TxContext): Referent<T> {
Referent {
id: tx_context::fresh_object_address(ctx),
value: option::some(value),
}
}

Function borrow​

Borrow the T from the Referent receiving the T and a Borrow hot potato.

public fun borrow<T: key, store>(self: &mut iota::borrow::Referent<T>): (T, iota::borrow::Borrow)
Implementation
public fun borrow<T: key + store>(self: &mut Referent<T>): (T, Borrow) {
let value = self.value.extract();
let id = object::id(&value);
(
value,
Borrow {
ref: self.id,
obj: id,
},
)
}

Function put_back​

Put an object and the Borrow hot potato back.

public fun put_back<T: key, store>(self: &mut iota::borrow::Referent<T>, value: T, borrow: iota::borrow::Borrow)
Implementation
public fun put_back<T: key + store>(self: &mut Referent<T>, value: T, borrow: Borrow) {
let Borrow { ref, obj } = borrow;
assert!(object::id(&value) == obj, EWrongValue);
assert!(self.id == ref, EWrongBorrow);
self.value.fill(value);
}

Function destroy​

Unpack the Referent struct and return the value.

public fun destroy<T: key, store>(self: iota::borrow::Referent<T>): T
Implementation
public fun destroy<T: key + store>(self: Referent<T>): T {
let Referent { id: _, value } = self;
value.destroy_some()
}