The following documentation provides reasoning and examples for functions and constants found in openzeppelin::utils and openzeppelin::tests::utils.

Expect this module to evolve (as it has already done).

Core utilities


use openzeppelin::utils;

Module containing core utilities of the library.


try_selector_with_fallback(target: ContractAddress, selector: felt252, fallback: felt252, args: Span<felt252>) → SyscallResult<Span<felt252>> function

Tries to call a given selector on a given contract, and if it fails, tries to call a fallback selector.

It was designed for falling back to the camelCase selector for backward compatibility in the case of a failure of the snake_case selector.

Returns a SyscallResult with the result of the successful call.

Note that:

  • If the first call succeeds, the second call is not attempted.

  • If the first call fails with an error different than ENTRYPOINT_NOT_FOUND, the error is returned without falling back to the second selector.

  • If the first call fails with ENTRYPOINT_NOT_FOUND, the second call is attempted, and if it fails its error is returned.

The fallback mechanism won’t work on live chains (mainnet or testnets) until they implement panic handling in their runtime.


UnwrapAndCast trait

Trait for exposing an unwrap_and_cast function to SyscallResult objects. This may be useful when unwrapping a syscall result to a type implementing the Serde trait, and you want to avoid the boilerplate of casting and unwrapping the result multiple times.

Usage example:

use openzeppelin::utils::selectors;
use openzeppelin::utils::UnwrapAndCast;

fn call_and_cast_to_bool(target: ContractAddress, args: Span<felt252>) -> bool {
        target, selectors::has_role, selectors::hasRole, args

fn call_and_cast_to_felt252(target: ContractAddress, args: Span<felt252>) -> felt252 {
        target, selectors::get_role_admin, selectors::getRoleAdmin, args

Note that it can be automatically casted to any type implementing the Serde trait.

Inner modules

cryptography module

selectors module

serde module


use openzeppelin::utils::cryptography;

Module containing utilities related to cryptography.

Inner modules

Inner modules


use openzeppelin::utils::selectors;

Module containing constants matching multiple selectors used through the library. To see the full list of selectors, see selectors.cairo.


use openzeppelin::utils::serde;

Module containing utilities related to serialization and deserialization of Cairo data structures.



SerializedAppend trait

Importing this trait allows the ability to append a serialized representation of a Cairo data structure already implementing the Serde trait to a felt252 buffer.

Usage example:

use openzeppelin::utils::serde::SerializedAppend;
use starknet::ContractAddress;

fn to_calldata(recipient: ContractAddress, amount: u256) -> Array<felt252> {
    let mut calldata = array![];

Note that the append_serde method is automatically available for arrays of felts, and it accepts any data structure that implements the Serde trait.



use openzeppelin::utils::cryptography::nonces::NoncesComponent;

Simple component for managing nonces.

Embeddable Implementations
Internal Implementations

Embeddable functions

nonces(self: @ContractState, owner: ContractAddress) → felt252 external

Returns the next unused nonce for an owner.

Internal functions

use_nonce(ref self: ComponentState, owner: ContractAddress) → felt252 internal

Consumes a nonce, returns the current value, and increments nonce.

For each account, the nonce has an initial value of 0, can only be incremented by one, and cannot be decremented or reset. This guarantees that the nonce never overflows.

use_checked_nonce(ref self: ComponentState, owner: ContractAddress, nonce: felt252) → felt252 internal

Same as use_nonce but checking that nonce is the next valid one for owner.


use openzeppelin::utils::snip12;

Supports on-chain generation of message hashes compliant with SNIP12.

For a full walkthrough on how to use this module, see the SNIP12 and Typed Messages guide.

Test utilities


use openzeppelin::tests::utils;

Module containing utilities for testing the library.


deploy(contract_class_hash: felt252, calldata: Array<felt252>) → ContractAddress function

Uses the deploy_syscall to deploy an instance of the contract given the class hash and the calldata.

The contract_address_salt is always set to zero, and deploy_from_zero is set to false.

Usage example:

use openzeppelin::presets::Account;
use openzeppelin::tests::utils;
use starknet::ContractAddress;

const PUBKEY: felt252 = 'PUBKEY';

fn deploy_test_contract() -> ContractAddress {
    let calldata = array![PUBKEY];
    utils::deploy(Account::TEST_CLASS_HASH, calldata)

pop_log<T>(address: ContractAddress) → Option<T> function

Pops the earliest unpopped logged event for the contract as the requested type and checks that there’s no more keys or data left on the event, preventing unaccounted params.

Required traits for T:

  • Drop

  • starknet::Event


  • No extra data or keys are left on the raw event after deserialization.

This method doesn’t currently work for component events that are not flattened because an extra key is added, pushing the event ID key to the second position.

assert_indexed_keys<T>(event: T, expected_keys: Span<felt252>) function

Asserts that expected_keys exactly matches the indexed keys from event.

expected_keys must include all indexed event keys for event in the order that they’re defined.

If the event is not flattened, the first key will be the event member name e.g. selector!("EnumMemberName").

Required traits for T:

  • Drop

  • starknet::Event

assert_no_events_left(address: ContractAddress) function

Asserts that there are no more events left in the queue for the given address.

drop_event(address: ContractAddress) function

Removes an event from the queue for the given address.

If the queue is empty, this function won’t do anything.

Inner modules


use openzeppelin::tests::utils::constants;

Module containing constants that are repeatedly used among tests. To see the full list, see constants.cairo.