Standard Library

Similar to Rust, Sway comes with its own standard library.

The Sway Standard Library is the foundation of portable Sway software, a set of minimal shared abstractions for the broader Sway ecosystem. It offers core types, like Result<T, E> and Option<T>, library-defined operations on language primitives, native asset management, blockchain contextual operations, access control, storage management, and support for types from other VMs, among many other things.

The entire Sway standard library is a Forc project called std, and is available directly here: https://github.com/FuelLabs/sway/tree/master/sway-lib-std (navigate to the appropriate tagged release if the latest master is not compatible).

Using the Standard Library

The standard library is made implicitly available to all Forc projects created using forc new. In other words, it is not required to manually specify std as an explicit dependency. Forc will automatically use the version of std that matches its version.

Importing items from the standard library can be done using the use keyword, just as importing items from any Sway project. For example:

use std::storage::StorageVec;

This imports the StorageVec type into the current namespace.

Standard Library Prelude

Sway comes with a variety of things in its standard library. However, if you had to manually import every single thing that you used, it would be very verbose. But importing a lot of things that a program never uses isn't good either. A balance needs to be struck.

The prelude is the list of things that Sway automatically imports into every Sway program. It's kept as small as possible, and is focused on things which are used in almost every single Sway program.

The current version of the prelude lives in std::prelude, and re-exports the following:

• std::address::Address, a wrapper around the b256 type representing a wallet address.
• std::contract_id::ContractId, a wrapper around the b256 type representing the ID of a contract.
• std::identity::Identity, an enum with two possible variants: Address: Address and ContractId: ContractId.
• std::vec::Vec, a growable, heap-allocated vector.
• std::storage::StorageMap, a key-value mapping in contract storage.
• std::option::Option, an enum which expresses the presence or absence of a value.
• std::result::Result, an enum for functions that may succeed or fail.
• std::assert::assert, a function that reverts the VM if the condition provided to it is false.
• std::assert::assert_eq, a function that reverts the VM and logs its two inputs v1 and v2 if the condition v1 == v2 is false.
• std::revert::require, a function that reverts the VM and logs a given value if the condition provided to it is false.
• std::revert::revert, a function that reverts the VM.
• std::logging::log, a function that logs arbitrary stack types.