Appendix D - The Cairo Prelude


The Cairo prelude is a collection of commonly used modules, functions, data types, and traits that are automatically brought into scope of every module in a Cairo crate without needing explicit import statements. Cairo's prelude provides the basic building blocks developers need to start Cairo programs and writing smart contracts.

The core library prelude is defined in the lib.cairo file of the corelib crate and contains Cairo's primitive data types, traits, operators, and utility functions. This includes:

  • Data types: integers, bools, arrays, dicts, etc.
  • Traits: behaviors for arithmetic, comparison, and serialization operations
  • Operators: arithmetic, logical, bitwise
  • Utility functions - helpers for arrays, maps, boxing, etc.

The core library prelude delivers the fundamental programming constructs and operations needed for basic Cairo programs, without requiring the explicit import of elements. Since the core library prelude is automatically imported, its contents are available for use in any Cairo crate without explicit imports. This prevents repetition and provides a better devX. This is what allows you to use ArrayTrait::append() or the Default trait without bringing them explicitly into scope.

You can choose which prelude to use. For example, adding edition = "2023_11" in the Scarb.toml configuration file will load the prelude from November 2023. Note that when you create a new project using scarb new command, the Scarb.toml file will automatically include edition = "2023_11".

The compiler currently exposes 2 different versions of the prelude:

  • A general version, with a lot of traits that are made available, corresponding to edition = "2023_01".
  • A restricted version, including the most essential traits needed for general Cairo programming, corresponding to edition = 2023_11.