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Macros in Scala 3

Tutorial

Language

    Introduction

    This tutorial covers all the features involved in writing macros in Scala 3.

    The metaprogramming API of Scala 3 is designed in layers to gradually support different levels of use-cases. Each successive layer exposes additional abstractions and offers more fine-grained control.

    • As a starting point, the new inline feature allows some abstractions (values and methods) to be marked as statically reducible. It provides the entry point for macros and other metaprogramming utilities.

    • Compile-time operations offer additional metaprogramming utilities that can be used within inline methods (for example to improve error reporting), without having to define a macro.

    • Starting from inline methods, macros are programs that explicitly operate on programs.

      • Macros can be defined in terms of a high-level API of quoted expressions, that admits simple construction and deconstruction of programs expressions.

      • Macros can also be defined in terms of a more low-level API of Reflection, that allows detailed inspection of programs.

    The tutorial uses the API of Scala 3.0.0-M3. The API had many small changes in this revision.

    🚧 We are still in the process of writing the tutorial. You can help us 🚧

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