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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 TASTy Reflection, that allows detailed inspection of programs.

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