What is macro?

💡 Macro is a feature that generates code during compilation. Unlike macros in C, which work like “find and replace”, Swift macros are type-safe and context aware, making them powerful tools reducing boilerplate code.

Two types of macros

  • attached - use @ prefix, tied to a declaration adding extra logic to it, like: @Test, @Model, @Observable
  • freestanding - use # prefix, standalone code that can be invoked independently as a part of the code, like #expect, #Predicate, #warning

Example of attached macro ⤵️

@Test func addition() { // tied to the declaration
    ...
}

Example of freestanding macro ⤵️

@Test func addition() {
    #require(1 + 2 == 3) // not attached to a declaration
}

Bonus

It’s possible to expand macros, especially those defined by you, and check their implementation by right-clicking on a macro and selecting the “Expand Macro” option. ⤵️

Expanded_macro

Resources

Thanks for reading. đź“–

I hope you found it useful!

If you enjoy the topic don’t forget to follow me on one of my social media - LinkedIn, X, Mastodon, Bluesky or via RSS feed to keep up to speed. 🚀