macros

In Swift, there isn't a preprocessor and therefore no concept of macros as you might know them from languages like C or C++. Swift aims to be simple and clear, and it tries to reduce the amount of hidden behavior or code transformations. Macros can often lead to hard-to-understand code and tricky debugging scenarios, which is why Swift has mostly avoided them.

However, you can use compile-time directives that offer similar functionalities in some cases:

Conditional Compilation

You can use conditional compilation blocks defined by #if, #else, #elseif, and #endif to conditionally include code. The most common use case is for platform checks.

#if os(iOS)
   // iOS specific code
#elseif os(macOS)
   // macOS specific code
#else
   // Code for other platforms
#endif

Debug and Release Builds

You can use conditional compilation to distinguish between debug and release builds.

#if DEBUG
   print("This is a debug build!")
#else
   print("This is a release build!")
#endif

Custom Compilation Flags

You can also define your own compilation conditions by passing flags to the Swift compiler using the -D flag. For example, to define a custom EXPERIMENTAL flag, you could compile your Swift code with swiftc -D EXPERIMENTAL. You could then use this in your code like so:

#if EXPERIMENTAL
   print("Experimental feature enabled")
#endif

Function Inlining and Optimization Hints

In Swift, you can provide hints to the compiler about function inlining using @inlinable and @inline(__always)attributes. These aren't macros, but they do influence the compilation process.

@inlinable func performFastOperation() {
   // code
}

or

@inline(__always) func superFastInlineOperation() {
   // code
}

Other Directives

Swift also supports other compiler directives like #warning and #error for emitting warnings and errors during compilation.

#warning("This is a warning message")
#error("This is an error message")

So, while Swift doesn't support macros in the traditional sense, it does offer various ways to achieve similar results through its type system, language features, and compiler directives.