Extern

Extern declarations use external linkage: symbols resolve at link time by the system linker. Missing symbols fail the link step.

Functions

extern fn without a body declares an imported symbol. Calls use the C calling convention:

extern fn malloc(usize) *void;
extern fn free(*void);

fn main() {
  let ptr: *i32 = malloc(4);
  *ptr = 123;
  free(ptr);
}

extern fn with a body exports the symbol for native callers:

extern fn hello() {
  @println("hi from Zeen");
}

Varargs with ...:

extern fn printf([*]const char, ...);

Variables

extern let declares an imported global. Storage lives in native code, no value allowed:

extern let errno: i32;

Link

extern link appends native files after the compiled object in the link step:

extern link "helpers.c";

Object-only toolchains skip these sources with a warning.