Unsafe & FFI

Unsafe Blocks

Sailfin’s safety guarantees can be bypassed in unsafe blocks for low-level operations:

unsafe {
    let ptr: raw *mut Int = raw_alloc(size);
    raw_write(ptr, 42);
    let value = raw_read(ptr);
    raw_free(ptr);
}

Extern Functions

Call C functions via extern declarations:

extern fn malloc(size: Int) -> raw *mut Byte;
extern fn free(ptr: raw *mut Byte);
extern fn strlen(s: raw *Byte) -> Int;

Raw Pointers

• raw *T — Raw immutable pointer
• raw *mut T — Raw mutable pointer
• opaque — Opaque foreign type

Safety Rules

• Raw pointer operations require unsafe blocks
• unsafe blocks cannot be used inside pure (no-effect) functions without explicit ![io]
• FFI calls are inherently unsafe — the compiler trusts extern declarations

FFI is parsed and partially implemented. Full extern support is planned for the native runtime migration. See Runtime ABI.