Abi

Selects the calling convention a function is compiled with — the contract for how arguments, the return value, and the stack are arranged. Most code never needs it: Rux uses the right convention for the target automatically. Reach for #Abi at a foreign boundary that must follow a specific ABI regardless of the platform default.

Syntax

#Abi(.SysV)
func FastPath(a: int32, b: int32) -> int32 {
    return a + b;
}

The argument is one of three ABI variants:

Without #Abi, a function uses the platform's default convention. #Abi(.C) is the form to use when calling into or being called from C.

On extern and asm

#Abi is most useful on declarations that cross a language boundary — extern functions and asm func bodies — where the ABI must match exactly what the other side expects:

#Abi(.Win64)
asm func Add(a: int32, b: int32) -> int32 {
    mov eax, ecx      // Win64: first two integer args in ecx/edx
    add eax, edx
    ret
}

See Also

• Assembler Functions — where a fixed ABI matters most
• extern Declarations — foreign functions that follow a C ABI
• Attributes — the full attribute set