size-of-option

option.rs

use std::mem::size_of;

#[repr(C)]
pub enum POption<T> {
	PSome(T),
}

#[repr(C)]
pub struct SOption<T>(T);

#[repr(C)]
struct S
{
	mem1: i32,
	o1: Option<i32>,
	o2: Option<*const i32>,
	o3: Option<extern "system" fn (i32, i32) -> i32>,
}

extern "system" fn func1(arg: *const i32) -> i32 {
	unsafe { *arg + 1 }
}

extern "system" fn func2(arg: &i32) -> i32 {
	*arg + 1
}

extern "system" fn func3(arg: Option<i32>) -> i32 {
	if let Some(x) = arg {
		x + 1
	} else {
		-8
	}
}

extern "system" fn func4(arg: Option<*const i32>) -> i32 {
	if let Some(x) = arg {
		unsafe { *x + 1 }
	} else {
		-8
	}
}

extern "system" fn func5(arg: &S) -> i32 {
	let mut ret = 0;

	ret += arg.mem1;
	if let Some(x) = arg.o1 {
		ret += x;
	}
	if let Some(x) = arg.o2 {
		ret += unsafe { *x };
	}

	return ret;
}


fn main()
{

	println!("sizeof S {}", size_of::<S>());
	println!("sizeof Option<i32> {}", size_of::<Option<i32>>());
	println!("sizeof Option<&i32> {}", size_of::<Option<&i32>>());
	println!("sizeof Option<*i32> {}", size_of::<Option<*const i32>>());
	println!("sizeof Option<fn> {}\n", size_of::<Option<extern "system" fn () -> i32>>());

	println!("sizeof POption<i32> {}", size_of::<POption<i32>>());
	println!("sizeof POption<&i32> {}", size_of::<POption<&i32>>());
	println!("sizeof POption<*i32> {}", size_of::<POption<*const i32>>());
	println!("sizeof POption<fn> {}\n", size_of::<POption<extern "system" fn () -> i32>>());

	println!("sizeof SOption<i32> {}", size_of::<SOption<i32>>());
	println!("sizeof SOption<&i32> {}", size_of::<SOption<&i32>>());
	println!("sizeof SOption<*i32> {}", size_of::<SOption<*const i32>>());
	println!("sizeof SOption<fn> {}\n", size_of::<SOption<extern "system" fn () -> i32>>());
}