basic test

Author: BennoLossin

library/std/tests/field_projections/basic.rs

@@ -0,0 +1,35 @@
+#![allow(incomplete_features)]
+#![feature(field_projections)]
+
+use std::field::{Field, UnalignedField, field_of};
+use std::mem::offset_of;
+use std::ptr;
+
+pub struct Foo {
+    pub x: usize,
+    pub y: usize,
+    pub z: (usize, usize),
+}
+
+pub fn project_ref<F: Field>(r: &F::Base) -> &F::Type
+where
+    F::Type: Sized,
+{
+    unsafe { &*ptr::from_ref(r).byte_add(F::OFFSET).cast() }
+}
+
+#[test]
+fn foo() {
+    let foo = Foo { x: 42, y: 24, z: (43, 44) };
+    let x = project_ref::<field_of!(Foo, x)>(&foo);
+    let y = project_ref::<field_of!(Foo, y)>(&foo);
+    let z0 = project_ref::<field_of!(Foo, z.0)>(&foo);
+    let z1 = project_ref::<field_of!(Foo, z.1)>(&foo);
+    assert_eq!(*x, 42);
+    assert_eq!(*y, 24);
+    assert_eq!(<field_of!(Foo, x)>::OFFSET, offset_of!(Foo, x));
+    assert_eq!(*z0, 43);
+    assert_eq!(*z1, 44);
+}
+
+fn main() {}