light_clone 0.4.1

Compile-time enforcement for O(1) clone operations
Documentation 
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use light_clone::LightClone;
use std::sync::Arc;

#[derive(Clone, LightClone)]
struct PrimitiveStruct {
    a: i32,
    b: u64,
    c: f64,
    d: bool,
    e: char,
}

#[test]
fn test_basic_struct_with_primitives() {
    let s = PrimitiveStruct {
        a: 42,
        b: 100,
        c: 2.72,
        d: true,
        e: 'x',
    };

    let cloned = s.light_clone();
    assert_eq!(cloned.a, 42);
    assert_eq!(cloned.b, 100);
    assert!((cloned.c - 2.72).abs() < f64::EPSILON);
    assert!(cloned.d);
    assert_eq!(cloned.e, 'x');
}

#[test]
fn test_clone_and_light_clone_equivalent() {
    let s = PrimitiveStruct {
        a: 1,
        b: 2,
        c: 3.0,
        d: false,
        e: 'y',
    };

    let cloned_via_clone = s.clone();
    let cloned_via_lc = s.light_clone();
    assert_eq!(cloned_via_clone.a, cloned_via_lc.a);
    assert_eq!(cloned_via_clone.b, cloned_via_lc.b);
}

#[derive(Clone, LightClone)]
struct ArcFieldsStruct {
    name: Arc<str>,
    data: Arc<[u8]>,
    value: i32,
}

#[test]
fn test_struct_with_arc_fields() {
    let s = ArcFieldsStruct {
        name: Arc::from("hello"),
        data: Arc::from([1u8, 2, 3].as_slice()),
        value: 42,
    };

    let cloned = s.light_clone();
    assert_eq!(&*cloned.name, "hello");
    assert_eq!(&*cloned.data, &[1, 2, 3]);
    assert_eq!(cloned.value, 42);

    // Verify Arc is shared, not deep copied
    assert!(Arc::ptr_eq(&s.name, &cloned.name));
    assert!(Arc::ptr_eq(&s.data, &cloned.data));
}

#[test]
fn test_arc_strong_count_after_lc() {
    let s = ArcFieldsStruct {
        name: Arc::from("test"),
        data: Arc::from([1u8].as_slice()),
        value: 1,
    };

    assert_eq!(Arc::strong_count(&s.name), 1);
    let cloned = s.light_clone();
    assert_eq!(Arc::strong_count(&s.name), 2);
    assert_eq!(Arc::strong_count(&cloned.name), 2);
}

// Test: manual Clone impl + derived LightClone
struct ManualClone {
    value: i32,
}

impl Clone for ManualClone {
    fn clone(&self) -> Self {
        ManualClone { value: self.value }
    }
}

// We can manually implement LightClone for a type with manual Clone
impl LightClone for ManualClone {}

#[test]
fn test_manual_clone_with_light_clone() {
    let m = ManualClone { value: 42 };
    let cloned = m.light_clone();
    assert_eq!(cloned.value, 42);
}

// Test: derived Clone + derived LightClone (the recommended pattern)
#[derive(Clone, LightClone)]
struct DerivedBoth {
    id: u64,
    name: Arc<str>,
}

#[test]
fn test_derived_clone_and_light_clone() {
    let d = DerivedBoth {
        id: 123,
        name: Arc::from("both"),
    };
    let cloned = d.light_clone();
    assert_eq!(cloned.id, 123);
    assert!(Arc::ptr_eq(&d.name, &cloned.name));
}