1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38

use crate::cc::GcHeader;
use std::any::Any;

/// Callback function that serves as the parameter of
/// [`Trace::trace`](trait.Trace.html#method.trace).
pub type Tracer<'a> = dyn FnMut(&mut GcHeader) + 'a;

/// Defines how the cycle collector should collect a type.
pub trait Trace: 'static {
    /// Traverse through values referred by this value.
    ///
    /// For example, if `self.x` is a value referred by `self`,
    /// call `self.x.trace(tracer)`.
    ///
    /// Do not call the `trace` function directly.
    fn trace(&self, tracer: &mut Tracer) {
        let _ = tracer;
    }

    /// Whether this type should be tracked by the cycle collector.
    /// This provides an optimization that makes atomic types opt
    /// out the cycle collector.
    ///
    /// This is ideally an associated constant. However that is
    /// currently impossible due to compiler limitations.
    /// See https://doc.rust-lang.org/error-index.html#E0038.
    fn is_type_tracked(&self) -> bool {
        true
    }

    /// Provide downcast support.
    ///
    /// Types that wants downcast support should implement this method like:
    /// `fn as_any(&self) -> Option<&dyn std::any::Any> { Some(self) }`
    fn as_any(&self) -> Option<&dyn Any> {
        None
    }
}