1 files changed, 64 insertions, 0 deletions
diff --git a/syn/examples/heapsize/heapsize/src/lib.rs b/syn/examples/heapsize/heapsize/src/lib.rs
new file mode 100644
index 0000000..30bb6d6
--- /dev/null
+++ b/syn/examples/heapsize/heapsize/src/lib.rs
@@ -0,0 +1,64 @@
+use std::mem;
+
+pub use heapsize_derive::*;
+
+pub trait HeapSize {
+    /// Total number of bytes of heap memory owned by `self`.
+    ///
+    /// Does not include the size of `self` itself, which may or may not be on
+    /// the heap. Includes only children of `self`, meaning things pointed to by
+    /// `self`.
+    fn heap_size_of_children(&self) -> usize;
+}
+
+//
+// In a real version of this library there would be lots more impls here, but
+// here are some interesting ones.
+//
+
+impl HeapSize for u8 {
+    /// A `u8` does not own any heap memory.
+    fn heap_size_of_children(&self) -> usize {
+        0
+    }
+}
+
+impl HeapSize for String {
+    /// A `String` owns enough heap memory to hold its reserved capacity.
+    fn heap_size_of_children(&self) -> usize {
+        self.capacity()
+    }
+}
+
+impl<T> HeapSize for Box<T>
+where
+    T: ?Sized + HeapSize,
+{
+    /// A `Box` owns however much heap memory was allocated to hold the value of
+    /// type `T` that we placed on the heap, plus transitively however much `T`
+    /// itself owns.
+    fn heap_size_of_children(&self) -> usize {
+        mem::size_of_val(&**self) + (**self).heap_size_of_children()
+    }
+}
+
+impl<T> HeapSize for [T]
+where
+    T: HeapSize,
+{
+    /// Sum of heap memory owned by each element of a dynamically sized slice of
+    /// `T`.
+    fn heap_size_of_children(&self) -> usize {
+        self.iter().map(HeapSize::heap_size_of_children).sum()
+    }
+}
+
+impl<'a, T> HeapSize for &'a T
+where
+    T: ?Sized,
+{
+    /// A shared reference does not own heap memory.
+    fn heap_size_of_children(&self) -> usize {
+        0
+    }
+}