add alices quiz (no explanation) as quiz misc 8

Author: jdonszelmann

code/examples/misc_8.rs

@@ -0,0 +1,39 @@
+use core::pin::Pin;
+use core::marker::PhantomPinned;
+
+#[derive(Default)]
+struct MyPinnedType {
+    addr: usize,
+    _pin: PhantomPinned,
+}
+
+impl MyPinnedType {
+    fn my_pin_fn(self: Pin<&mut Self>) {
+        let me = unsafe { Pin::into_inner_unchecked(self) };
+        let me_addr = me as *mut Self as usize;
+        if me.addr == 0 {
+            me.addr = me_addr;
+        } else {
+            assert_eq!(me.addr, me_addr, "Pinned value was moved.")
+        }
+    }
+}
+
+trait MyUnpinTrait {
+    fn into_pinned_type(self: Pin<&mut Self>) -> Pin<&mut MyPinnedType>;
+}
+impl MyUnpinTrait for MyPinnedType {
+    fn into_pinned_type(self: Pin<&mut Self>) -> Pin<&mut MyPinnedType> {
+        self
+    }
+}
+impl Unpin for dyn MyUnpinTrait {}
+
+fn main() {
+    let mut pinned_type = MyPinnedType::default();
+    
+    Pin::new((&mut pinned_type) as &mut dyn MyUnpinTrait).into_pinned_type().my_pin_fn();
+    
+    let pinned_type = Box::new(pinned_type);
+    Pin::from(pinned_type).as_mut().my_pin_fn();
+}

code/examples/stderr/misc_8.stderr

@@ -0,0 +1,8 @@
+error[E0321]: cross-crate traits with a default impl, like `Unpin`, can only be implemented for a struct/enum type, not `(dyn MyUnpinTrait + 'static)`
+  --> examples/misc_8.rs:30:1
+   |
+30 | impl Unpin for dyn MyUnpinTrait {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ can't implement cross-crate trait with a default impl for non-struct/enum type
+
+For more information about this error, try `rustc --explain E0321`.
+error: could not compile `code` (example "misc_8") due to 1 previous error

src/SUMMARY.md

@@ -11,6 +11,7 @@
 # Miscellaneous
 
 - [Miscellaneous 1](./misc/1.md)
+- [Miscellaneous 8](./misc/8.md)
 
 # Trait Solver
 

src/misc/8.md

@@ -0,0 +1,14 @@
+# Misc 8 @Darksonn
+
+```rust
+{{#include ../../code/examples/misc_8.rs}}
+```
+
+<details>
+<summary>Solution</summary>
+
+```
+{{#include ../../code/examples/stderr/misc_8.stderr}}
+```
+
+</details>