Add 52893

Issue: rust-lang/rust#52893

ices/52893.rs

@@ -0,0 +1,91 @@
+impl<P, T, Name, F, OLIST: HList, X, Y, FINAL> AddClass<Name, F> for Class<P, T>
+where
+    Self: At<Name>,
+    P: Default,
+    X: Entry,
+    T: Push<(P, F)>,
+    <X as Entry>::Data: Fn(Y) -> Class<P, OLIST>,
+    <Class<P, T> as At<Name>>::AtRes: Push<(P, F)>,
+    <<Class<P, T> as At<Name>>::AtRes as Push<(P, F)>>::PushRes: for<'this> ToRef<'this, Output=HCons<X, Y>> + Push<OLIST>,
+    <<<Class<P, T> as At<Name>>::AtRes as Push<(P, F)>>::PushRes as Push<OLIST>>::PushRes: Entry<Data=FINAL>
+{
+    type Output = Class<P, FINAL>;
+
+    fn init(self, func: F) -> Self::Output {
+        let builder = self.at();
+        let builder = builder.push((P::default(), func));
+        let output = {
+            let refs = builder.to_ref();
+            let func = refs.head.borrow_data();
+            func(refs.tail)
+        };
+        let final_data = builder.push(output);
+        Class {
+            path: P::default(),
+            data: final_data.get_data()
+        }
+    }
+}
+
+struct Class<P, T> {
+    path: P,
+    data: T,
+}
+
+trait At<Name> {
+    type AtRes;
+
+    fn at(self) -> Self::AtRes;
+}
+
+trait Push<T> {
+    type PushRes;
+
+    fn push(self, other: T) -> Self::PushRes;
+}
+
+trait AddClass<Name, F>: At<Name> {
+    type Output;
+
+    fn init(self, func: F) -> Self::Output;
+}
+
+trait Entry {
+    type Data;
+
+    fn get_data(self) -> Self::Data;
+    fn borrow_data(&self) -> &Self::Data;
+}
+
+impl<P: HList, T> Class<P, T> {
+    fn with<Name, F>(self, constructor: F) -> <Self as AddClass<Name, F>>::Output
+    where
+        Self: AddClass<Name, F>,
+    {
+        self.init(constructor)
+    }
+
+    fn from<F>(self, constructor: F) -> <Self as AddClass<P, F>>::Output
+    where
+        Self: AddClass<P, F>,
+    {
+        self.init(constructor)
+    }
+}
+
+fn main() {
+    println!("Hello, world!");
+}
+
+/// Below structs are to bypass the original frunk requirements
+pub trait HList {}
+pub struct HCons<H, T> {
+    pub head: H,
+    pub tail: T,
+}
+
+pub trait ToRef<'a> {
+    type Output;
+
+    fn to_ref(&'a self) -> Self::Output;
+}