introduce Subtype type_op

src/librustc_mir/borrow_check/nll/type_check/mod.rs

@@ -826,11 +826,7 @@ fn sub_types(
         self.fully_perform_op(
             locations,
             || format!("sub_types({:?} <: {:?})", sub, sup),
-            CustomTypeOp::new(|this| {
-                this.infcx
-                    .at(&ObligationCause::dummy(), this.param_env)
-                    .sup(sup, sub)
-            }),
+            type_op::Subtype::new(sub, sup),
         )
     }
 

src/librustc_mir/borrow_check/nll/type_check/type_op.rs

@@ -10,19 +10,23 @@
 
 use borrow_check::nll::type_check::TypeChecker;
 use rustc::infer::InferResult;
+use rustc::traits::ObligationCause;
+use rustc::ty::Ty;
 
 pub(super) trait TypeOp<'gcx, 'tcx> {
     type Output;
 
-    fn perform(self, type_checker: &mut TypeChecker<'_, 'gcx, 'tcx>) -> InferResult<'tcx, Self::Output>;
+    fn perform(
+        self,
+        type_checker: &mut TypeChecker<'_, 'gcx, 'tcx>,
+    ) -> InferResult<'tcx, Self::Output>;
 }
 
 pub(super) struct CustomTypeOp<F> {
-    closure: F
+    closure: F,
 }
 
-impl<F> CustomTypeOp<F>
-{
+impl<F> CustomTypeOp<F> {
     pub(super) fn new<'gcx, 'tcx, R>(closure: F) -> Self
     where
         F: FnOnce(&mut TypeChecker<'_, 'gcx, 'tcx>) -> InferResult<'tcx, R>,
@@ -41,3 +45,25 @@ fn perform(self, type_checker: &mut TypeChecker<'_, 'gcx, 'tcx>) -> InferResult<
         (self.closure)(type_checker)
     }
 }
+
+pub(super) struct Subtype<'tcx> {
+    sub: Ty<'tcx>,
+    sup: Ty<'tcx>,
+}
+
+impl<'tcx> Subtype<'tcx> {
+    pub(super) fn new(sub: Ty<'tcx>, sup: Ty<'tcx>) -> Self {
+        Self { sub, sup }
+    }
+}
+
+impl<'gcx, 'tcx> TypeOp<'gcx, 'tcx> for Subtype<'tcx> {
+    type Output = ();
+
+    fn perform(self, type_checker: &mut TypeChecker<'_, 'gcx, 'tcx>) -> InferResult<'tcx, Self::Output> {
+        type_checker.infcx
+            .at(&ObligationCause::dummy(), type_checker.param_env)
+            .sup(self.sup, self.sub)
+    }
+}
+