From 088f4c502f9fcba5f39d255ff6cdcf2ab050b201 Mon Sep 17 00:00:00 2001
From: Alex Zinenko <zinenko@google.com>
Date: Wed, 2 Oct 2019 09:15:53 -0700
Subject: [PATCH] Fix example in OpInterfaces documentation

The concept-based polymorphism structure was missing an inheritance link
between the concept and the model. The interface class did not re-export the
base class constructor, which made it unusable with llvm::isa calls. Fix these
and reformat the code around.

PiperOrigin-RevId: 272452062
---
 mlir/g3doc/Interfaces.md | 35 +++++++++++++++++++----------------
 1 file changed, 19 insertions(+), 16 deletions(-)

diff --git a/mlir/g3doc/Interfaces.md b/mlir/g3doc/Interfaces.md
index 004a65c..c4d517b 100644
--- a/mlir/g3doc/Interfaces.md
+++ b/mlir/g3doc/Interfaces.md
@@ -124,26 +124,29 @@ registration.
 
 ```c++
 struct ExampleOpInterfaceTraits {
-/// Define a base concept class that defines the virtual interface that needs
-/// to be overridden.
-struct Concept {
-  virtual ~Concept();
-  virtual unsigned getNumInputs(Operation *op) = 0;
-};
-
-/// Define a model class that specializes a concept on a given operation type.
-template <typename OpT>
-struct Model {
-  /// Override the method to dispatch on the concrete operation.
-  unsigned getNumInputs(Operation *op) final {
-    return llvm::cast<OpT>(op).getNumInputs();
-  }
-};
+  /// Define a base concept class that defines the virtual interface that needs
+  /// to be overridden.
+  struct Concept {
+    virtual ~Concept();
+    virtual unsigned getNumInputs(Operation *op) = 0;
+  };
+
+  /// Define a model class that specializes a concept on a given operation type.
+  template <typename OpT>
+  struct Model : public Concept {
+    /// Override the method to dispatch on the concrete operation.
+    unsigned getNumInputs(Operation *op) final {
+      return llvm::cast<OpT>(op).getNumInputs();
+    }
+  };
 };
 
 class ExampleOpInterface : public OpInterface<ExampleOpInterface,
                                               ExampleOpInterfaceTraits> {
 public:
+  /// Use base class constructor to support LLVM-style casts.
+  using OpInterface<ExampleOpInterface, ExampleOpInterfaceTraits>::OpInterface;
+
   /// The interface dispatches to 'getImpl()', an instance of the concept.
   unsigned getNumInputs() {
     return getImpl()->getNumInputs(getOperation());
@@ -169,7 +172,7 @@ public:
 /// interface.
 Operation *op = ...;
 if (ExampleOpInterface example = dyn_cast<ExampleOpInterface>(op))
- llvm::errs() << "num inputs = " << example.getNumInputs() << "\n";
+  llvm::errs() << "num inputs = " << example.getNumInputs() << "\n";
 ```
 
 #### Utilizing the ODS Framework
-- 
2.7.4