diff --git a/mlir/examples/toy/Ch1/include/toy/AST.h b/mlir/examples/toy/Ch1/include/toy/AST.h
--- a/mlir/examples/toy/Ch1/include/toy/AST.h
+++ b/mlir/examples/toy/Ch1/include/toy/AST.h
@@ -234,8 +234,8 @@
   ModuleAST(std::vector<FunctionAST> functions)
       : functions(std::move(functions)) {}
 
-  auto begin() -> decltype(functions.begin()) { return functions.begin(); }
-  auto end() -> decltype(functions.end()) { return functions.end(); }
+  auto begin() { return functions.begin(); }
+  auto end() { return functions.end(); }
 };
 
 void dump(ModuleAST &);
diff --git a/mlir/examples/toy/Ch2/include/toy/AST.h b/mlir/examples/toy/Ch2/include/toy/AST.h
--- a/mlir/examples/toy/Ch2/include/toy/AST.h
+++ b/mlir/examples/toy/Ch2/include/toy/AST.h
@@ -234,8 +234,8 @@
   ModuleAST(std::vector<FunctionAST> functions)
       : functions(std::move(functions)) {}
 
-  auto begin() -> decltype(functions.begin()) { return functions.begin(); }
-  auto end() -> decltype(functions.end()) { return functions.end(); }
+  auto begin() { return functions.begin(); }
+  auto end() { return functions.end(); }
 };
 
 void dump(ModuleAST &);
diff --git a/mlir/examples/toy/Ch3/include/toy/AST.h b/mlir/examples/toy/Ch3/include/toy/AST.h
--- a/mlir/examples/toy/Ch3/include/toy/AST.h
+++ b/mlir/examples/toy/Ch3/include/toy/AST.h
@@ -234,8 +234,8 @@
   ModuleAST(std::vector<FunctionAST> functions)
       : functions(std::move(functions)) {}
 
-  auto begin() -> decltype(functions.begin()) { return functions.begin(); }
-  auto end() -> decltype(functions.end()) { return functions.end(); }
+  auto begin() { return functions.begin(); }
+  auto end() { return functions.end(); }
 };
 
 void dump(ModuleAST &);
diff --git a/mlir/examples/toy/Ch4/include/toy/AST.h b/mlir/examples/toy/Ch4/include/toy/AST.h
--- a/mlir/examples/toy/Ch4/include/toy/AST.h
+++ b/mlir/examples/toy/Ch4/include/toy/AST.h
@@ -234,8 +234,8 @@
   ModuleAST(std::vector<FunctionAST> functions)
       : functions(std::move(functions)) {}
 
-  auto begin() -> decltype(functions.begin()) { return functions.begin(); }
-  auto end() -> decltype(functions.end()) { return functions.end(); }
+  auto begin() { return functions.begin(); }
+  auto end() { return functions.end(); }
 };
 
 void dump(ModuleAST &);
diff --git a/mlir/examples/toy/Ch5/include/toy/AST.h b/mlir/examples/toy/Ch5/include/toy/AST.h
--- a/mlir/examples/toy/Ch5/include/toy/AST.h
+++ b/mlir/examples/toy/Ch5/include/toy/AST.h
@@ -234,8 +234,8 @@
   ModuleAST(std::vector<FunctionAST> functions)
       : functions(std::move(functions)) {}
 
-  auto begin() -> decltype(functions.begin()) { return functions.begin(); }
-  auto end() -> decltype(functions.end()) { return functions.end(); }
+  auto begin() { return functions.begin(); }
+  auto end() { return functions.end(); }
 };
 
 void dump(ModuleAST &);
diff --git a/mlir/examples/toy/Ch6/include/toy/AST.h b/mlir/examples/toy/Ch6/include/toy/AST.h
--- a/mlir/examples/toy/Ch6/include/toy/AST.h
+++ b/mlir/examples/toy/Ch6/include/toy/AST.h
@@ -234,8 +234,8 @@
   ModuleAST(std::vector<FunctionAST> functions)
       : functions(std::move(functions)) {}
 
-  auto begin() -> decltype(functions.begin()) { return functions.begin(); }
-  auto end() -> decltype(functions.end()) { return functions.end(); }
+  auto begin() { return functions.begin(); }
+  auto end() { return functions.end(); }
 };
 
 void dump(ModuleAST &);
diff --git a/mlir/examples/toy/Ch7/include/toy/AST.h b/mlir/examples/toy/Ch7/include/toy/AST.h
--- a/mlir/examples/toy/Ch7/include/toy/AST.h
+++ b/mlir/examples/toy/Ch7/include/toy/AST.h
@@ -301,8 +301,8 @@
   ModuleAST(std::vector<std::unique_ptr<RecordAST>> records)
       : records(std::move(records)) {}
 
-  auto begin() -> decltype(records.begin()) { return records.begin(); }
-  auto end() -> decltype(records.end()) { return records.end(); }
+  auto begin() { return records.begin(); }
+  auto end() { return records.end(); }
 };
 
 void dump(ModuleAST &);