[mlir:toy][NFC] Remove unnecessary trailing return type

In this instance, the trailing return type does not improve readability
as it repeats what is returned in the same line.

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D125697

mlir/examples/toy/Ch1/include/toy/AST.h

@@ -234,8 +234,8 @@ public:
   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 &);

mlir/examples/toy/Ch2/include/toy/AST.h

@@ -234,8 +234,8 @@ public:
   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 &);

mlir/examples/toy/Ch3/include/toy/AST.h

@@ -234,8 +234,8 @@ public:
   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 &);

mlir/examples/toy/Ch4/include/toy/AST.h

@@ -234,8 +234,8 @@ public:
   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 &);

mlir/examples/toy/Ch5/include/toy/AST.h

@@ -234,8 +234,8 @@ public:
   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 &);

mlir/examples/toy/Ch6/include/toy/AST.h

@@ -234,8 +234,8 @@ public:
   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 &);

mlir/examples/toy/Ch7/include/toy/AST.h

@@ -301,8 +301,8 @@ public:
   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 &);