diff --git a/mlir/include/mlir/IR/OpBase.td b/mlir/include/mlir/IR/OpBase.td
--- a/mlir/include/mlir/IR/OpBase.td
+++ b/mlir/include/mlir/IR/OpBase.td
@@ -1681,7 +1681,16 @@
 //===----------------------------------------------------------------------===//
 
 // Trait represents a trait regarding an attribute, operation, or type.
-class Trait;
+class Trait {
+  // Additional code that will be added to the public part of the generated
+  // C++ code of the entity (attribute, operation, or type) declaration.
+  code extraInjectedClassDeclaration = "";
+
+  // Additional code that will be added to the generated source file. The
+  // generated code is placed inside the entity's C++ namespace. `$cppClass` is
+  // replaced by the entity's C++ class name.
+  code extraInjectedClassDefinition = "";
+}
 
 // Define a Trait corresponding to a list of Traits, this allows for specifying
 // a list of traits as trait. Avoids needing to do `[Traits, ...] # ListOfTraits
diff --git a/mlir/include/mlir/TableGen/Operator.h b/mlir/include/mlir/TableGen/Operator.h
--- a/mlir/include/mlir/TableGen/Operator.h
+++ b/mlir/include/mlir/TableGen/Operator.h
@@ -235,10 +235,10 @@
   StringRef getAssemblyFormat() const;
 
   // Returns this op's extra class declaration code.
-  StringRef getExtraClassDeclaration() const;
+  std::string getExtraClassDeclaration() const;
 
   // Returns this op's extra class definition code.
-  StringRef getExtraClassDefinition() const;
+  std::string getExtraClassDefinition() const;
 
   // Returns the Tablegen definition this operator was constructed from.
   // TODO: do not expose the TableGen record, this is a temporary solution to
diff --git a/mlir/include/mlir/TableGen/Trait.h b/mlir/include/mlir/TableGen/Trait.h
--- a/mlir/include/mlir/TableGen/Trait.h
+++ b/mlir/include/mlir/TableGen/Trait.h
@@ -53,6 +53,9 @@
   // Returns the Tablegen definition this operator was constructed from.
   const llvm::Record &getDef() const { return *def; }
 
+  StringRef getExtraInjectedClassDeclaration() const;
+  StringRef getExtraInjectedClassDefinition() const;
+
 protected:
   // The TableGen definition of this trait.
   const llvm::Record *def;
diff --git a/mlir/lib/TableGen/Operator.cpp b/mlir/lib/TableGen/Operator.cpp
--- a/mlir/lib/TableGen/Operator.cpp
+++ b/mlir/lib/TableGen/Operator.cpp
@@ -121,18 +121,34 @@
   return results->getNumArgs();
 }
 
-StringRef Operator::getExtraClassDeclaration() const {
+std::string Operator::getExtraClassDeclaration() const {
   constexpr auto attr = "extraClassDeclaration";
-  if (def.isValueUnset(attr))
-    return {};
-  return def.getValueAsString(attr);
+  std::string value;
+  if (!def.isValueUnset(attr))
+    value = def.getValueAsString(attr).str();
+  for (auto &trait : getTraits()) {
+    StringRef traitDeclaration = trait.getExtraInjectedClassDeclaration();
+    if (!traitDeclaration.empty()) {
+      value += "\n";
+      value += traitDeclaration.str();
+    }
+  }
+  return value;
 }
 
-StringRef Operator::getExtraClassDefinition() const {
+std::string Operator::getExtraClassDefinition() const {
   constexpr auto attr = "extraClassDefinition";
-  if (def.isValueUnset(attr))
-    return {};
-  return def.getValueAsString(attr);
+  std::string value;
+  if (!def.isValueUnset(attr))
+    value = def.getValueAsString(attr).str();
+  for (auto &trait : getTraits()) {
+    StringRef traitDefinition = trait.getExtraInjectedClassDefinition();
+    if (!traitDefinition.empty()) {
+      value += "\n";
+      value += traitDefinition.str();
+    }
+  }
+  return value;
 }
 
 const llvm::Record &Operator::getDef() const { return def; }
diff --git a/mlir/lib/TableGen/Trait.cpp b/mlir/lib/TableGen/Trait.cpp
--- a/mlir/lib/TableGen/Trait.cpp
+++ b/mlir/lib/TableGen/Trait.cpp
@@ -39,6 +39,20 @@
 
 Trait::Trait(Kind kind, const llvm::Record *def) : def(def), kind(kind) {}
 
+StringRef Trait::getExtraInjectedClassDeclaration() const {
+  constexpr auto attr = "extraInjectedClassDeclaration";
+  if (def->isValueUnset(attr))
+    return {};
+  return def->getValueAsString(attr);
+}
+
+StringRef Trait::getExtraInjectedClassDefinition() const {
+  constexpr auto attr = "extraInjectedClassDefinition";
+  if (def->isValueUnset(attr))
+    return {};
+  return def->getValueAsString(attr);
+}
+
 //===----------------------------------------------------------------------===//
 // NativeTrait
 //===----------------------------------------------------------------------===//
diff --git a/mlir/test/lib/Dialect/Test/TestOps.td b/mlir/test/lib/Dialect/Test/TestOps.td
--- a/mlir/test/lib/Dialect/Test/TestOps.td
+++ b/mlir/test/lib/Dialect/Test/TestOps.td
@@ -479,6 +479,24 @@
 // Test Traits
 //===----------------------------------------------------------------------===//
 
+def OpTraitWithInjectedCode : NativeOpTrait<"SameOperandsElementType"> {
+  code extraInjectedClassDeclaration = [{
+    bool testInjection();
+  }];
+  code extraInjectedClassDefinition = [{
+    bool $cppClass::testInjection() {
+      return true;
+    }
+  }];
+}
+
+def SameOperandElementTypeInjectedOp : TEST_Op<"same_operand_element_type_injected_code",
+    [OpTraitWithInjectedCode]> {
+  let arguments = (ins AnyType, AnyType);
+  let results = (outs AnyType);
+}
+
+
 def SameOperandElementTypeOp : TEST_Op<"same_operand_element_type",
     [SameOperandsElementType]> {
   let arguments = (ins AnyType, AnyType);
diff --git a/mlir/tools/mlir-tblgen/OpClass.h b/mlir/tools/mlir-tblgen/OpClass.h
--- a/mlir/tools/mlir-tblgen/OpClass.h
+++ b/mlir/tools/mlir-tblgen/OpClass.h
@@ -25,7 +25,7 @@
   /// - inheritance of `print`
   /// - a type alias for the associated adaptor class
   ///
-  OpClass(StringRef name, StringRef extraClassDeclaration,
+  OpClass(StringRef name, std::string extraClassDeclaration,
           std::string extraClassDefinition);
 
   /// Add an op trait.
@@ -39,7 +39,7 @@
 
 private:
   /// Hand-written extra class declarations.
-  StringRef extraClassDeclaration;
+  std::string extraClassDeclaration;
   /// Hand-written extra class definitions.
   std::string extraClassDefinition;
   /// The parent class, which also contains the traits to be inherited.
diff --git a/mlir/tools/mlir-tblgen/OpClass.cpp b/mlir/tools/mlir-tblgen/OpClass.cpp
--- a/mlir/tools/mlir-tblgen/OpClass.cpp
+++ b/mlir/tools/mlir-tblgen/OpClass.cpp
@@ -15,9 +15,10 @@
 // OpClass definitions
 //===----------------------------------------------------------------------===//
 
-OpClass::OpClass(StringRef name, StringRef extraClassDeclaration,
+OpClass::OpClass(StringRef name, std::string extraClassDeclaration,
                  std::string extraClassDefinition)
-    : Class(name.str()), extraClassDeclaration(extraClassDeclaration),
+    : Class(name.str()),
+      extraClassDeclaration(std::move(extraClassDeclaration)),
       extraClassDefinition(std::move(extraClassDefinition)),
       parent(addParent("::mlir::Op")) {
   parent.addTemplateParam(getClassName().str());