diff --git a/src/ast.h b/src/ast.h
index 13f0d35..6160efc 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -26,6 +26,7 @@ namespace AST {
         Expression(token::Metadata meta) : Node{ meta } {}
         virtual codegen::StackValue codegen(codegen::Builder& builder, codegen::Scope& scope) = 0;
         virtual std::shared_ptr<types::Type> get_codegen_type(codegen::Scope& scope) = 0;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) = 0;
         virtual std::shared_ptr<types::Type> typecheck(
             typecheck::State& state,
             typecheck::Scope& scope,
@@ -37,6 +38,7 @@ namespace AST {
     public:
         Statement(token::Metadata meta) : Node{ meta } {}
         virtual void codegen(codegen::Builder& builder, codegen::Scope& scope) = 0;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) = 0;
         virtual void typecheck(typecheck::State& state, typecheck::Scope& scope) = 0;
     };
 
@@ -57,6 +59,7 @@ namespace AST {
         virtual std::string formatted() override;
         virtual codegen::StackValue codegen(codegen::Builder& builder, codegen::Scope& scope) override;
         virtual std::shared_ptr<types::Type> get_codegen_type(codegen::Scope& scope) override;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) override;
         virtual std::shared_ptr<types::Type> typecheck(
             typecheck::State& state,
             typecheck::Scope& scope,
@@ -74,6 +77,7 @@ namespace AST {
         virtual std::string formatted() override;
         virtual codegen::StackValue codegen(codegen::Builder& builder, codegen::Scope& scope) override;
         virtual std::shared_ptr<types::Type> get_codegen_type(codegen::Scope& scope) override;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) override;
         virtual std::shared_ptr<types::Type> typecheck(
             typecheck::State& state,
             typecheck::Scope& scope,
@@ -91,6 +95,7 @@ namespace AST {
         virtual std::string formatted() override;
         virtual codegen::StackValue codegen(codegen::Builder& builder, codegen::Scope& scope) override;
         virtual std::shared_ptr<types::Type> get_codegen_type(codegen::Scope& scope) override;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) override;
         virtual std::shared_ptr<types::Type> typecheck(
             typecheck::State& state,
             typecheck::Scope& scope,
@@ -119,6 +124,7 @@ namespace AST {
         virtual std::string formatted() override;
         virtual codegen::StackValue codegen(codegen::Builder& builder, codegen::Scope& scope) override;
         virtual std::shared_ptr<types::Type> get_codegen_type(codegen::Scope& scope) override;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) override;
         virtual std::shared_ptr<types::Type> typecheck(
             typecheck::State& state,
             typecheck::Scope& scope,
@@ -144,6 +150,7 @@ namespace AST {
         virtual std::string formatted() override;
         virtual codegen::StackValue codegen(codegen::Builder& builder, codegen::Scope& scope) override;
         virtual std::shared_ptr<types::Type> get_codegen_type(codegen::Scope& scope) override;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) override;
         virtual std::shared_ptr<types::Type> typecheck(
             typecheck::State& state,
             typecheck::Scope& scope,
@@ -169,6 +176,7 @@ namespace AST {
         virtual std::string formatted() override;
         virtual codegen::StackValue codegen(codegen::Builder& builder, codegen::Scope& scope) override;
         virtual std::shared_ptr<types::Type> get_codegen_type(codegen::Scope& scope) override;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) override;
         virtual std::shared_ptr<types::Type> typecheck(
             typecheck::State& state,
             typecheck::Scope& scope,
@@ -191,6 +199,7 @@ namespace AST {
         virtual std::string formatted() override;
         virtual codegen::StackValue codegen(codegen::Builder& builder, codegen::Scope& scope) override;
         virtual std::shared_ptr<types::Type> get_codegen_type(codegen::Scope& scope) override;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) override;
         virtual std::shared_ptr<types::Type> typecheck(
             typecheck::State& state,
             typecheck::Scope& scope,
@@ -213,6 +222,7 @@ namespace AST {
         virtual std::string formatted() override;
         virtual codegen::StackValue codegen(codegen::Builder& builder, codegen::Scope& scope) override;
         virtual std::shared_ptr<types::Type> get_codegen_type(codegen::Scope& scope) override;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) override;
         virtual std::shared_ptr<types::Type> typecheck(
             typecheck::State& state,
             typecheck::Scope& scope,
@@ -238,6 +248,7 @@ namespace AST {
         virtual std::string formatted() override;
         virtual codegen::StackValue codegen(codegen::Builder& builder, codegen::Scope& scope) override;
         virtual std::shared_ptr<types::Type> get_codegen_type(codegen::Scope& scope) override;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) override;
         virtual std::shared_ptr<types::Type> typecheck(
             typecheck::State& state,
             typecheck::Scope& scope,
@@ -263,6 +274,7 @@ namespace AST {
         virtual std::string formatted() override;
         virtual codegen::StackValue codegen(codegen::Builder& builder, codegen::Scope& scope) override;
         virtual std::shared_ptr<types::Type> get_codegen_type(codegen::Scope& scope) override;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) override;
         virtual std::shared_ptr<types::Type> typecheck(
             typecheck::State& state,
             typecheck::Scope& scope,
@@ -288,6 +300,7 @@ namespace AST {
         virtual std::string formatted() override;
         virtual codegen::StackValue codegen(codegen::Builder& builder, codegen::Scope& scope) override;
         virtual std::shared_ptr<types::Type> get_codegen_type(codegen::Scope& scope) override;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) override;
         virtual std::shared_ptr<types::Type> typecheck(
             typecheck::State& state,
             typecheck::Scope& scope,
@@ -306,6 +319,7 @@ namespace AST {
         virtual ~ReturnStatement() override = default;
         virtual std::string formatted() override;
         virtual void codegen(codegen::Builder& builder, codegen::Scope& scope) override;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) override;
         virtual void typecheck(typecheck::State& state, typecheck::Scope& scope) override;
     };
 
@@ -328,6 +342,7 @@ namespace AST {
         virtual ~InitializationStatement() override = default;
         virtual std::string formatted() override;
         virtual void codegen(codegen::Builder& builder, codegen::Scope& scope) override;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) override;
         virtual void typecheck(typecheck::State& state, typecheck::Scope& scope) override;
     };
 
@@ -341,6 +356,7 @@ namespace AST {
         virtual ~ExpressionStatement() override = default;
         virtual std::string formatted() override;
         virtual void codegen(codegen::Builder& builder, codegen::Scope& scope) override;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) override;
         virtual void typecheck(typecheck::State& state, typecheck::Scope& scope) override;
     };
 
@@ -362,6 +378,7 @@ namespace AST {
         virtual ~IfStatement() override = default;
         virtual std::string formatted() override;
         virtual void codegen(codegen::Builder& builder, codegen::Scope& scope) override;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) override;
         virtual void typecheck(typecheck::State& state, typecheck::Scope& scope) override;
     };
 
@@ -369,6 +386,7 @@ namespace AST {
     public:
         TopLevelStatement(token::Metadata meta) : Node{ meta } {}
         virtual void codegen(codegen::Builder& builder, codegen::Scope& scope) = 0;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) = 0;
         virtual void typecheck(typecheck::State& state, typecheck::Scope& scope) = 0;
     };
 
@@ -397,6 +415,7 @@ namespace AST {
         virtual ~Function() override = default;
         virtual std::string formatted() override;
         virtual void codegen(codegen::Builder& builder, codegen::Scope& scope) override;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) override;
         virtual void typecheck(typecheck::State& state, typecheck::Scope& scope) override;
     };
 
@@ -413,6 +432,7 @@ namespace AST {
         virtual ~TopLevelTypedef() override = default;
         virtual std::string formatted() override;
         virtual void codegen(codegen::Builder& builder, codegen::Scope& scope) override;
+        virtual void typecheck_preprocess(typecheck::Scope& scope) override;
         virtual void typecheck(typecheck::State& state, typecheck::Scope& scope) override;
     };
 }
diff --git a/src/main.cpp b/src/main.cpp
index 490c78a..0b3f096 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -99,16 +99,27 @@ std::optional<CompileOutput> compile(std::string_view in_filename) {
 
     // Perform static analysis
 
+    typecheck::Scope preprocess_scope{};
+
+    // Preprocess
+    for (auto& tls : statements) {
+        std::cout << tls->formatted() << std::endl;
+        tls->typecheck_preprocess(preprocess_scope);
+    }
+
+    // Actual typechecking
     typecheck::State typecheck_state{};
     typecheck_state.binops = types::create_binops();
     typecheck_state.casts = types::create_casts();
 
     typecheck::Scope typecheck_scope{};
+
     for (auto& tls : statements) {
         std::cout << tls->formatted() << std::endl;
         tls->typecheck(typecheck_state, typecheck_scope);
     }
 
+    // Error checking
     if (typecheck_state.errors.size() > 0) {
         std::cerr << "Errors while typechecking:" << std::endl;
         for (auto& error : typecheck_state.errors) {
diff --git a/src/parsing.cpp b/src/parsing.cpp
index c98df24..f27f90a 100644
--- a/src/parsing.cpp
+++ b/src/parsing.cpp
@@ -5,6 +5,8 @@
 
 namespace parsing {
     namespace {
+        static uint32_t struct_id_counter = 0;
+
         Result<std::unique_ptr<AST::Expression>, std::string> parse_expression(token::TokenStream& stream, Scope& scope);
 
         Result<std::shared_ptr<types::Type>, std::string> parse_type(token::TokenStream& stream, Scope& scope) {
@@ -54,12 +56,26 @@ namespace parsing {
                     if (struct_name && !maybe_fields && scope.structs.find(*struct_name) != scope.structs.end()) {
                         auto original_ty = scope.structs[*struct_name];
                         auto original_struct_ty = dynamic_cast<types::StructType*>(original_ty.get());
-                        auto ty = new types::StructType{ struct_name, original_struct_ty->m_fields, true };
+                        auto ty = new types::StructType{ struct_name, original_struct_ty->m_fields, true, false, original_struct_ty->m_id };
                         returned = std::shared_ptr<types::Type>{ ty };
                     }
                     else {
-                        auto ty = new types::StructType{ struct_name, maybe_fields, false };
-                        returned = std::shared_ptr<types::Type>{ ty };
+                        if (scope.structs.find(*struct_name) != scope.structs.end()) {
+                            auto original_ty = scope.structs[*struct_name];
+                            auto original_struct_ty = dynamic_cast<types::StructType*>(original_ty.get());
+                            if (!original_struct_ty->m_fields.has_value()) {
+                                auto ty = new types::StructType{ struct_name, maybe_fields, false, true, original_struct_ty->m_id };
+                                returned = std::shared_ptr<types::Type>{ ty };
+                            }
+                            else {
+                                auto ty = new types::StructType{ struct_name, maybe_fields, false, false, struct_id_counter++ };
+                                returned = std::shared_ptr<types::Type>{ ty };
+                            }
+                        }
+                        else {
+                            auto ty = new types::StructType{ struct_name, maybe_fields, false, false, struct_id_counter++ };
+                            returned = std::shared_ptr<types::Type>{ ty };
+                        }
                     }
                 }
                 else {
@@ -560,7 +576,13 @@ namespace parsing {
             if (ty->m_kind == types::TypeKind::Struct) {
                 auto struct_ty = dynamic_cast<types::StructType*>(ty.get());
                 if (!struct_ty->m_is_ref && struct_ty->m_name) {
-                    scope.structs[*struct_ty->m_name] = ty;
+                    if (scope.structs.find(*struct_ty->m_name) != scope.structs.end() && struct_ty->m_is_def) {
+                        auto true_ty = dynamic_cast<types::StructType*>(scope.structs[*struct_ty->m_name].get());
+                        true_ty->m_fields = struct_ty->m_fields;
+                    }
+                    else {
+                        scope.structs[*struct_ty->m_name] = ty;
+                    }
                 }
             }
 
diff --git a/src/typechecker.cpp b/src/typechecker.cpp
index c0fb498..9c88c5a 100644
--- a/src/typechecker.cpp
+++ b/src/typechecker.cpp
@@ -55,9 +55,56 @@ namespace {
             return expr;
         }
     }
+
+    std::shared_ptr<types::Type> refresh_type(typecheck::Scope& scope, std::shared_ptr<types::Type> ty) {
+        if (ty->m_kind == types::TypeKind::Fundamental) {
+            return ty;
+        }
+        else if (ty->m_kind == types::TypeKind::Array) {
+            auto array_ty = dynamic_cast<types::ArrayType*>(ty.get());
+            array_ty->m_inner = refresh_type(scope, array_ty->m_inner);
+            return ty;
+        }
+        else if (ty->m_kind == types::TypeKind::Function) {
+            auto function_ty = dynamic_cast<types::FunctionType*>(ty.get());
+            function_ty->m_ret_ty = refresh_type(scope, function_ty->m_ret_ty);
+            for (int i = 0; i < static_cast<int>(function_ty->m_param_tys.size()); i++) {
+                function_ty->m_param_tys[i] = refresh_type(scope, function_ty->m_param_tys[i]);
+            }
+            return ty;
+        }
+        else if (ty->m_kind == types::TypeKind::Pointer) {
+            auto ptr_ty = dynamic_cast<types::PointerType*>(ty.get());
+            ptr_ty->m_inner = refresh_type(scope, ptr_ty->m_inner);
+            return ty;
+        }
+        else if (ty->m_kind == types::TypeKind::Struct) {
+            auto struct_ty = dynamic_cast<types::StructType*>(ty.get());
+            if (struct_ty->m_is_ref || struct_ty->m_is_def) {
+                if (scope.structs.find(*struct_ty->m_name) != scope.structs.end()) {
+                    auto pre_existing = dynamic_cast<types::StructType*>(scope.structs[*struct_ty->m_name].get());
+                    struct_ty->m_fields = pre_existing->m_fields;
+                }
+            }
+            if (struct_ty->m_fields) {
+                for (int i = 0; i < static_cast<int>((*struct_ty->m_fields).size()); i++) {
+                    (*struct_ty->m_fields)[i].second = refresh_type(scope, (*struct_ty->m_fields)[i].second);
+                }
+            }
+            return ty;
+        }
+        else {
+            return ty;
+        }
+    }
 }
 
 namespace AST {
+
+    void IntLiteralExpression::typecheck_preprocess(typecheck::Scope& scope) {
+        this->m_ty = refresh_type(scope, this->m_ty);
+    }
+
     std::shared_ptr<types::Type> IntLiteralExpression::typecheck(
         typecheck::State&,
         typecheck::Scope&,
@@ -81,6 +128,8 @@ namespace AST {
         return this->m_ty;
     }
 
+    void StringLiteralExpression::typecheck_preprocess(typecheck::Scope&) {}
+
     std::shared_ptr<types::Type> StringLiteralExpression::typecheck(
         typecheck::State&,
         typecheck::Scope&,
@@ -93,6 +142,8 @@ namespace AST {
         return std::shared_ptr<types::Type>{ptr_ty};
     }
 
+    void ValueReferenceExpression::typecheck_preprocess(typecheck::Scope&) {}
+
     std::shared_ptr<types::Type> ValueReferenceExpression::typecheck(
         typecheck::State& state,
         typecheck::Scope& scope,
@@ -108,6 +159,11 @@ namespace AST {
         };
     }
 
+    void BinaryOperationExpression::typecheck_preprocess(typecheck::Scope& scope) {
+        this->m_lhs->typecheck_preprocess(scope);
+        this->m_rhs->typecheck_preprocess(scope);
+    }
+
     std::shared_ptr<types::Type> BinaryOperationExpression::typecheck(
         typecheck::State& state,
         typecheck::Scope& scope,
@@ -194,6 +250,13 @@ namespace AST {
             new types::FundamentalType{ types::FundamentalTypeKind::Void } };
     }
 
+    void FunctionCallExpression::typecheck_preprocess(typecheck::Scope& scope) {
+        this->m_fn_expr->typecheck_preprocess(scope);
+        for (auto& expr : this->m_args) {
+            expr->typecheck_preprocess(scope);
+        }
+    }
+
     std::shared_ptr<types::Type> FunctionCallExpression::typecheck(
         typecheck::State& state,
         typecheck::Scope& scope,
@@ -234,6 +297,10 @@ namespace AST {
         return fn_ty->m_ret_ty;
     }
 
+    void CastExpression::typecheck_preprocess(typecheck::Scope& scope) {
+        this->m_ty = refresh_type(scope, this->m_ty);
+        this->m_expr->typecheck_preprocess(scope);
+    }
 
     std::shared_ptr<types::Type> CastExpression::typecheck(
         typecheck::State& state,
@@ -253,6 +320,10 @@ namespace AST {
         } };
     }
 
+    void RefExpression::typecheck_preprocess(typecheck::Scope& scope) {
+        this->m_expr->typecheck_preprocess(scope);
+    }
+
     std::shared_ptr<types::Type> RefExpression::typecheck(
         typecheck::State& state,
         typecheck::Scope& scope,
@@ -264,6 +335,10 @@ namespace AST {
         };
     }
 
+    void DerefExpression::typecheck_preprocess(typecheck::Scope& scope) {
+        this->m_expr->typecheck_preprocess(scope);
+    }
+
     std::shared_ptr<types::Type> DerefExpression::typecheck(
         typecheck::State& state,
         typecheck::Scope& scope,
@@ -281,6 +356,10 @@ namespace AST {
         return ptr_ty->m_inner;
     }
 
+    void IndexAccessExpression::typecheck_preprocess(typecheck::Scope& scope) {
+        this->m_expr->typecheck_preprocess(scope);
+    }
+
     std::shared_ptr<types::Type> IndexAccessExpression::typecheck(
         typecheck::State& state,
         typecheck::Scope& scope,
@@ -309,6 +388,10 @@ namespace AST {
         };
     }
 
+    void FieldAccessExpression::typecheck_preprocess(typecheck::Scope& scope) {
+        this->m_expr->typecheck_preprocess(scope);
+    }
+
     std::shared_ptr<types::Type> FieldAccessExpression::typecheck(
         typecheck::State& state,
         typecheck::Scope& scope,
@@ -342,6 +425,13 @@ namespace AST {
         };
     }
 
+    void ListInitializerExpression::typecheck_preprocess(typecheck::Scope& scope) {
+        this->m_ty = refresh_type(scope, this->m_ty);
+        for (auto& expr : this->m_expressions) {
+            expr->typecheck_preprocess(scope);
+        }
+    }
+
     std::shared_ptr<types::Type> ListInitializerExpression::typecheck(
         typecheck::State& state,
         typecheck::Scope& scope,
@@ -435,6 +525,9 @@ namespace AST {
         }
     }
 
+    void ReturnStatement::typecheck_preprocess(typecheck::Scope& scope) {
+        this->m_expr->typecheck_preprocess(scope);
+    }
 
     void ReturnStatement::typecheck(typecheck::State& state, typecheck::Scope& scope) {
         auto res_ty = this->m_expr->typecheck(state, scope, scope.return_ty);
@@ -444,6 +537,12 @@ namespace AST {
         }
     }
 
+    void InitializationStatement::typecheck_preprocess(typecheck::Scope& scope) {
+        this->m_type = refresh_type(scope, this->m_type);
+        if (this->m_expr)
+            (*this->m_expr)->typecheck_preprocess(scope);
+    }
+
     void InitializationStatement::typecheck(typecheck::State& state, typecheck::Scope& scope) {
         if (this->m_expr) {
             auto expr_ty = (*this->m_expr)->typecheck(state, scope, this->m_type);
@@ -453,10 +552,21 @@ namespace AST {
         scope.symbols[this->m_name] = this->m_type;
     }
 
+    void ExpressionStatement::typecheck_preprocess(typecheck::Scope& scope) {
+        this->m_expr->typecheck_preprocess(scope);
+    }
+
     void ExpressionStatement::typecheck(typecheck::State& state, typecheck::Scope& scope) {
         this->m_expr->typecheck(state, scope, {});
     }
 
+    void IfStatement::typecheck_preprocess(typecheck::Scope& scope) {
+        this->m_condition->typecheck_preprocess(scope);
+        this->m_then->typecheck_preprocess(scope);
+        if (this->m_else)
+            (*this->m_else)->typecheck_preprocess(scope);
+    }
+
     void IfStatement::typecheck(typecheck::State& state, typecheck::Scope& scope) {
         auto bool_ty = std::shared_ptr<types::Type>{
             new types::FundamentalType{ types::FundamentalTypeKind::Bool } };
@@ -471,6 +581,19 @@ namespace AST {
         }
     }
 
+    void Function::typecheck_preprocess(typecheck::Scope& scope) {
+        this->m_return_ty = refresh_type(scope, this->m_return_ty);
+        for (auto& param : this->m_params) {
+            param.second = refresh_type(scope, param.second);
+        }
+
+        if (this->m_statements) {
+            for (auto& statement : *this->m_statements) {
+                statement->typecheck_preprocess(scope);
+            }
+        }
+    }
+
     void Function::typecheck(typecheck::State& state, typecheck::Scope& scope) {
         auto return_ty = this->m_return_ty;
         std::vector<std::shared_ptr<types::Type>> param_tys{};
@@ -497,19 +620,26 @@ namespace AST {
         }
     }
 
-    void TopLevelTypedef::typecheck(typecheck::State& state, typecheck::Scope& scope) {
+    void TopLevelTypedef::typecheck_preprocess(typecheck::Scope& scope) {
         if (this->m_ty->m_kind == types::TypeKind::Struct) {
             auto struct_ty = dynamic_cast<types::StructType*>(this->m_ty.get());
-            if (struct_ty->m_is_ref) {
+            if (struct_ty->m_is_ref || struct_ty->m_is_def) {
                 return;
             }
             if (struct_ty->m_name) {
-                if (scope.structs.find(*struct_ty->m_name) == scope.structs.end()) {
-                    scope.structs[*struct_ty->m_name] = this->m_ty;
-                }
-                else {
-                    state.errors.push_back(CompileError("Struct " + *struct_ty->m_name + " declared twice!", this->m_meta));
-                }
+                scope.structs[*struct_ty->m_name] = this->m_ty;
+            }
+        }
+    }
+
+    void TopLevelTypedef::typecheck(typecheck::State&, typecheck::Scope& scope) {
+        if (this->m_ty->m_kind == types::TypeKind::Struct) {
+            auto struct_ty = dynamic_cast<types::StructType*>(this->m_ty.get());
+            if (struct_ty->m_is_ref || struct_ty->m_is_def) {
+                return;
+            }
+            if (struct_ty->m_name) {
+                scope.structs[*struct_ty->m_name] = this->m_ty;
             }
         }
     }
diff --git a/src/types.cpp b/src/types.cpp
index e643b6e..d8b0ffd 100644
--- a/src/types.cpp
+++ b/src/types.cpp
@@ -163,7 +163,7 @@ namespace types {
 
     std::string StructType::formatted() {
         std::stringstream out{ "" };
-        out << "struct";
+        out << "struct(" << this->m_id << ")";
         if (this->m_is_ref)
             out << "(ref)";
         out << " ";
@@ -171,6 +171,7 @@ namespace types {
         if (this->m_name) {
             out << *this->m_name << " ";
         }
+
         if (this->m_fields) {
             out << "{ ";
             int counter = 0;
@@ -262,9 +263,13 @@ namespace types {
             auto ty1 = dynamic_cast<StructType*>(type1.get());
             auto ty2 = dynamic_cast<StructType*>(type2.get());
 
+            if (ty1->m_is_ref || ty2->m_is_ref)
+                return ty1->m_id == ty2->m_id;
+
             if (ty1->m_fields.has_value() != ty2->m_fields.has_value())
                 return false;
 
+
             if (ty1->m_fields) {
                 if (ty1->m_fields->size() != ty2->m_fields->size())
                     return false;
diff --git a/src/types.h b/src/types.h
index e9f923a..c649cd4 100644
--- a/src/types.h
+++ b/src/types.h
@@ -105,9 +105,11 @@ namespace types {
         std::optional<std::string> m_name;
         std::optional<std::vector<StructField>> m_fields;
         bool m_is_ref;
+        bool m_is_def;
+        uint32_t m_id;
 
-        StructType(std::optional<std::string> name, std::optional<std::vector<StructField>> fields, bool is_ref)
-            : Type(TypeKind::Struct), m_name{ name }, m_fields{ fields }, m_is_ref{ is_ref } {
+        StructType(std::optional<std::string> name, std::optional<std::vector<StructField>> fields, bool is_ref, bool is_def, uint32_t id)
+            : Type(TypeKind::Struct), m_name{ name }, m_fields{ fields }, m_is_ref{ is_ref }, m_is_def{ is_def }, m_id{ id } {
         }
         virtual ~StructType() override = default;
         virtual std::string formatted() override;
diff --git a/test.c b/test.c
index 04f99bc..59f59f1 100644
--- a/test.c
+++ b/test.c
@@ -10,8 +10,14 @@ void change_first(char otus[5]) {
     otus[0] = 115;
 }
 
+
+struct Otus;
+
+void update(struct Otus potus) {
+    potus.field = 20;
+}
 struct Otus {
-    int field
+    int field;
 };
 
 int main() {
@@ -25,6 +31,7 @@ int main() {
     printf(" first element: %d!", somelist[0]);
 
     struct Otus otus = { 5 };
+    update(otus);
 
     printf(" first field: %d!", otus.field);