diff --git a/src/ast/access_decoration.h b/src/ast/access_decoration.h
index dcf2d950e2..e58c13a228 100644
--- a/src/ast/access_decoration.h
+++ b/src/ast/access_decoration.h
@@ -49,7 +49,7 @@ class AccessDecoration : public Castable<AccessDecoration, TypeDecoration> {
   AccessDecoration* Clone(CloneContext* ctx) const override;
 
  private:
-  AccessControl value_ = ast::AccessControl::kReadWrite;
+  AccessControl const value_;
 };
 
 }  // namespace ast
diff --git a/src/ast/array_accessor_expression.h b/src/ast/array_accessor_expression.h
index d35c20a172..ebcf9c63c0 100644
--- a/src/ast/array_accessor_expression.h
+++ b/src/ast/array_accessor_expression.h
@@ -64,8 +64,8 @@ class ArrayAccessorExpression
  private:
   ArrayAccessorExpression(const ArrayAccessorExpression&) = delete;
 
-  Expression* array_ = nullptr;
-  Expression* idx_expr_ = nullptr;
+  Expression* const array_;
+  Expression* const idx_expr_;
 };
 
 }  // namespace ast
diff --git a/src/ast/assignment_statement.h b/src/ast/assignment_statement.h
index a91b0000ae..01b5ac5265 100644
--- a/src/ast/assignment_statement.h
+++ b/src/ast/assignment_statement.h
@@ -61,8 +61,8 @@ class AssignmentStatement : public Castable<AssignmentStatement, Statement> {
  private:
   AssignmentStatement(const AssignmentStatement&) = delete;
 
-  Expression* lhs_ = nullptr;
-  Expression* rhs_ = nullptr;
+  Expression* const lhs_;
+  Expression* const rhs_;
 };
 
 }  // namespace ast
diff --git a/src/ast/binary_expression.h b/src/ast/binary_expression.h
index 8283a5dbda..9bce5489e5 100644
--- a/src/ast/binary_expression.h
+++ b/src/ast/binary_expression.h
@@ -127,9 +127,9 @@ class BinaryExpression : public Castable<BinaryExpression, Expression> {
  private:
   BinaryExpression(const BinaryExpression&) = delete;
 
-  BinaryOp op_ = BinaryOp::kNone;
-  Expression* lhs_ = nullptr;
-  Expression* rhs_ = nullptr;
+  BinaryOp const op_;
+  Expression* const lhs_;
+  Expression* const rhs_;
 };
 
 inline std::ostream& operator<<(std::ostream& out, BinaryOp op) {
diff --git a/src/ast/binding_decoration.h b/src/ast/binding_decoration.h
index ae4cc4504a..e4d73e3698 100644
--- a/src/ast/binding_decoration.h
+++ b/src/ast/binding_decoration.h
@@ -49,7 +49,7 @@ class BindingDecoration
   BindingDecoration* Clone(CloneContext* ctx) const override;
 
  private:
-  uint32_t value_;
+  uint32_t const value_;
 };
 
 }  // namespace ast
diff --git a/src/ast/bitcast_expression.h b/src/ast/bitcast_expression.h
index 5ef92b3fc3..ccee67edf2 100644
--- a/src/ast/bitcast_expression.h
+++ b/src/ast/bitcast_expression.h
@@ -61,8 +61,8 @@ class BitcastExpression : public Castable<BitcastExpression, Expression> {
  private:
   BitcastExpression(const BitcastExpression&) = delete;
 
-  type::Type* type_ = nullptr;
-  Expression* expr_ = nullptr;
+  type::Type* const type_;
+  Expression* const expr_;
 };
 
 }  // namespace ast
diff --git a/src/ast/block_statement.h b/src/ast/block_statement.h
index d485bdf7a6..08e4b066bf 100644
--- a/src/ast/block_statement.h
+++ b/src/ast/block_statement.h
@@ -83,7 +83,7 @@ class BlockStatement : public Castable<BlockStatement, Statement> {
  private:
   BlockStatement(const BlockStatement&) = delete;
 
-  StatementList statements_;
+  StatementList const statements_;
 };
 
 }  // namespace ast
diff --git a/src/ast/bool_literal.h b/src/ast/bool_literal.h
index 1b984f5f2d..2896913d33 100644
--- a/src/ast/bool_literal.h
+++ b/src/ast/bool_literal.h
@@ -52,7 +52,7 @@ class BoolLiteral : public Castable<BoolLiteral, Literal> {
   BoolLiteral* Clone(CloneContext* ctx) const override;
 
  private:
-  bool value_;
+  bool const value_;
 };
 
 }  // namespace ast
diff --git a/src/ast/builtin_decoration.h b/src/ast/builtin_decoration.h
index 5a1419bee3..7c437d50e4 100644
--- a/src/ast/builtin_decoration.h
+++ b/src/ast/builtin_decoration.h
@@ -48,7 +48,7 @@ class BuiltinDecoration
   BuiltinDecoration* Clone(CloneContext* ctx) const override;
 
  private:
-  Builtin builtin_ = Builtin::kNone;
+  Builtin const builtin_;
 };
 
 }  // namespace ast
diff --git a/src/ast/call_expression.h b/src/ast/call_expression.h
index c5547e90d9..d52ab4e5d7 100644
--- a/src/ast/call_expression.h
+++ b/src/ast/call_expression.h
@@ -60,8 +60,8 @@ class CallExpression : public Castable<CallExpression, Expression> {
  private:
   CallExpression(const CallExpression&) = delete;
 
-  Expression* func_ = nullptr;
-  ExpressionList params_;
+  Expression* const func_;
+  ExpressionList const params_;
 };
 
 }  // namespace ast
diff --git a/src/ast/call_statement.h b/src/ast/call_statement.h
index 59f7bed14b..c8aa837010 100644
--- a/src/ast/call_statement.h
+++ b/src/ast/call_statement.h
@@ -57,7 +57,7 @@ class CallStatement : public Castable<CallStatement, Statement> {
  private:
   CallStatement(const CallStatement&) = delete;
 
-  CallExpression* call_ = nullptr;
+  CallExpression* const call_;
 };
 
 }  // namespace ast
diff --git a/src/ast/case_statement.h b/src/ast/case_statement.h
index c9c424e8b8..b7933422cb 100644
--- a/src/ast/case_statement.h
+++ b/src/ast/case_statement.h
@@ -73,8 +73,8 @@ class CaseStatement : public Castable<CaseStatement, Statement> {
  private:
   CaseStatement(const CaseStatement&) = delete;
 
-  CaseSelectorList selectors_;
-  BlockStatement* body_ = nullptr;
+  CaseSelectorList const selectors_;
+  BlockStatement* const body_;
 };
 
 /// A list of case statements
diff --git a/src/ast/constant_id_decoration.h b/src/ast/constant_id_decoration.h
index bb990ae254..0d2b407769 100644
--- a/src/ast/constant_id_decoration.h
+++ b/src/ast/constant_id_decoration.h
@@ -48,7 +48,7 @@ class ConstantIdDecoration
   ConstantIdDecoration* Clone(CloneContext* ctx) const override;
 
  private:
-  uint32_t value_ = 0;
+  uint32_t const value_;
 };
 
 }  // namespace ast
diff --git a/src/ast/else_statement.h b/src/ast/else_statement.h
index 646672028d..7b08fa53ed 100644
--- a/src/ast/else_statement.h
+++ b/src/ast/else_statement.h
@@ -69,8 +69,8 @@ class ElseStatement : public Castable<ElseStatement, Statement> {
  private:
   ElseStatement(const ElseStatement&) = delete;
 
-  Expression* condition_ = nullptr;
-  BlockStatement* body_ = nullptr;
+  Expression* const condition_;
+  BlockStatement* const body_;
 };
 
 /// A list of else statements
diff --git a/src/ast/expression.h b/src/ast/expression.h
index 5809d2e912..12e038cfa5 100644
--- a/src/ast/expression.h
+++ b/src/ast/expression.h
@@ -52,7 +52,7 @@ class Expression : public Castable<Expression, Node> {
  private:
   Expression(const Expression&) = delete;
 
-  type::Type* result_type_ = nullptr;
+  type::Type* result_type_ = nullptr;  // Semantic info
 };
 
 /// A list of expressions
diff --git a/src/ast/float_literal.h b/src/ast/float_literal.h
index ad33124932..bbf58f838d 100644
--- a/src/ast/float_literal.h
+++ b/src/ast/float_literal.h
@@ -50,7 +50,7 @@ class FloatLiteral : public Castable<FloatLiteral, Literal> {
   FloatLiteral* Clone(CloneContext* ctx) const override;
 
  private:
-  float value_;
+  float const value_;
 };
 
 }  // namespace ast
diff --git a/src/ast/function.h b/src/ast/function.h
index 14b6789376..4f22016b2a 100644
--- a/src/ast/function.h
+++ b/src/ast/function.h
@@ -202,15 +202,16 @@ class Function : public Castable<Function, Node> {
   const std::vector<std::pair<Variable*, Function::BindingInfo>>
   ReferencedSampledTextureVariablesImpl(bool multisampled) const;
 
-  Symbol symbol_;
-  std::string name_;
-  VariableList params_;
-  type::Type* return_type_ = nullptr;
-  BlockStatement* body_ = nullptr;
-  std::vector<Variable*> referenced_module_vars_;
-  std::vector<Variable*> local_referenced_module_vars_;
-  std::vector<Symbol> ancestor_entry_points_;
-  FunctionDecorationList decorations_;
+  Symbol const symbol_;
+  std::string const name_;
+  VariableList const params_;
+  type::Type* const return_type_;
+  BlockStatement* const body_;
+
+  std::vector<Variable*> referenced_module_vars_;        // Semantic info
+  std::vector<Variable*> local_referenced_module_vars_;  // Semantic info
+  std::vector<Symbol> ancestor_entry_points_;            // Semantic info
+  FunctionDecorationList decorations_;                   // Semantic info
 };
 
 /// A list of functions
diff --git a/src/ast/identifier_expression.h b/src/ast/identifier_expression.h
index 40750daaad..b30c4cc282 100644
--- a/src/ast/identifier_expression.h
+++ b/src/ast/identifier_expression.h
@@ -83,10 +83,11 @@ class IdentifierExpression : public Castable<IdentifierExpression, Expression> {
  private:
   IdentifierExpression(const IdentifierExpression&) = delete;
 
-  Intrinsic intrinsic_ = Intrinsic::kNone;
-  std::unique_ptr<intrinsic::Signature> intrinsic_sig_;
-  Symbol sym_;
-  std::string name_;
+  Symbol const sym_;
+  std::string const name_;
+
+  Intrinsic intrinsic_ = Intrinsic::kNone;               // Semantic info
+  std::unique_ptr<intrinsic::Signature> intrinsic_sig_;  // Semantic info
 };
 
 }  // namespace ast
diff --git a/src/ast/if_statement.h b/src/ast/if_statement.h
index f489c4a930..11515abd57 100644
--- a/src/ast/if_statement.h
+++ b/src/ast/if_statement.h
@@ -51,8 +51,6 @@ class IfStatement : public Castable<IfStatement, Statement> {
 
   /// @returns the else statements
   const ElseStatementList& else_statements() const { return else_statements_; }
-  /// @returns the else statements
-  ElseStatementList& else_statements() { return else_statements_; }
 
   /// @returns true if there are else statements
   bool has_else_statements() const { return !else_statements_.empty(); }
@@ -76,9 +74,9 @@ class IfStatement : public Castable<IfStatement, Statement> {
  private:
   IfStatement(const IfStatement&) = delete;
 
-  Expression* condition_ = nullptr;
-  BlockStatement* body_ = nullptr;
-  ElseStatementList else_statements_;
+  Expression* const condition_;
+  BlockStatement* const body_;
+  ElseStatementList const else_statements_;
 };
 
 }  // namespace ast
diff --git a/src/ast/literal.h b/src/ast/literal.h
index dea8a63563..f5127ef11a 100644
--- a/src/ast/literal.h
+++ b/src/ast/literal.h
@@ -52,7 +52,7 @@ class Literal : public Castable<Literal, Node> {
   explicit Literal(const Source& source, type::Type* type);
 
  private:
-  type::Type* type_ = nullptr;
+  type::Type* const type_;
 };
 
 }  // namespace ast
diff --git a/src/ast/location_decoration.h b/src/ast/location_decoration.h
index f6583ea326..fc2496369d 100644
--- a/src/ast/location_decoration.h
+++ b/src/ast/location_decoration.h
@@ -49,7 +49,7 @@ class LocationDecoration
   LocationDecoration* Clone(CloneContext* ctx) const override;
 
  private:
-  uint32_t value_;
+  uint32_t const value_;
 };
 
 }  // namespace ast
diff --git a/src/ast/loop_statement.h b/src/ast/loop_statement.h
index 6eb4b392b8..e80eb943b2 100644
--- a/src/ast/loop_statement.h
+++ b/src/ast/loop_statement.h
@@ -71,8 +71,8 @@ class LoopStatement : public Castable<LoopStatement, Statement> {
  private:
   LoopStatement(const LoopStatement&) = delete;
 
-  BlockStatement* body_ = nullptr;
-  BlockStatement* continuing_ = nullptr;
+  BlockStatement* const body_;
+  BlockStatement* const continuing_;
 };
 
 }  // namespace ast
diff --git a/src/ast/member_accessor_expression.h b/src/ast/member_accessor_expression.h
index 982fc66c3d..d9aef791e9 100644
--- a/src/ast/member_accessor_expression.h
+++ b/src/ast/member_accessor_expression.h
@@ -64,8 +64,8 @@ class MemberAccessorExpression
  private:
   MemberAccessorExpression(const MemberAccessorExpression&) = delete;
 
-  Expression* struct_ = nullptr;
-  IdentifierExpression* member_ = nullptr;
+  Expression* const struct_;
+  IdentifierExpression* const member_;
 };
 
 }  // namespace ast
diff --git a/src/ast/node.h b/src/ast/node.h
index b4f6120ef0..b3d5cdee28 100644
--- a/src/ast/node.h
+++ b/src/ast/node.h
@@ -75,7 +75,7 @@ class Node : public Castable<Node> {
  private:
   Node(const Node&) = delete;
 
-  Source source_;
+  Source const source_;
 };
 
 }  // namespace ast
diff --git a/src/ast/return_statement.cc b/src/ast/return_statement.cc
index 3583138bbe..93f9b4fb88 100644
--- a/src/ast/return_statement.cc
+++ b/src/ast/return_statement.cc
@@ -22,7 +22,8 @@ TINT_INSTANTIATE_CLASS_ID(tint::ast::ReturnStatement);
 namespace tint {
 namespace ast {
 
-ReturnStatement::ReturnStatement(const Source& source) : Base(source) {}
+ReturnStatement::ReturnStatement(const Source& source)
+    : Base(source), value_(nullptr) {}
 
 ReturnStatement::ReturnStatement(const Source& source, Expression* value)
     : Base(source), value_(value) {}
diff --git a/src/ast/return_statement.h b/src/ast/return_statement.h
index 8b00e2a000..5a56ba6a55 100644
--- a/src/ast/return_statement.h
+++ b/src/ast/return_statement.h
@@ -62,7 +62,7 @@ class ReturnStatement : public Castable<ReturnStatement, Statement> {
  private:
   ReturnStatement(const ReturnStatement&) = delete;
 
-  Expression* value_ = nullptr;
+  Expression* const value_;
 };
 
 }  // namespace ast
diff --git a/src/ast/scalar_constructor_expression.h b/src/ast/scalar_constructor_expression.h
index ee7e835f02..5c96ef9b3a 100644
--- a/src/ast/scalar_constructor_expression.h
+++ b/src/ast/scalar_constructor_expression.h
@@ -58,7 +58,7 @@ class ScalarConstructorExpression
  private:
   ScalarConstructorExpression(const ScalarConstructorExpression&) = delete;
 
-  Literal* literal_ = nullptr;
+  Literal* const literal_;
 };
 
 }  // namespace ast
diff --git a/src/ast/set_decoration.h b/src/ast/set_decoration.h
index 1ea07b2041..ec97a32535 100644
--- a/src/ast/set_decoration.h
+++ b/src/ast/set_decoration.h
@@ -48,7 +48,7 @@ class SetDecoration : public Castable<SetDecoration, VariableDecoration> {
   SetDecoration* Clone(CloneContext* ctx) const override;
 
  private:
-  uint32_t value_;
+  uint32_t const value_;
 };
 
 }  // namespace ast
diff --git a/src/ast/sint_literal.h b/src/ast/sint_literal.h
index cf4ac57730..2df717df91 100644
--- a/src/ast/sint_literal.h
+++ b/src/ast/sint_literal.h
@@ -50,7 +50,7 @@ class SintLiteral : public Castable<SintLiteral, IntLiteral> {
   SintLiteral* Clone(CloneContext* ctx) const override;
 
  private:
-  int32_t value_;
+  int32_t const value_;
 };
 
 }  // namespace ast
diff --git a/src/ast/stage_decoration.h b/src/ast/stage_decoration.h
index a8ee49ff5f..4208c7da16 100644
--- a/src/ast/stage_decoration.h
+++ b/src/ast/stage_decoration.h
@@ -47,7 +47,7 @@ class StageDecoration : public Castable<StageDecoration, FunctionDecoration> {
   StageDecoration* Clone(CloneContext* ctx) const override;
 
  private:
-  PipelineStage stage_ = PipelineStage::kNone;
+  PipelineStage const stage_;
 };
 
 }  // namespace ast
diff --git a/src/ast/stride_decoration.h b/src/ast/stride_decoration.h
index dc8997826e..ad9977833d 100644
--- a/src/ast/stride_decoration.h
+++ b/src/ast/stride_decoration.h
@@ -48,7 +48,7 @@ class StrideDecoration : public Castable<StrideDecoration, ArrayDecoration> {
   StrideDecoration* Clone(CloneContext* ctx) const override;
 
  private:
-  uint32_t stride_;
+  uint32_t const stride_;
 };
 
 }  // namespace ast
diff --git a/src/ast/struct.h b/src/ast/struct.h
index 36e78ba5fb..260bfb6e5f 100644
--- a/src/ast/struct.h
+++ b/src/ast/struct.h
@@ -74,8 +74,8 @@ class Struct : public Castable<Struct, Node> {
  private:
   Struct(const Struct&) = delete;
 
-  StructMemberList members_;
-  StructDecorationList decorations_;
+  StructMemberList const members_;
+  StructDecorationList const decorations_;
 };
 
 }  // namespace ast
diff --git a/src/ast/struct_member.h b/src/ast/struct_member.h
index 73470b6e04..fb72fb1023 100644
--- a/src/ast/struct_member.h
+++ b/src/ast/struct_member.h
@@ -77,9 +77,9 @@ class StructMember : public Castable<StructMember, Node> {
  private:
   StructMember(const StructMember&) = delete;
 
-  std::string name_;
-  type::Type* type_ = nullptr;
-  StructMemberDecorationList decorations_;
+  std::string const name_;
+  type::Type* const type_;
+  StructMemberDecorationList const decorations_;
 };
 
 /// A list of struct members
diff --git a/src/ast/struct_member_offset_decoration.h b/src/ast/struct_member_offset_decoration.h
index 001d777ff8..445483b891 100644
--- a/src/ast/struct_member_offset_decoration.h
+++ b/src/ast/struct_member_offset_decoration.h
@@ -49,7 +49,7 @@ class StructMemberOffsetDecoration
   StructMemberOffsetDecoration* Clone(CloneContext* ctx) const override;
 
  private:
-  uint32_t offset_;
+  uint32_t const offset_;
 };
 
 }  // namespace ast
diff --git a/src/ast/switch_statement.h b/src/ast/switch_statement.h
index 917d6aada8..b964724746 100644
--- a/src/ast/switch_statement.h
+++ b/src/ast/switch_statement.h
@@ -45,8 +45,6 @@ class SwitchStatement : public Castable<SwitchStatement, Statement> {
   /// @returns true if this is a default statement
   bool IsDefault() const { return condition_ == nullptr; }
 
-  /// @returns the Switch body
-  CaseStatementList& body() { return body_; }
   /// @returns the Switch body
   const CaseStatementList& body() const { return body_; }
 
@@ -69,8 +67,8 @@ class SwitchStatement : public Castable<SwitchStatement, Statement> {
  private:
   SwitchStatement(const SwitchStatement&) = delete;
 
-  Expression* condition_ = nullptr;
-  CaseStatementList body_;
+  Expression* const condition_;
+  CaseStatementList const body_;
 };
 
 }  // namespace ast
diff --git a/src/ast/type/access_control_type.h b/src/ast/type/access_control_type.h
index bffd44e6f0..e018b95a9b 100644
--- a/src/ast/type/access_control_type.h
+++ b/src/ast/type/access_control_type.h
@@ -66,8 +66,8 @@ class AccessControl : public Castable<AccessControl, Type> {
   AccessControl* Clone(CloneContext* ctx) const override;
 
  private:
-  ast::AccessControl access_ = ast::AccessControl::kReadOnly;
-  Type* subtype_ = nullptr;
+  ast::AccessControl const access_;
+  Type* const subtype_;
 };
 
 }  // namespace type
diff --git a/src/ast/type/alias_type.h b/src/ast/type/alias_type.h
index 2fcd45c30a..d90a99eba6 100644
--- a/src/ast/type/alias_type.h
+++ b/src/ast/type/alias_type.h
@@ -63,9 +63,9 @@ class Alias : public Castable<Alias, Type> {
   Alias* Clone(CloneContext* ctx) const override;
 
  private:
-  Symbol symbol_;
-  std::string name_;
-  Type* subtype_ = nullptr;
+  Symbol const symbol_;
+  std::string const name_;
+  Type* const subtype_;
 };
 
 }  // namespace type
diff --git a/src/ast/type/array_type.h b/src/ast/type/array_type.h
index a120a46d77..eafb2048e8 100644
--- a/src/ast/type/array_type.h
+++ b/src/ast/type/array_type.h
@@ -76,9 +76,9 @@ class Array : public Castable<Array, Type> {
   Array* Clone(CloneContext* ctx) const override;
 
  private:
-  Type* subtype_ = nullptr;
-  uint32_t size_ = 0;
-  ArrayDecorationList decos_;
+  Type* const subtype_;
+  uint32_t const size_;
+  ArrayDecorationList const decos_;
 };
 
 }  // namespace type
diff --git a/src/ast/type/matrix_type.h b/src/ast/type/matrix_type.h
index ef39c1ac89..500f43eb83 100644
--- a/src/ast/type/matrix_type.h
+++ b/src/ast/type/matrix_type.h
@@ -61,9 +61,9 @@ class Matrix : public Castable<Matrix, Type> {
   Matrix* Clone(CloneContext* ctx) const override;
 
  private:
-  Type* subtype_ = nullptr;
-  uint32_t rows_ = 2;
-  uint32_t columns_ = 2;
+  Type* const subtype_;
+  uint32_t const rows_;
+  uint32_t const columns_;
 };
 
 }  // namespace type
diff --git a/src/ast/type/multisampled_texture_type.h b/src/ast/type/multisampled_texture_type.h
index cdbfdb4776..4fb45e2577 100644
--- a/src/ast/type/multisampled_texture_type.h
+++ b/src/ast/type/multisampled_texture_type.h
@@ -46,7 +46,7 @@ class MultisampledTexture : public Castable<MultisampledTexture, Texture> {
   MultisampledTexture* Clone(CloneContext* ctx) const override;
 
  private:
-  Type* type_ = nullptr;
+  Type* const type_;
 };
 
 }  // namespace type
diff --git a/src/ast/type/pointer_type.h b/src/ast/type/pointer_type.h
index b22b130521..7a9a61b4c8 100644
--- a/src/ast/type/pointer_type.h
+++ b/src/ast/type/pointer_type.h
@@ -50,8 +50,8 @@ class Pointer : public Castable<Pointer, Type> {
   Pointer* Clone(CloneContext* ctx) const override;
 
  private:
-  Type* subtype_;
-  StorageClass storage_class_;
+  Type* const subtype_;
+  StorageClass const storage_class_;
 };
 
 }  // namespace type
diff --git a/src/ast/type/sampled_texture_type.h b/src/ast/type/sampled_texture_type.h
index 54d9da4b42..cdc93fa6bb 100644
--- a/src/ast/type/sampled_texture_type.h
+++ b/src/ast/type/sampled_texture_type.h
@@ -46,7 +46,7 @@ class SampledTexture : public Castable<SampledTexture, Texture> {
   SampledTexture* Clone(CloneContext* ctx) const override;
 
  private:
-  Type* type_ = nullptr;
+  Type* const type_;
 };
 
 }  // namespace type
diff --git a/src/ast/type/sampler_type.h b/src/ast/type/sampler_type.h
index 4e71fbbc34..28a60e8faf 100644
--- a/src/ast/type/sampler_type.h
+++ b/src/ast/type/sampler_type.h
@@ -58,7 +58,7 @@ class Sampler : public Castable<Sampler, Type> {
   Sampler* Clone(CloneContext* ctx) const override;
 
  private:
-  SamplerKind kind_ = SamplerKind::kSampler;
+  SamplerKind const kind_;
 };
 
 }  // namespace type
diff --git a/src/ast/type/storage_texture_type.h b/src/ast/type/storage_texture_type.h
index 9f88b4d825..33e18159b5 100644
--- a/src/ast/type/storage_texture_type.h
+++ b/src/ast/type/storage_texture_type.h
@@ -101,9 +101,10 @@ class StorageTexture : public Castable<StorageTexture, Texture> {
   StorageTexture* Clone(CloneContext* ctx) const override;
 
  private:
-  Type* type_ = nullptr;
-  ast::AccessControl access_ = ast::AccessControl::kReadOnly;
-  ImageFormat image_format_ = ImageFormat::kRgba32Float;
+  ast::AccessControl const access_;
+  ImageFormat const image_format_;
+
+  Type* type_ = nullptr;  // Semantic info
 };
 
 }  // namespace type
diff --git a/src/ast/type/struct_type.h b/src/ast/type/struct_type.h
index d372c1c129..d1a939c4ac 100644
--- a/src/ast/type/struct_type.h
+++ b/src/ast/type/struct_type.h
@@ -68,9 +68,9 @@ class Struct : public Castable<Struct, Type> {
   Struct* Clone(CloneContext* ctx) const override;
 
  private:
-  Symbol symbol_;
-  std::string name_;
-  ast::Struct* struct_ = nullptr;
+  Symbol const symbol_;
+  std::string const name_;
+  ast::Struct* const struct_;
 
   uint64_t LargestMemberBaseAlignment(MemoryLayout mem_layout) const;
 };
diff --git a/src/ast/type/texture_type.h b/src/ast/type/texture_type.h
index ccac6de667..88af3fa3ef 100644
--- a/src/ast/type/texture_type.h
+++ b/src/ast/type/texture_type.h
@@ -56,7 +56,7 @@ class Texture : public Castable<Texture, Type> {
   TextureDimension dim() const { return dim_; }
 
  private:
-  TextureDimension dim_ = TextureDimension::k1d;
+  TextureDimension const dim_;
 };
 
 }  // namespace type
diff --git a/src/ast/type/vector_type.h b/src/ast/type/vector_type.h
index 9634f43232..4228c59a06 100644
--- a/src/ast/type/vector_type.h
+++ b/src/ast/type/vector_type.h
@@ -58,8 +58,8 @@ class Vector : public Castable<Vector, Type> {
   Vector* Clone(CloneContext* ctx) const override;
 
  private:
-  Type* subtype_ = nullptr;
-  uint32_t size_ = 2;
+  Type* const subtype_;
+  uint32_t const size_;
 };
 
 }  // namespace type
diff --git a/src/ast/type_constructor_expression.h b/src/ast/type_constructor_expression.h
index 3863adca60..66f45b1d29 100644
--- a/src/ast/type_constructor_expression.h
+++ b/src/ast/type_constructor_expression.h
@@ -63,8 +63,8 @@ class TypeConstructorExpression
  private:
   TypeConstructorExpression(const TypeConstructorExpression&) = delete;
 
-  type::Type* type_ = nullptr;
-  ExpressionList values_;
+  type::Type* const type_;
+  ExpressionList const values_;
 };
 
 }  // namespace ast
diff --git a/src/ast/uint_literal.h b/src/ast/uint_literal.h
index 9010b6d593..3464a88d0d 100644
--- a/src/ast/uint_literal.h
+++ b/src/ast/uint_literal.h
@@ -50,7 +50,7 @@ class UintLiteral : public Castable<UintLiteral, IntLiteral> {
   UintLiteral* Clone(CloneContext* ctx) const override;
 
  private:
-  uint32_t value_;
+  uint32_t const value_;
 };
 
 }  // namespace ast
diff --git a/src/ast/unary_op_expression.h b/src/ast/unary_op_expression.h
index 5ec3dcf5a0..0a9d352643 100644
--- a/src/ast/unary_op_expression.h
+++ b/src/ast/unary_op_expression.h
@@ -61,8 +61,8 @@ class UnaryOpExpression : public Castable<UnaryOpExpression, Expression> {
  private:
   UnaryOpExpression(const UnaryOpExpression&) = delete;
 
-  UnaryOp op_ = UnaryOp::kNegation;
-  Expression* expr_ = nullptr;
+  UnaryOp const op_;
+  Expression* const expr_;
 };
 
 }  // namespace ast
diff --git a/src/ast/variable.cc b/src/ast/variable.cc
index e31b02e2f1..c94a97d6b5 100644
--- a/src/ast/variable.cc
+++ b/src/ast/variable.cc
@@ -34,11 +34,11 @@ Variable::Variable(const Source& source,
                    VariableDecorationList decorations)
     : Base(source),
       name_(name),
-      storage_class_(sc),
       type_(type),
       is_const_(is_const),
       constructor_(constructor),
-      decorations_(std::move(decorations)) {}
+      decorations_(std::move(decorations)),
+      storage_class_(sc) {}
 
 Variable::Variable(Variable&&) = default;
 
diff --git a/src/ast/variable.h b/src/ast/variable.h
index b15d222aff..bf8c1db837 100644
--- a/src/ast/variable.h
+++ b/src/ast/variable.h
@@ -162,13 +162,14 @@ class Variable : public Castable<Variable, Node> {
  private:
   Variable(const Variable&) = delete;
 
-  std::string name_;
-  StorageClass storage_class_ = StorageClass::kNone;
+  std::string const name_;
   // The value type if a const or formal paramter, and the store type if a var
-  type::Type* type_ = nullptr;
-  bool is_const_ = false;
-  Expression* constructor_ = nullptr;
-  VariableDecorationList decorations_;
+  type::Type* const type_;
+  bool const is_const_;
+  Expression* const constructor_;
+  VariableDecorationList const decorations_;
+
+  StorageClass storage_class_ = StorageClass::kNone;  // Semantic info
 };
 
 /// A list of variables
diff --git a/src/ast/variable_decl_statement.h b/src/ast/variable_decl_statement.h
index 88bef800c4..bc2bed7622 100644
--- a/src/ast/variable_decl_statement.h
+++ b/src/ast/variable_decl_statement.h
@@ -59,7 +59,7 @@ class VariableDeclStatement
  private:
   VariableDeclStatement(const VariableDeclStatement&) = delete;
 
-  Variable* variable_ = nullptr;
+  Variable* const variable_;
 };
 
 }  // namespace ast
diff --git a/src/ast/workgroup_decoration.cc b/src/ast/workgroup_decoration.cc
index 63fdf20b89..1e0e5d0b36 100644
--- a/src/ast/workgroup_decoration.cc
+++ b/src/ast/workgroup_decoration.cc
@@ -23,12 +23,12 @@ namespace tint {
 namespace ast {
 
 WorkgroupDecoration::WorkgroupDecoration(const Source& source, uint32_t x)
-    : Base(source), x_(x) {}
+    : WorkgroupDecoration(source, x, 1, 1) {}
 
 WorkgroupDecoration::WorkgroupDecoration(const Source& source,
                                          uint32_t x,
                                          uint32_t y)
-    : Base(source), x_(x), y_(y) {}
+    : WorkgroupDecoration(source, x, y, 1) {}
 
 WorkgroupDecoration::WorkgroupDecoration(const Source& source,
                                          uint32_t x,
diff --git a/src/ast/workgroup_decoration.h b/src/ast/workgroup_decoration.h
index 9946108620..d39421513d 100644
--- a/src/ast/workgroup_decoration.h
+++ b/src/ast/workgroup_decoration.h
@@ -64,9 +64,9 @@ class WorkgroupDecoration
   WorkgroupDecoration* Clone(CloneContext* ctx) const override;
 
  private:
-  uint32_t x_ = 1;
-  uint32_t y_ = 1;
-  uint32_t z_ = 1;
+  uint32_t const x_;
+  uint32_t const y_;
+  uint32_t const z_;
 };
 
 }  // namespace ast