diff --git a/packages/api-observable/src/classes.ts b/packages/api-observable/src/classes.ts
index 568e9dad395a..5111438c322a 100644
--- a/packages/api-observable/src/classes.ts
+++ b/packages/api-observable/src/classes.ts
@@ -16,15 +16,15 @@ export class RxProposal extends Struct.with({ id: PropIndex, proposal: Proposal,
   }
 
   get address (): AccountId {
-    return this.raw.address as AccountId;
+    return this.get('address') as AccountId;
   }
 
   get id (): PropIndex {
-    return this.raw.id as PropIndex;
+    return this.get('id') as PropIndex;
   }
 
   get proposal (): Proposal {
-    return this.raw.proposal as Proposal;
+    return this.get('proposal') as Proposal;
   }
 }
 
@@ -37,11 +37,11 @@ export class RxProposalDeposits extends Struct.with({ balance: Balance, addresse
   }
 
   get addresses (): Vector<AccountId> {
-    return this.raw.addresses as Vector<AccountId>;
+    return this.get('addresses') as Vector<AccountId>;
   }
 
   get balance (): Balance {
-    return this.raw.balance as Balance;
+    return this.get('balance') as Balance;
   }
 }
 
@@ -56,18 +56,18 @@ export class RxReferendum extends Struct.with({ blockNumber: BlockNumber, propos
   }
 
   get blockNumber (): BlockNumber {
-    return this.raw.blockNumber as BlockNumber;
+    return this.get('blockNumber') as BlockNumber;
   }
 
   get id (): ReferendumIndex {
-    return this.raw.id as ReferendumIndex;
+    return this.get('id') as ReferendumIndex;
   }
 
   get proposal (): Proposal {
-    return this.raw.proposal as Proposal;
+    return this.get('proposal') as Proposal;
   }
 
   get voteThreshold (): VoteThreshold {
-    return this.raw.voteThreshold as VoteThreshold;
+    return this.get('voteThreshold') as VoteThreshold;
   }
 }
diff --git a/packages/types/src/Bft.ts b/packages/types/src/Bft.ts
index 0bafa9305db8..77f376ea05fa 100644
--- a/packages/types/src/Bft.ts
+++ b/packages/types/src/Bft.ts
@@ -28,11 +28,11 @@ export class BftAuthoritySignature extends Tuple {
   }
 
   get authorityId (): AuthorityId {
-    return this.raw.authorityId as AuthorityId;
+    return this.getAtIndex(0) as AuthorityId;
   }
 
   get signature (): Signature {
-    return this.raw.signature as Signature;
+    return this.getAtIndex(1) as Signature;
   }
 }
 
@@ -52,11 +52,11 @@ export class BftHashSignature extends Tuple {
   }
 
   get hash (): Hash {
-    return this.raw.hash as Hash;
+    return this.getAtIndex(0) as Hash;
   }
 
   get signature (): Signature {
-    return this.raw.signature as Signature;
+    return this.getAtIndex(1) as Signature;
   }
 }
 
@@ -78,14 +78,14 @@ export class Justification extends Struct {
   }
 
   get hash (): Hash {
-    return this.raw.hash as Hash;
+    return this.get('hash') as Hash;
   }
 
   get round (): U32 {
-    return this.raw.round as U32;
+    return this.get('round') as U32;
   }
 
   get signatures (): Vector<BftAuthoritySignature> {
-    return this.raw.signatures as Vector<BftAuthoritySignature>;
+    return this.get('signatures') as Vector<BftAuthoritySignature>;
   }
 }
diff --git a/packages/types/src/Block.ts b/packages/types/src/Block.ts
index 99a30f680b2f..3535435c1507 100644
--- a/packages/types/src/Block.ts
+++ b/packages/types/src/Block.ts
@@ -26,7 +26,7 @@ export default class Block extends Struct {
   }
 
   get extrinsics (): Extrinsics {
-    return this.raw.extrinsics as Extrinsics;
+    return this.get('extrinsics') as Extrinsics;
   }
 
   // convenience, encodes the header and returns the actual hash
@@ -37,6 +37,6 @@ export default class Block extends Struct {
   }
 
   get header (): Header {
-    return this.raw.header as Header;
+    return this.get('header') as Header;
   }
 }
diff --git a/packages/types/src/Extrinsic.ts b/packages/types/src/Extrinsic.ts
index b8656cd5e97c..5a08f885f39b 100644
--- a/packages/types/src/Extrinsic.ts
+++ b/packages/types/src/Extrinsic.ts
@@ -94,11 +94,11 @@ export default class Extrinsic extends Struct {
   }
 
   get method (): Method {
-    return this.raw.method as Method;
+    return this.get('method') as Method;
   }
 
   get signature (): ExtrinsicSignature {
-    return this.raw.signature as ExtrinsicSignature;
+    return this.get('signature') as ExtrinsicSignature;
   }
 
   get encodedLength (): number {
diff --git a/packages/types/src/ExtrinsicSignature.ts b/packages/types/src/ExtrinsicSignature.ts
index 92d91c491fe1..6549b7441a67 100644
--- a/packages/types/src/ExtrinsicSignature.ts
+++ b/packages/types/src/ExtrinsicSignature.ts
@@ -74,19 +74,19 @@ export default class ExtrinsicSignature extends Struct {
   }
 
   get era (): ExtrinsicEra {
-    return this.raw.era as ExtrinsicEra;
+    return this.get('era') as ExtrinsicEra;
   }
 
   get nonce (): Nonce {
-    return this.raw.nonce as Nonce;
+    return this.get('nonce') as Nonce;
   }
 
   get signature (): Signature {
-    return this.raw.signature as Signature;
+    return this.get('signature') as Signature;
   }
 
   get signer (): Address {
-    return this.raw.signer as Address;
+    return this.get('signer') as Address;
   }
 
   get version (): number {
@@ -112,10 +112,10 @@ export default class ExtrinsicSignature extends Struct {
     });
     const signature = new Signature(signingPayload.sign(signerPair));
 
-    this.raw.era = signingPayload.era;
-    this.raw.nonce = signingPayload.nonce;
-    this.raw.signer = signer;
-    this.raw.signature = signature;
+    this.set('era', signingPayload.era);
+    this.set('nonce', signingPayload.nonce);
+    this.set('signer', signer);
+    this.set('signature', signature);
 
     return this;
   }
diff --git a/packages/types/src/Header.ts b/packages/types/src/Header.ts
index 7a0c1a965675..811097780ae4 100644
--- a/packages/types/src/Header.ts
+++ b/packages/types/src/Header.ts
@@ -36,7 +36,7 @@ export class Digest extends Struct {
   }
 
   get logs (): Vector<Bytes> {
-    return this.raw.logs as Vector<Bytes>;
+    return this.get('logs') as Vector<Bytes>;
   }
 }
 
@@ -53,15 +53,15 @@ export default class Header extends Struct {
   }
 
   get blockNumber (): BlockNumber {
-    return this.raw.number as BlockNumber;
+    return this.get('number') as BlockNumber;
   }
 
   get digest (): Digest {
-    return this.raw.digest as Digest;
+    return this.get('digest') as Digest;
   }
 
   get extrinsicsRoot (): Hash {
-    return this.raw.extrinsicsRoot as Hash;
+    return this.get('extrinsicsRoot') as Hash;
   }
 
   // convenience, encodes the header and returns the actual hash
@@ -72,10 +72,10 @@ export default class Header extends Struct {
   }
 
   get parentHash (): Hash {
-    return this.raw.parentHash as Hash;
+    return this.get('parentHash') as Hash;
   }
 
   get stateRoot (): Hash {
-    return this.raw.stateRoot as Hash;
+    return this.get('stateRoot') as Hash;
   }
 }
diff --git a/packages/types/src/KeyValue.ts b/packages/types/src/KeyValue.ts
index a911d63ba5ee..e7f777af4003 100644
--- a/packages/types/src/KeyValue.ts
+++ b/packages/types/src/KeyValue.ts
@@ -28,11 +28,11 @@ export default class KeyValue extends Struct {
   }
 
   get key (): StorageKey {
-    return this.raw.key as StorageKey;
+    return this.get('key') as StorageKey;
   }
 
   get value (): StorageData {
-    return this.raw.value as StorageData;
+    return this.get('value') as StorageData;
   }
 }
 
@@ -53,10 +53,10 @@ export class KeyValueOption extends Tuple {
   }
 
   get key (): StorageKey {
-    return this.raw.key as StorageKey;
+    return this.getAtIndex(0) as StorageKey;
   }
 
   get value (): Option<StorageData> {
-    return this.raw.value as Option<StorageData>;
+    return this.getAtIndex(1) as Option<StorageData>;
   }
 }
diff --git a/packages/types/src/Metadata.ts b/packages/types/src/Metadata.ts
index 845b1a14f8cf..a9cdb8dadb14 100644
--- a/packages/types/src/Metadata.ts
+++ b/packages/types/src/Metadata.ts
@@ -32,15 +32,15 @@ export class OuterDispatchCall extends Struct {
   }
 
   get index (): U16 {
-    return this.raw.index as U16;
+    return this.get('index') as U16;
   }
 
   get name (): Text {
-    return this.raw.name as Text;
+    return this.get('name') as Text;
   }
 
   get prefix (): Text {
-    return this.raw.prefix as Text;
+    return this.get('prefix') as Text;
   }
 }
 
@@ -53,11 +53,11 @@ export class OuterDispatchMetadata extends Struct {
   }
 
   get calls (): Vector<OuterDispatchCall> {
-    return this.raw.calls as Vector<OuterDispatchCall>;
+    return this.get('calls') as Vector<OuterDispatchCall>;
   }
 
   get name (): Text {
-    return this.raw.name as Text;
+    return this.get('name') as Text;
   }
 }
 
@@ -71,15 +71,15 @@ export class EventMetadata extends Struct {
   }
 
   get arguments (): Vector<Type> {
-    return this.raw.arguments as Vector<Type>;
+    return this.get('arguments') as Vector<Type>;
   }
 
   get documentation (): Vector<Text> {
-    return this.raw.documentation as Vector<Text>;
+    return this.get('documentation') as Vector<Text>;
   }
 
   get name (): Text {
-    return this.raw.name as Text;
+    return this.get('name') as Text;
   }
 }
 
@@ -109,11 +109,11 @@ export class OuterEventMetadata extends Struct {
   }
 
   get events (): Vector<OuterEventMetadataEvent> {
-    return this.raw.events as Vector<OuterEventMetadataEvent>;
+    return this.get('events') as Vector<OuterEventMetadataEvent>;
   }
 
   get name (): Text {
-    return this.raw.name as Text;
+    return this.get('name') as Text;
   }
 }
 
@@ -126,11 +126,11 @@ export class FunctionArgumentMetadata extends Struct {
   }
 
   get name (): Text {
-    return this.raw.name as Text;
+    return this.get('name') as Text;
   }
 
   get type (): Type {
-    return this.raw.type as Type;
+    return this.get('type') as Type;
   }
 }
 
@@ -145,19 +145,19 @@ export class FunctionMetadata extends Struct {
   }
 
   get arguments (): Vector<FunctionArgumentMetadata> {
-    return this.raw.arguments as Vector<FunctionArgumentMetadata>;
+    return this.get('arguments') as Vector<FunctionArgumentMetadata>;
   }
 
   get documentation (): Vector<Text> {
-    return this.raw.documentation as Vector<Text>;
+    return this.get('documentation') as Vector<Text>;
   }
 
   get id (): U16 {
-    return this.raw.id as U16;
+    return this.get('id') as U16;
   }
 
   get name (): Text {
-    return this.raw.name as Text;
+    return this.get('name') as Text;
   }
 }
 
@@ -170,11 +170,11 @@ export class CallMetadata extends Struct {
   }
 
   get functions (): Vector<FunctionMetadata> {
-    return this.raw.functions as Vector<FunctionMetadata>;
+    return this.get('functions') as Vector<FunctionMetadata>;
   }
 
   get name (): Text {
-    return this.raw.name as Text;
+    return this.get('name') as Text;
   }
 }
 
@@ -187,11 +187,11 @@ export class ModuleMetadata extends Struct {
   }
 
   get call (): CallMetadata {
-    return this.raw.call as CallMetadata;
+    return this.get('call') as CallMetadata;
   }
 
   get name (): Text {
-    return this.raw.name as Text;
+    return this.get('name') as Text;
   }
 }
 
@@ -210,11 +210,11 @@ export class StorageFunctionType$Map extends Struct {
   }
 
   get key (): Type {
-    return this.raw.type as Type;
+    return this.get('key') as Type;
   }
 
   get value (): Type {
-    return this.raw.value as Type;
+    return this.get('value') as Type;
   }
 }
 
@@ -263,19 +263,19 @@ export class StorageFunctionMetadata extends Struct {
   }
 
   get documentation (): Vector<Text> {
-    return this.raw.documentation as Vector<Text>;
+    return this.get('documentation') as Vector<Text>;
   }
 
   get name (): Text {
-    return this.raw.name as Text;
+    return this.get('name') as Text;
   }
 
   get modifier (): StorageFunctionModifier {
-    return this.raw.modifier as StorageFunctionModifier;
+    return this.get('modifier') as StorageFunctionModifier;
   }
 
   get type (): StorageFunctionType {
-    return this.raw.type as StorageFunctionType;
+    return this.get('type') as StorageFunctionType;
   }
 }
 
@@ -288,11 +288,11 @@ export class StorageMetadata extends Struct {
   }
 
   get functions (): Vector<StorageFunctionMetadata> {
-    return this.raw.functions as Vector<StorageFunctionMetadata>;
+    return this.get('functions') as Vector<StorageFunctionMetadata>;
   }
 
   get prefix (): Text {
-    return this.raw.prefix as Text;
+    return this.get('prefix') as Text;
   }
 }
 
@@ -306,15 +306,15 @@ export class RuntimeModuleMetadata extends Struct {
   }
 
   get module (): ModuleMetadata {
-    return this.raw.module as ModuleMetadata;
+    return this.get('module') as ModuleMetadata;
   }
 
   get prefix (): Text {
-    return this.raw.prefix as Text;
+    return this.get('prefix') as Text;
   }
 
   get storage (): StorageMetadata | undefined {
-    return (this.raw.storage as Option<StorageMetadata>).value;
+    return (this.get('storage') as Option<StorageMetadata>).value;
   }
 }
 
@@ -358,15 +358,15 @@ export default class RuntimeMetadata extends Struct {
   }
 
   get calls (): Vector<OuterDispatchCall> {
-    return (this.raw.outerDispatch as OuterDispatchMetadata).calls;
+    return (this.get('outerDispatch') as OuterDispatchMetadata).calls;
   }
 
   get events (): Vector<OuterEventMetadataEvent> {
-    return (this.raw.outerEvent as OuterEventMetadata).events;
+    return (this.get('outerEvent') as OuterEventMetadata).events;
   }
 
   get modules (): Vector<RuntimeModuleMetadata> {
-    return this.raw.modules as Vector<RuntimeModuleMetadata>;
+    return this.get('modules') as Vector<RuntimeModuleMetadata>;
   }
 
   // Helper to retrieve a list of all type that are found, sorted and de-deuplicated
diff --git a/packages/types/src/Method.ts b/packages/types/src/Method.ts
index 6ec31cf3053e..daab2a259c40 100644
--- a/packages/types/src/Method.ts
+++ b/packages/types/src/Method.ts
@@ -147,7 +147,8 @@ export default class Method extends Struct {
   }
 
   get args (): Array<Base> {
-    return (this.getAtIndex(1) as Struct<Base>).values();
+    // FIXME This should return a Struct instead of an Array
+    return [...(this.get('args') as Struct).values()];
   }
 
   get argsDef (): ArgsDef {
@@ -155,11 +156,11 @@ export default class Method extends Struct {
   }
 
   get callIndex (): Uint8Array {
-    return (this.getAtIndex(0) as MethodIndex).callIndex;
+    return (this.get('methodIndex') as MethodIndex).callIndex;
   }
 
   get data (): Uint8Array {
-    return (this.getAtIndex(1) as Struct<Base>).toU8a();
+    return (this.get('args') as Struct).toU8a();
   }
 
   get meta (): FunctionMetadata {
diff --git a/packages/types/src/MisbehaviorReport.ts b/packages/types/src/MisbehaviorReport.ts
index c1446538655c..aedcf1030217 100644
--- a/packages/types/src/MisbehaviorReport.ts
+++ b/packages/types/src/MisbehaviorReport.ts
@@ -34,15 +34,15 @@ export class BftAtReport extends Struct {
   }
 
   get a (): BftHashSignature {
-    return this.raw.a as BftHashSignature;
+    return this.get('a') as BftHashSignature;
   }
 
   get b (): BftHashSignature {
-    return this.raw.b as BftHashSignature;
+    return this.get('b') as BftHashSignature;
   }
 
   get round (): U32 {
-    return this.raw.round as U32;
+    return this.get('round') as U32;
   }
 }
 
@@ -80,18 +80,18 @@ export default class MisbehaviorReport extends Struct {
   }
 
   get misbehavior (): MisbehaviorKind {
-    return this.raw.misbehavior as MisbehaviorKind;
+    return this.get('misbehavior') as MisbehaviorKind;
   }
 
   get parentHash (): Hash {
-    return this.raw.parentHash as Hash;
+    return this.get('parentHash') as Hash;
   }
 
   get parentNumber (): BlockNumber {
-    return this.raw.parentNumber as BlockNumber;
+    return this.get('parentNumber') as BlockNumber;
   }
 
   get target (): AuthorityId {
-    return this.raw.target as AuthorityId;
+    return this.get('target') as AuthorityId;
   }
 }
diff --git a/packages/types/src/RuntimeVersion.ts b/packages/types/src/RuntimeVersion.ts
index 6d57f90933b0..2cf38745119c 100644
--- a/packages/types/src/RuntimeVersion.ts
+++ b/packages/types/src/RuntimeVersion.ts
@@ -31,11 +31,11 @@ class RuntimeVersionApi extends Tuple {
   }
 
   get id (): ApiId {
-    return this.raw.id as ApiId;
+    return this.getAtIndex(0) as ApiId;
   }
 
   get version (): U32 {
-    return this.raw.version as U32;
+    return this.getAtIndex(1) as U32;
   }
 }
 
@@ -67,26 +67,26 @@ export default class RuntimeVersion extends Struct {
   }
 
   get apis (): Vector<RuntimeVersionApi> {
-    return this.raw.apis as Vector<RuntimeVersionApi>;
+    return this.get('apis') as Vector<RuntimeVersionApi>;
   }
 
   get authoringVersion (): U32 {
-    return this.raw.authoringVersion as U32;
+    return this.get('authoringVersion') as U32;
   }
 
   get implName (): Text {
-    return this.raw.implName as Text;
+    return this.get('implName') as Text;
   }
 
   get implVersion (): U32 {
-    return this.raw.implVersion as U32;
+    return this.get('implVersion') as U32;
   }
 
   get specName (): Text {
-    return this.raw.specName as Text;
+    return this.get('specName') as Text;
   }
 
   get specVersion (): U32 {
-    return this.raw.specVersion as U32;
+    return this.get('specVersion') as U32;
   }
 }
diff --git a/packages/types/src/SignaturePayload.ts b/packages/types/src/SignaturePayload.ts
index 4d623b7b4af8..39052ea0efc9 100644
--- a/packages/types/src/SignaturePayload.ts
+++ b/packages/types/src/SignaturePayload.ts
@@ -40,19 +40,19 @@ export default class SignaturePayload extends Struct {
   }
 
   get blockHash (): Hash {
-    return this.raw.blockHash as Hash;
+    return this.get('blockHash') as Hash;
   }
 
   get method (): Method {
-    return this.raw.method as Method;
+    return this.get('method') as Method;
   }
 
   get era (): ExtrinsicEra {
-    return this.raw.era as ExtrinsicEra;
+    return this.get('era') as ExtrinsicEra;
   }
 
   get nonce (): Nonce {
-    return this.raw.nonce as Nonce;
+    return this.get('nonce') as Nonce;
   }
 
   get signature (): Uint8Array {
diff --git a/packages/types/src/SignedBlock.ts b/packages/types/src/SignedBlock.ts
index 8809b274f67f..3a5d890d9d13 100644
--- a/packages/types/src/SignedBlock.ts
+++ b/packages/types/src/SignedBlock.ts
@@ -20,10 +20,10 @@ export default class SignedBlock extends Struct {
   }
 
   get block (): Block {
-    return this.raw.block as Block;
+    return this.get('block') as Block;
   }
 
   get justification (): Justification {
-    return this.raw.justification as Justification;
+    return this.get('justification') as Justification;
   }
 }
diff --git a/packages/types/src/StorageChangeSet.ts b/packages/types/src/StorageChangeSet.ts
index 7ed8fb26e68b..c01f6e3000b9 100644
--- a/packages/types/src/StorageChangeSet.ts
+++ b/packages/types/src/StorageChangeSet.ts
@@ -25,10 +25,10 @@ export default class StorageChangeSet extends Struct {
   }
 
   get changes (): Vector<KeyValueOption> {
-    return this.raw.changes as Vector<KeyValueOption>;
+    return this.get('changes') as Vector<KeyValueOption>;
   }
 
   get hash (): Hash {
-    return this.raw.hash as Hash;
+    return this.get('hash') as Hash;
   }
 }
diff --git a/packages/types/src/ValidatorPrefs.ts b/packages/types/src/ValidatorPrefs.ts
index f22c508cf27b..867e904f513c 100644
--- a/packages/types/src/ValidatorPrefs.ts
+++ b/packages/types/src/ValidatorPrefs.ts
@@ -22,10 +22,10 @@ export default class ValidatorPrefs extends Struct {
   }
 
   get unstakeThreshold (): U32 {
-    return this.raw.unstakeThreshold as U32;
+    return this.get('unstakeThreshold') as U32;
   }
 
   get validatorPayment (): Balance {
-    return this.raw.validatorPayment as Balance;
+    return this.get('validatorPayment') as Balance;
   }
 }
diff --git a/packages/types/src/codec/Struct.spec.js b/packages/types/src/codec/Struct.spec.ts
similarity index 51%
rename from packages/types/src/codec/Struct.spec.js
rename to packages/types/src/codec/Struct.spec.ts
index 4cb43b7f71bd..9ff1271b03d7 100644
--- a/packages/types/src/codec/Struct.spec.js
+++ b/packages/types/src/codec/Struct.spec.ts
@@ -2,26 +2,27 @@
 // This software may be modified and distributed under the terms
 // of the ISC license. See the LICENSE file for details.
 
+import { CodecTo } from '../types';
 import Struct from './Struct';
 import Text from '../Text';
 import U32 from '../U32';
 import Vector from './Vector';
 
-const testDecode = (type, input) =>
+const testDecode = (type: string, input: any) =>
   it(`can decode from ${type}`, () => {
     const s = new Struct({
       foo: Text,
       bar: U32
     }, input);
-    expect(s.keys()).toEqual(['foo', 'bar']);
+    expect([...s.keys()]).toEqual(['foo', 'bar']);
     expect(
-      s.values().map((v) =>
+      [...s.values()].map((v) =>
         v.toString()
       )
     ).toEqual(['bazzing', '69']);
   });
 
-const testEncode = (to, expected) =>
+const testEncode = (to: CodecTo, expected: any) =>
   it(`can encode ${to}`, () => {
     const s = new Struct({
       foo: Text,
@@ -32,13 +33,26 @@ const testEncode = (to, expected) =>
 
 describe('Struct', () => {
 
+  testDecode('array', ['bazzing', 69]);
+  testDecode('hex', '0x1c62617a7a696e6745000000');
   testDecode('object', { foo: 'bazzing', bar: 69 });
   testDecode('Uint8Array', Uint8Array.from([28, 98, 97, 122, 122, 105, 110, 103, 69, 0, 0, 0]));
 
-  // testEncode('toHex', '0x1c62617a7a696e6745000000'); // FIXME Add this
+  testEncode('toHex', '0x1c62617a7a696e6745000000');
+  testEncode('toJSON', { foo: 'bazzing', bar: 69 });
   testEncode('toU8a', Uint8Array.from([28, 98, 97, 122, 122, 105, 110, 103, 69, 0, 0, 0]));
-  testEncode('toString', '{foo: bazzing, bar: 69}');
+  testEncode('toString', '{"foo":"bazzing","bar":69}');
 
+  it('decodes null', () => {
+    expect(
+      new (
+        Struct.with({
+          txt: Text,
+          u32: U32
+        })
+      )(null).toString()
+    ).toEqual('{}');
+  });
 
   it('decodes a more complicated type', () => {
     const s = new Struct({
@@ -46,8 +60,19 @@ describe('Struct', () => {
         bar: Text
       }))
     }, { foo: [{ bar: 1 }, { bar: 2 }] });
-    expect(s.toString()).toBe('{foo: [{bar: 1}, {bar: 2}]}');
-  })
+    expect(s.toString()).toBe('{"foo":[{"bar":"1"},{"bar":"2"}]}');
+  });
+
+  it('throws when it cannot decode', () => {
+    expect(
+      () => new (
+        Struct.with({
+          txt: Text,
+          u32: U32
+        })
+      )('ABC')
+    ).toThrowError(/Struct: cannot decode type/);
+  });
 
   it('provides a clean toString()', () => {
     expect(
@@ -57,7 +82,18 @@ describe('Struct', () => {
           u32: U32
         })
       )({ txt: 'foo', u32: 0x123456 }).toString()
-    ).toEqual(`{txt: foo, u32: 1193046}`);
+    ).toEqual('{"txt":"foo","u32":1193046}');
+  });
+
+  it('correctly encodes length', () => {
+    expect(
+      new (
+        Struct.with({
+          txt: Text,
+          u32: U32
+        })
+      )({ foo: 'bazzing', bar: 69 }).encodedLength
+    ).toEqual(5);
   });
 
   it('exposes the types', () => {
@@ -66,6 +102,10 @@ describe('Struct', () => {
         foo: Text,
         bar: Text,
         baz: U32
+      }, {
+        foo: 'foo',
+        bar: 'bar',
+        baz: 3
       }).Type
     ).toEqual({
       foo: 'Text',
@@ -74,17 +114,16 @@ describe('Struct', () => {
     });
   });
 
-  it('exposes the keys/values', () => {
-    const test = new Struct({
-      foo: Text,
-      bar: U32
-    }, { foo: 'bazzing', bar: 69 });
-
-    expect(test.keys()).toEqual(['foo', 'bar']);
+  it('gets the value at a particular index', () => {
     expect(
-      test.values().map((v) =>
-        v.toString()
-      )
-    ).toEqual(['bazzing', '69']);
+      new (
+        Struct.with({
+          txt: Text,
+          u32: U32
+        })
+      )({ txt: 'foo', u32: 1234 })
+        .getAtIndex(1)
+        .toString()
+    ).toEqual('1234');
   });
 });
diff --git a/packages/types/src/codec/Struct.ts b/packages/types/src/codec/Struct.ts
index 2e6c8f14640b..3f2b1853573a 100644
--- a/packages/types/src/codec/Struct.ts
+++ b/packages/types/src/codec/Struct.ts
@@ -2,10 +2,10 @@
 // This software may be modified and distributed under the terms
 // of the ISC license. See the LICENSE file for details.
 
-import { hexToU8a, isHex, isObject, isU8a, u8aConcat } from '@polkadot/util';
+import { hexToU8a, isHex, isObject, isU8a, u8aConcat, u8aToHex } from '@polkadot/util';
 
 import Base from './Base';
-import { Constructor } from '../types';
+import { Codec, Constructor, ConstructorDef } from '../types';
 
 // A Struct defines an Object with key/values - where the values are Base<T> values. It removes
 // a lot of repetition from the actual coding, define a structure type, pass it the key/Base<T>
@@ -14,34 +14,57 @@ import { Constructor } from '../types';
 // it needs to decoded in the specific defined order.
 export default class Struct<
   // The actual Class structure, i.e. key -> Class
-  S = { [index: string]: Constructor<Base> },
+  S extends ConstructorDef = ConstructorDef,
   // internal type, instance of classes mapped by key
-  T = { [K in keyof S]: Base },
+  T extends { [K in keyof S]: Base } = { [K in keyof S]: Base },
   // input values, mapped by key can be anything (construction)
-  V = { [K in keyof S]: any },
+  V extends { [K in keyof S]: any } = { [K in keyof S]: any },
   // type names, mapped by key, name of Class in S
-  E = { [K in keyof S]: string }
-  > extends Base<T> {
+  E extends { [K in keyof S]: string } = { [K in keyof S]: string }
+  > extends Map<keyof S, Base> implements Codec {
+  public raw: Map<keyof S, Base>; // FIXME Remove this once we convert all types out of Base
   protected _jsonMap: Map<keyof S, string>;
   protected _Types: E;
 
   constructor (Types: S, value: V | Array<any> = {} as V, jsonMap: Map<keyof S, string> = new Map()) {
+    const decoded = Struct.decodeStruct<S, V, T>(Types, value, jsonMap);
     super(
-      Struct.decodeStruct(Types, value, jsonMap)
+      Object.entries(decoded)
     );
 
     this._jsonMap = jsonMap;
-    this._Types = Object
-      .keys(Types)
+    this._Types = (Object
+      .keys(Types) as Array<keyof S>)
       .reduce((result: E, key) => {
-        // @ts-ignore Same as above, can't do a simple one, I'm missing something simple
         result[key] = Types[key].name;
 
         return result;
       }, {} as E);
+
+    // FIXME Remove this once we convert all types out of Base
+    this.raw = this;
   }
 
-  static decodeStruct<S, V, T> (Types: S, value: any, jsonMap: Map<keyof S, string>): T {
+  /**
+   * Decode input to pass into constructor.
+   *
+   * @param Types - Types definition.
+   * @param value - Value to decode, one of:
+   * - null
+   * - undefined
+   * - hex
+   * - Uint8Array
+   * - object with `{ key1: value1, key2: value2 }`, assuming `key1` and `key2`
+   * are also keys in `Types`
+   * - array with `[value1, value2]` assuming the array has the same length as
+   * `Object.keys(Types)`
+   * @param jsonMap
+   */
+  private static decodeStruct<
+    S extends ConstructorDef,
+    _,
+    T extends { [K in keyof S]: Base }
+    > (Types: S, value: any, jsonMap: Map<keyof S, string>): T {
     // l.debug(() => ['Struct.decode', { Types, value }]);
 
     if (isHex(value)) {
@@ -54,15 +77,14 @@ export default class Struct<
     // used to track at which index we are currently parsing in that array.
     let currentIndex = 0;
 
-    return Object
-      .keys(Types)
+    return (Object
+      .keys(Types) as Array<keyof S>)
       .reduce((raw: T, key, index) => {
         // The key in the JSON can be snake_case (or other cases), but in our
         // Types, result or any other maps, it's camelCase
         const jsonKey = (jsonMap.get(key as any) && !value[key]) ? jsonMap.get(key as any) : key;
 
         if (isU8a(value)) {
-          // @ts-ignore FIXME See below
           raw[key] = new Types[key](
             value.subarray(
               currentIndex
@@ -70,30 +92,17 @@ export default class Struct<
           );
 
           // Move the currentIndex forward
-          // @ts-ignore FIXME See below
           currentIndex += raw[key].encodedLength;
-          // @ts-ignore FIXME See below
-        } else if (value[jsonKey] instanceof Types[key]) {
-          // @ts-ignore FIXME See below
-          raw[key] = value[jsonKey];
-        } else if (Array.isArray(value) && value.length === Object.keys(Types).length) {
-          // @ts-ignore FIXME See below
-          raw[key] = new Types[key](
-            // @ts-ignore FIXME
-            value[index]
-          );
+        } else if (Array.isArray(value)) {
+          raw[key] = value[index] instanceof Types[key]
+            ? value[index]
+            : new Types[key](value[index]);
         } else if (isObject(value)) {
-          // @ts-ignore FIXME Ok, something weird is going on here or I just don't get it...
-          // it works, so ignore the checker, although it drives me batty. (It started when
-          // the [key in keyof T] was added, the idea is to provide better checks, which
-          // does backfire here, but works externally.)
-          raw[key] = new Types[key](
-            // @ts-ignore FIXME
-            value[jsonKey]
-          );
+          raw[key] = value[jsonKey as string] instanceof Types[key]
+            ? value[jsonKey as string]
+            : new Types[key](value[jsonKey as string]);
         } else {
-          // @ts-ignore FIXME
-          throw new Error(`Struct: cannot decode type "${Types[key].name}" with value "${value}".`);
+          throw new Error(`Struct: cannot decode type "${Types[key].name}" with value "${JSON.stringify(value)}".`);
         }
 
         return raw;
@@ -101,7 +110,7 @@ export default class Struct<
   }
 
   static with<
-    S = { [index: string]: Constructor<Base> }
+    S extends ConstructorDef
     > (Types: S): Constructor<Struct<S>> {
     return class extends Struct<S> {
       constructor (value?: any, jsonMap?: Map<keyof S, string>) {
@@ -115,48 +124,39 @@ export default class Struct<
   }
 
   get encodedLength (): number {
-    return Object.values(this.raw).reduce((length, entry) => {
+    return [...this.values()].reduce((length, entry) => {
       return length += entry.encodedLength;
     }, 0);
   }
 
   getAtIndex (index: number): Base {
-    return this.values()[index];
+    return [...this.values()][index];
+  }
+
+  toHex () {
+    return u8aToHex(this.toU8a());
   }
 
   toJSON (): any {
-    return Object.keys(this.raw).reduce((json, key) => {
-      const jsonKey = this._jsonMap.get(key as any) || key;
+    return [...this.keys()].reduce((json, key) => {
+      const jsonKey = this._jsonMap.get(key) || key;
 
-      // @ts-ignore as above...
-      json[jsonKey] = this.raw[key].toJSON();
+      const value = this.get(key);
+      json[jsonKey] = value && value.toJSON();
 
       return json;
     }, {} as any);
   }
 
-  keys (): Array<string> {
-    return Object.keys(this.raw);
+  toString () {
+    return JSON.stringify(this.toJSON());
   }
 
   toU8a (isBare?: boolean): Uint8Array {
     return u8aConcat(
-      ...Object.values(this.raw).map((entry) =>
+      ...[...this.values()].map((entry) =>
         entry.toU8a(isBare)
       )
     );
   }
-
-  toString (): string {
-    const data = Object.keys(this.raw).map((key) =>
-      // @ts-ignore as above...
-      `${key}: ${this.raw[key].toString()}`
-    ).join(', ');
-
-    return `{${data}}`;
-  }
-
-  values (): Array<Base> {
-    return Object.values(this.raw);
-  }
 }
diff --git a/packages/types/src/codec/Tuple.ts b/packages/types/src/codec/Tuple.ts
index 740afb9f2a71..51e59ea2556c 100644
--- a/packages/types/src/codec/Tuple.ts
+++ b/packages/types/src/codec/Tuple.ts
@@ -2,7 +2,7 @@
 // This software may be modified and distributed under the terms
 // of the ISC license. See the LICENSE file for details.
 
-import { AnyU8a, Constructor } from '../types';
+import { Constructor, ConstructorDef } from '../types';
 import Base from './Base';
 import Struct from './Struct';
 
@@ -11,32 +11,12 @@ import Struct from './Struct';
 // while the U8a encoding is handled in the same way as a Struct
 export default class Tuple<
   // S & T definitions maps to what we have in Struct (naming documented there)
-  S = { [index: string]: Constructor<Base> },
-  T = { [K in keyof S]: Base },
-  V = { [K in keyof S]: any }
+  S extends ConstructorDef = { [index: string]: Constructor<Base> },
+  T extends { [K in keyof S]: Base }= { [K in keyof S]: Base },
+  V extends { [K in keyof S]: any } = { [K in keyof S]: any }
   > extends Struct<S, T, V> {
-  constructor (Types: S, value?: V | AnyU8a, jsonMap?: Map<keyof S, string>) {
-    super(Types, Tuple.decodeTuple(Types, value), jsonMap);
-  }
-
-  static decodeTuple<S, V> (Types: S, value: V | AnyU8a): V {
-    // If the input is an array, we convert it to a map
-    if (Array.isArray(value)) {
-      return Object
-        .keys(Types)
-        .reduce((result, key, index) => {
-          // @ts-ignore FIXME these types are a headache
-          result[key] = value[index];
-          return result;
-        }, {} as V);
-    }
-
-    // Or else, just decode like a normal Struct
-    return value as V;
-  }
-
   static with<
-    S = { [index: string]: Constructor<Base> }
+    S extends ConstructorDef= { [index: string]: Constructor<Base> }
     > (Types: S): Constructor<Tuple<S>> {
     return class extends Tuple<S> {
       constructor (value?: any) {
@@ -46,7 +26,7 @@ export default class Tuple<
   }
 
   toJSON (): any {
-    return Object.values(this.raw).map((entry) =>
+    return [...this.values()].map((entry) =>
       entry.toJSON()
     );
   }
diff --git a/packages/types/src/codec/createType.ts b/packages/types/src/codec/createType.ts
index 2e1c52458c9b..1444de726fab 100644
--- a/packages/types/src/codec/createType.ts
+++ b/packages/types/src/codec/createType.ts
@@ -4,13 +4,12 @@
 
 import { assert } from '@polkadot/util';
 
+import { Constructor } from '../types';
 import Text from '../Text';
 import Base from './Base';
 import Tuple from './Tuple';
 import Vector from './Vector';
 
-type Constructor = { new (value?: any): Base };
-
 export enum TypeDefInfo {
   Plain,
   Tuple,
diff --git a/packages/types/src/types.d.ts b/packages/types/src/types.d.ts
index 5df0e807db6d..ec046177d4a5 100644
--- a/packages/types/src/types.d.ts
+++ b/packages/types/src/types.d.ts
@@ -5,12 +5,27 @@
 import BN from 'bn.js';
 import * as Classes from './index';
 
+import Base from './codec/Base';
 import { U8a, UInt } from './codec';
 
 export type AnyNumber = UInt | BN | Uint8Array | number | string;
 
 export type AnyU8a = U8a | Uint8Array | Array<number> | string;
 
+export interface Codec {
+  encodedLength: number;
+  toHex(): string
+  toJSON(): any;
+  toString(): string;
+  toU8a(isBare?: boolean): Uint8Array;
+}
+
+export type CodecTo = 'toHex' | 'toJSON' | 'toString' | 'toU8a'
+
 export type CodecTypes = keyof typeof Classes;
 
-export type Constructor<T> = { new(value?: any): T };
+export type Constructor<T = Base> = { new(value?: any): T };
+
+export type ConstructorDef<T = Base> = { [index: string]: Constructor<T> };
+
+export type TypeDef<T = Base> = { [index: string]: Base<T> };