ts: Allow adding types for AccountsCoder names (#764)

ts/src/coder/accounts.ts

@@ -11,28 +11,25 @@ export const ACCOUNT_DISCRIMINATOR_SIZE = 8;
 /**
  * Encodes and decodes account objects.
  */
-export class AccountsCoder {
+export class AccountsCoder<A extends string = string> {
   /**
    * Maps account type identifier to a layout.
    */
-  private accountLayouts: Map<string, Layout>;
+  private accountLayouts: Map<A, Layout>;
 
   public constructor(idl: Idl) {
     if (idl.accounts === undefined) {
       this.accountLayouts = new Map();
       return;
     }
-    const layouts: [string, Layout][] = idl.accounts.map((acc) => {
+    const layouts: [A, Layout][] = idl.accounts.map((acc) => {
-      return [acc.name, IdlCoder.typeDefLayout(acc, idl.types)];
+      return [acc.name as A, IdlCoder.typeDefLayout(acc, idl.types)];
     });
 
     this.accountLayouts = new Map(layouts);
   }
 
-  public async encode<T = any>(
+  public async encode<T = any>(accountName: A, account: T): Promise<Buffer> {
-    accountName: string,
-    account: T
-  ): Promise<Buffer> {
     const buffer = Buffer.alloc(1000); // TODO: use a tighter buffer.
     const layout = this.accountLayouts.get(accountName);
     if (!layout) {
@@ -44,7 +41,7 @@ export class AccountsCoder {
     return Buffer.concat([discriminator, accountData]);
   }
 
-  public decode<T = any>(accountName: string, ix: Buffer): T {
+  public decode<T = any>(accountName: A, ix: Buffer): T {
     // Chop off the discriminator before decoding.
     const data = ix.slice(8);
     const layout = this.accountLayouts.get(accountName);

ts/src/coder/index.ts

@@ -20,7 +20,7 @@ export { StateCoder, stateDiscriminator } from "./state";
 /**
  * Coder provides a facade for encoding and decoding all IDL related objects.
  */
-export default class Coder {
+export default class Coder<A extends string = string> {
   /**
    * Instruction coder.
    */
@@ -29,7 +29,7 @@ export default class Coder {
   /**
    * Account coder.
    */
-  readonly accounts: AccountsCoder;
+  readonly accounts: AccountsCoder<A>;
 
   /**
    * Types coder.