✨ 【第14章 学習用テストと回帰テスト】 為替レートを管理するオブジェクトを作成する

・ただし、USD → USD の変換がまだうまくいっていないので修正する必要あり

src/bank.ts

@@ -1,15 +1,21 @@
 import { Expression } from './expression';
 import { Currency, Money } from './money';
+import { Pair } from './pair';
 
 export class Bank {
+  private rates: { [key in string]: number } = {}
+
   reduce(source: Expression, to: Currency):Money {
     return source.reduce(this, to);
   }
 
-  addRate(from: string, to: string, rate: number) {
+  addRate(from: Currency, to: Currency, rate: number) {
+    const pair = new Pair(from, to);
+    this.rates[pair.key] = rate;
   }
 
   rate(from: Currency, to: Currency): number {
-    return from === 'CHF' && to === 'USD' ? 2 : 1
+    const pair = new Pair(from, to);
+    return this.rates[pair.key]
   }
 }

src/pair.ts

@@ -0,0 +1,18 @@
+import { Currency } from "./money";
+
+export class Pair{
+  constructor(private from: Currency, private to: Currency){
+  }
+
+  get key(): string {
+    return `${this.from}_${this.to}`;
+  }
+
+  equals(object: Object): boolean {
+    const pair = object as Pair;
+    if (!pair) 
+      return false;
+
+    return this.from === pair.from && this.to === pair.to;
+  }
+}