Ruby Hash 雜湊表操作指南：建立、預設值、常用方法與鍵值存取

Hash 是鍵值對集合，鍵可為任意物件。本文說明建立方式、預設值機制、常用實例方法與巢狀結構應用。

建立 Hash

months = Hash.new                    # 空雜湊
months = Hash.new("month")           # 預設值 "month"
months = Hash["a" => 100, "b" => 200]  # 字面值
# 任意物件為鍵
[[1, "jan"]] => "January"

預設值行為

months = Hash.new("month")
months[0]   # "month"
months[72]  # "month"

常用實例方法

months = {"1" => "January", "2" => "February"}
keys = months.keys   # ["1", "2"]