review confident ruby

再读confident ruby(performing work部分)

再读confident ruby，记下以下要点。

每个函数应包含4部分

1. collecting input
2. performing work
3. delivering result
4. handling failures

performing work的模式

这个部分只有一个pattern

sending a strong message

要发消息给trused object,需要3个条件

1. 识别要完成工作所需要发送的消息
2. 识别这些消息对应的roles
3. 确保method能担任这些roles

一个从文件中读取用户信息，并发邮件的例子

需要做以下步骤

1. Parse the purchase records from the CSV contained in a provided IO object.
2. For each purchase record, use the record’s email address to get the associated customer record, or, if the email hasn’t been seen before, create a new customer record in our system.
3. Use the legacy record’s product ID to find or create a product record in our system.
4. Add the product to the customer record’s list of purchases.
5. Notify the customer of the new location where they can download their files and update their account info.
6. Log the successful import of the purchase record.

识别message

1. #parse_legacy_purchase_records.
2. For #each purchase record, use the record’s #email_address to #get_customer.
3. Use the record’s #product_id to #get_product.
4. #add_purchased_product to the customer record.
5. #notify_of_files_available for the purchased product.
6. #log_successful_import of the product record.

识别roles

关于duck type

不要在method中再根据type写分支逻辑，而是首先找出我们需要什么样的message和role，然后确保我们在程序里只允许使用准备好的duck