ruby 中带哈希的字符串插值

Question

我的目标是用散列值替换字符串中的键。我是这样做的：

"hello %{name}, today is %{day}" % {name: "Tim", day: "Monday"}

如果字符串中的键在哈希中丢失：

"hello %{name}, today is %{day}" % {name: "Tim", city: "Lahore"}

然后它会抛出一个错误。

KeyError: key{day} not found

预期结果应为：

"hello Tim, today is %{day}" or "hello Tim, today is "

有人可以指导我只替换匹配的键而不抛出任何错误吗？

Answer 1

从 Ruby 2.3 开始，% 遵循通过 default= 设置的默认值：

hash = {name: 'Tim', city: 'Lahore'}
hash.default = ''

'hello %{name}, today is %{day}' % hash
#=> "hello Tim, today is "

或通过 default_proc= 设置的动态默认值：

hash = {name: 'Tim', city: 'Lahore'}
hash.default_proc = proc { |h, k| "%{#{k}}" }

'hello %{name}, today is %{day}' % hash
#=> "hello Tim, today is %{day}"

请注意，只有缺少的密钥，即 :day 会传递给 proc。因此，它不知道您是否在格式字符串中使用 %{day} 或 %<day>s，这可能会导致不同的输出：

'hello %{name}, today is %<day>s' % hash
#=> "hello Tim, today is %{day}"

Answer 2

您可以设置默认哈希值：

h = {name: "Tim", city: "Lahore"}
h.default = "No key"
p "hello %{name}, today is %{day}" % h #=>"hello Tim, today is No key"

Answer 3

我有带空格的哈希键，在将键转换为符号后它起作用了。

带字符串键的哈希（它在插值时返回错误）：

hash = {"First Name" => "Allama", "Last Name" => "Iqbal"}

将散列键转换为符号对我有用：

hash = {:"First Name" => "Allama", :"Last Name" => "Iqbal"}
hash.default = ''

'The %{First Name} %{Last Name} was a great poet.' % hash

// The Allama Iqbal was a great poet.

ruby 中带哈希的字符串插值

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