`CSV::Row` pattern matching `Symbol` assumption
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描述
There's an assumption made in the pattern matching code which will make it very hard to use, and that's the presumption of Symbol keys on CSV::Row.
If you were to make a PM interface and look at the keys:
class Testing
def deconstruct_keys(keys)
p(keys:)
{}
end
end
# => :deconstruct_keys
Testing.new in a: 1, b: 2, c: 3
# {:keys=>[:a, :b, :c]}
# => false
You will receive Symbol keys. Why is this a problem? Because if you are loading CSV data it will most likely be from a file or String which we can take directly from the documentation:
# Headers are part of data
data = CSV.parse(<<~ROWS, headers: true)
Name,Department,Salary
Bob,Engineering,1000
Jane,Sales,2000
John,Management,5000
ROWS
data.class
#=> CSV::Table
data.first
#=> #<CSV::Row "Name":"Bob" "Department":"Engineering" "Salary":"1000">
If we were to test this against pattern matching (and adding a keys debugging statement):
data.select { _1 in Name: /^J/ }
{:keys=>[:Name]}
{:keys=>[:Name]}
{:keys=>[:Name]}
=> []
As it exists today this feature cannot be used except for manually created data like in the tests which will not be the experience of end users who either parse from a String or File.
I would like to propose that we modify the method to treat the keys as keyword arguments, rather than as Symbols, which will allow this feature to be used for common usecases:
class CSV::Row
def deconstruct_keys(keys)
if keys.nil?
to_h.transform_keys(&:to_sym)
else
keys.to_h do |key|
value = if self.key?(key)
self[key]
elsif self.key?(key.to_s)
self[key.to_s]
else
nil
end
[key, value]
end
end
end
end
This does, in a sense, conflate Symbol and String keys, but String keys are impossible in pattern matching:
CSV::Row.new(%w(A B), [1, 2], true) in "A" => 1
/Users/lemur/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/irb/workspace.rb:119:in `eval': (irb):14: syntax error, unexpected integer literal, expecting local variable or method (SyntaxError)
...A B), [1, 2], true) in "A" => 1
So the options are either have an interface which will only work with test data and users who manually create Symbol keys (which is a minority case), or consider a keyword-like approach that can handle the ambiguity of keys types.
I believe this is a reasonable assumption of coercion to make, as Ruby has done this in other cases with converting between Symbol and String whenever it is considered reasonable input from the user. I believe this would qualify as reasonable user input.
If this is of interest I can submit a PR, but wanted to run the idea by people first.
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调研方向
从 CSV::Row#deconstruct_keys 开始,检查针对手动创建行的现有模式匹配测试。使用 CSV.parse 和表头重现报告的案例,然后为解析后的 String 或 File 数据添加覆盖,并验证使用符号键的模式匹配能够正常工作且不会破坏现有的行行为。
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