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Idea: Preserve matchdata in rules #141

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avdi opened this issue Jun 15, 2016 · 5 comments · May be fixed by #372
Closed

Idea: Preserve matchdata in rules #141

avdi opened this issue Jun 15, 2016 · 5 comments · May be fixed by #372

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@avdi
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avdi commented Jun 15, 2016

Here's part of a rule I just wrote the other day:

stampfile_pattern = %r"^members/(?<email>.*)/\d{2}-(?<step>\w+).timestamp$"
rule stampfile_pattern do |t|
  match           = stampfile_pattern.match(t.name)
  email           = match[:email]
  step            = match[:step]
  # ...
end

Notice how, after it matches, I have to re-apply the regex inside the rule definition in order to pull out named matchdata.

I was thinking of introducing something like this as an alternative:

stampfile_pattern = %r"^members/(?<email>.*)/\d{2}-(?<step>\w+).timestamp$"
rule stampfile_pattern do |t|
  email           = t.matchdata[:email]
  step            = t.matchdata[:step]
  # ...
end

Before I dive in, what do you think? And is there another way to accomplish this that I've missed?
@drbrain
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drbrain commented Jun 16, 2016

I think this would be a nice addition.

I don't think there's a way to accomplish this without adding the feature to the rule.

I've not used a rule without dependencies, it gets triggered by a separate task that depends on the output (regexp)?

@avdi
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avdi commented Jun 16, 2016

I don't think there's a way to accomplish this without adding the feature to the rule.

Yeah, that's what I was thinking. I feel like it makes sense, since the task object already has the concrete t.name that matched, to also have the matchdata.

I've not used a rule without dependencies, it gets triggered by a separate task that depends on the output (regexp)?

Yep.

@avdi
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avdi commented Jun 16, 2016 •
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I've also thought about this:

rule %r"^members/(?<email>.*)/\d{2}-(?<step>\w+).timestamp$" => 
  "members/%{email}/some-input-file" do |t|
  email           = t.matchdata[:email]
  step            = t.matchdata[:step]
  # ...
end

I.e. adding the ability to substitute in backreferences in the rule source. Currently, rule sources suffer from the same problem as the rule body: if you want to reference regex matchdata, you have to use a lambda as the dependency and re-apply the regex.

@yeban
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yeban commented Dec 2, 2016

I stumbled upon this issue looking for how to access matchdata inside a rule. This would be a great addition, imho.

@avdi
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avdi commented Dec 2, 2016 via email

@fatkodima fatkodima mentioned this issue Dec 23, 2020
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@ruby ruby locked and limited conversation to collaborators Jun 21, 2022
@hsbt hsbt converted this issue into discussion #437 Jun 21, 2022

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Preserve match_data in rules fatkodima/rake
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@avdi @drbrain @yeban