String interpolation ?

[fcbry]

Hi,
In bash if I want to interpolate a variable into a string I can do (contrived example):

$V=" hello "
echo "I say${V},you say goodbye."
I say hello, you say goodbye.

Now, I want to do a fix, this works fine (Elixir):

rule:
  any:
    - pattern: |
        defmodule $M do 
          IO.puts($A)
        end
fix: |
  defmodule $M do 
    def msg($A) do 
      IO.puts(:stdout,$A)
    end 
  end

But say, I want to rename the Elixir module (suffix it with "ConcreteFactoryImpl")(lets pretend we're Java devs:

Now $M wont match. I could append a quoted string but that wouldn't produce a valid module name.

Ideally, unless I'm being silly, variables could be expressed in a ${M} form so that they could be expressed in strings, like so:

rule:
  any:
    - pattern: |
        defmodule $M do 
          IO.puts($A)
        end
fix: |
  defmodule ${M}ConcreteFactoryImpl do 
    def msg($A) do 
      IO.puts(:stdout,$A)
    end 
  end

Is there a better way to do this?

[fcbry]

I seem to have gotten around this by splicing in $_ (which evaluates to nothing in this case) to separate the variable $M and the text that follows.

rule:
  any:
    - pattern: |
        defmodule $M do 
          IO.puts($A)
        end
fix: |
  defmodule $M$_ConcreteFactoryImpl do 
    def msg($A) do 
      IO.puts(:stdout,$A)
    end 
  end

Woops, wrong, it's still eating the letter 'C'

[HerringtonDarkholme]

This can be done via transform operation.
The trick here is $NEW_MOD can be freely changed via regex replacement.

rule:
  any:
    - pattern: |
        defmodule $M do 
          IO.puts($A)
        end
transform:
  NEW_MOD:
    replace:
      by: ConcreteFactoryImpl
      replace: $
      source: $M
fix: |
  defmodule $NEW_MOD do 
    def msg($A) do 
      IO.puts(:stdout,$A)
    end 
  end

https://ast-grep.github.io/playground.html#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

[HerringtonDarkholme]

[fcbry]

Nice!