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Add Lint/UnusedSelf and Lint/UnusedPseudoMethod #543

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nobodywasishere opened this issue Jan 20, 2025 · 3 comments · May be fixed by #556
Open

Add Lint/UnusedSelf and Lint/UnusedPseudoMethod #543

nobodywasishere opened this issue Jan 20, 2025 · 3 comments · May be fixed by #556
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@nobodywasishere
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1.7.0

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@nobodywasishere
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nobodywasishere commented Jan 20, 2025 •
edited by Sija
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These cannot be redefined and do not have side effects:

  • self
  • pointerof
  • sizeof
  • instance_sizeof
  • alignof
  • instance_alignof
  • offsetof
  • typeof
  • is_a?
  • as
  • as?
  • responds_to?
  • nil?
  • !
class MyInt32
  def self.int_klass : Class
    if @var > 1
      self
    # ^^^^ error: Unused self
    end

    typeof(self)
    # ^^^^^^^^^^ error: Unused pseudo method

    !true
    # ^^^ error: Unused pseudo method
    
    Int32
  end
end
@straight-shoota
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Note: typeof does have a side effect. It forces the compiler to type its arguments, but without creating a code path where this could actually end up in codegen.

This mechanism is used quite a lot in stdlib specs for example. It ensures the respective code is semantically valid, without checking the execution result. For example: https://github.com/crystal-lang/crystal/blob/39aaae569f22e39a155dcfe5a962bd2660cc828f/spec/std/signal_spec.cr#L9-L11

@Sija Sija added the rule label Jan 21, 2025
@nobodywasishere
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I have these implemented. I'll create a PR once #537 is merged

@nobodywasishere
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as can also have a side effect of raising if the cast cannot be performed (this is used in a few places in the stdlib)

@nobodywasishere nobodywasishere linked a pull request Jan 29, 2025 that will close this issue
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@Sija Sija added this to the 1.7.0 milestone Jan 29, 2025
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Add Lint/UnusedSelf and Lint/UnusedPseudoMethod nobodywasishere/ameba
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@Sija @straight-shoota @nobodywasishere