in reply to Re: Mocking isa under Test::Deep
in thread Mocking isa under Test::Deep

The authors of a test tool have unilaterally decided that you [...] are [not] allowed to use a comparator function that they didn't provide,

A more accurate summary would be that a test tool uses a special class as a sentinel and complains if a sentinel value turns up in a place where it has no business being. Meanwhile, a sloppy hack to get around draconian type checking had the side effect of making a non-sentinel appear to be a sentinel. The solution was to make the hack slightly less sloppy.

I would put more blame on the type checking that requires the hack than on the use of an internal class name as a way to create and detect sentinels.

- tye        

  • Comment on Re^2: Mocking isa under Test::Deep (sentinel)

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Re^3: Mocking isa under Test::Deep (sentinel)
by BrowserUk (Patriarch) on May 03, 2016 at 04:26 UTC
    A more accurate summary would be ...

    I'll take your word on that. I just looked through it all again and I can see that my original conclusion was less than the full story.

    That said, the breaking change is to Test::Deeply; appears (to me) to be digging into the guts of perl (via Scalar::Util::blessed()) to prevent their users from using fairly ordinary OO techniques to bypass their checks; and breaking stuff that worked for their users, all for the sake of the unjustified* and nebulous goal of 'improvement' of their own code base.

    That's akin to Stanley embossing a weak point on the shafts of their screwdrivers to prevent users from using them as levers.

    (*As in, not explained anywhere I could find.)

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[reply]
      appears (to me) to be digging into the guts of perl (via Scalar::Util::blessed()) to prevent their users from using fairly ordinary OO techniques to bypass their checks

      Actually not. You could remove the use of Scalar::Util::blessed() and the code would function identically. Test::Deep is using isa() to enable users to extend the Test::Deep::Cmp functionality using ordinary OO techniques.

      If they had actually used blessed() in a way that prevents such extending then the "breaking change" would have been avoided. Replace the new code: 

      if (! $Expects and Scalar::Util::blessed($d1) and $d1->isa("Test::Deep
+::Cmp"))

      [download]

      with code that looks too closely under the covers: 

      if (! $Expects and Scalar::Util::blessed($d1) eq "Test::Deep::Cmp")

      [download]

      and the fact that isa() was intentionally broken in order to do a sloppy hack to subvert draconian type checking would not have mattered.

      - tye        

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