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chromatic | 2 years ago

JSON::PP and Cpanel::JSON::XS don't have this problem somehow.

From my reading of the documentation of the former (especially the MAPPING section), it has the same problem for the same reasons.

the whole thing is a tangled mess of wrongness

Perl has monomorphic operators and polymorphic values. Every time someone tries to flip that, whether encoding arbitrary data structures to monomorphic values via a polymorphic visitor pattern, the smart-match experiment, or (as I already mentioned in this story's comments) polymorphic operators for data structure dereferencing, these problems occur.

Regardless of whether anyone believes that Perl's operator/value design is good or useful, that's how the language works. Working at cross purposes is an exercise in frustration. (I'll leave analogies about duck typing, contravariance, casting, and type erasure to people who like debating programming language design.)

discuss

order

WesolyKubeczek|2 years ago

Tests trump documentation, though:

      ~ perl -MJSON::XS -E 'my $d = {foo => 42}; say encode_json($d); $d->{foo} eq "bar"; say encode_json($d);'                                                                                                   
    {"foo":42}
    {"foo":"42"}
      ~ perl -MJSON::PP -E 'my $d = {foo => 42}; say encode_json($d); $d->{foo} eq "bar"; say encode_json($d);'
    {"foo":42}
    {"foo":42}
      ~ perl -MCpanel::JSON::XS -E 'my $d = {foo => 42}; say encode_json($d); $d->{foo} eq "bar"; say encode_json($d);'
    {"foo":42}
    {"foo":42}
So it seems either the documentation is now wrong, or the assumptions about "usage" are wrong except for JSON::Xs (on Perl 5.32.1).

However, it "works as documented" when the implicit conversion is the other way around:

      ~ perl -MCpanel::JSON::XS -E 'my $d = {foo => "42"}; say encode_json($d); $d->{foo} == 0; say encode_json($d);'
    {"foo":"42"}
    {"foo":42}
> Every time someone tries to flip that, whether encoding arbitrary data structures to monomorphic values via a polymorphic visitor pattern, the smart-match experiment, or (as I already mentioned in this story's comments) polymorphic operators for data structure dereferencing, these problems occur.

Nothing in the typelessness of the language, though, makes it necessary to flip any internal state of a variable, though, any time its usage context changes. Especially if the state is readable by public API. Even in a typeless language, the "primary" type of the thing, if it's queryable by anything at all, should intuitively be what it's being set to by assignment or other kind of explicit mutation.