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29 lines
1.3 KiB
Markdown
29 lines
1.3 KiB
Markdown
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# Notes on the mal implementation in Perl5.
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This implementation should work in any perl from 5.19.3 onwards.
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Earlier versions are likely to work too as long as you install a new
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List::Util. The implementation uses the experimental `switch`
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feature, which may make it vulnerable to future changes in perl.
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Mal objects are all in subclasses of `Mal::Type`, and can be treated
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as scalar, array, or hash references as appropriate.
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Metadata support uses `Hash::Util::FieldHash` to attach external
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metadata to objects. This means that in the metadata system imposes
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no overhead on the normal use of objects.
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Hash-maps are slightly magical. They're keyed by the stringified
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versions of mal objects, and `Mal::Scalar` overloads stringification
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so that this works properly.
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Tail-call optimisation uses Perl's built-in `goto &NAME` syntax for
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explicit tail calls. This allows functions defined by `fn*` to be
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implemented as functions at the Perl layer.
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Perl's garbage-collection is based on reference counting. This means
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that reference loops will cause memory leaks, and in particular using
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`def!` to define a function will cause that function to have a
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reference to the environment it's defined in, making a small reference
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loop and hence a memory leak. This can be avoided by carefully
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undefining any function before it goes out of scope.
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