Mostly because perlapi is not a thoroughly and well designed API but just a subset of the Perl internals exposed, including functions, structures and macros.

That means that whenever the representation of any structure used by perl internally changes, all the code must be recompiled and as you can imagine, evolving the language requires changing its internals...

In reply to Re: Rationale for why successive Perl releases are not XS-compatible? by salva
in thread Rationale for why successive Perl releases are not XS-compatible? by vrk

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