Did D2 ever implement the Eiffel "old" construct? I do not see it
mentioned in "The D Programming Language", and the only reference I can
find in the newsgroup is a short discussion in June of 2007 that seemed
to go nowhere.
If not, has anyone developed a reasonable workaround? Thanks.
-- Davidson
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Brief description: in Eiffel,
old expr
can be used in post-conditions, and evaluates to the value of
expr
as of entry to the function. It's useful to help verify that the
function has done what it was supposed to, but especially powerful when
used in classes because it complements invariant: invariant tests what
has *not* varied (duh), old expr helps test what *has* varied to
ensure that it has varied *correctly*.
For example, the .Add() method of a Container class might in its
postcondition assert
assert( count == old count + 1 )
to ensure that *exactly* one element got added, no more and no less
