|Subject:||Re: [Liberty-eiffel] renaming of ARRAY comparison features|
|Date:||Wed, 15 Jun 2016 23:03:13 +0200|
PaoloThanks to everyoneCyril, I quite don't remember the rationale behind this change. As it is as you wrote quite big, may you please sketch out the rationale of it?May I ask you to give us a little test that triggers this bug? So we may add it to our test suiteThank you for this bug report.Beside the semantic change it should not have crashed your code.
This change has been made with commit 08f1f3646e833f254070b9b4432e27876dcc7cd0 (see https://github.com/LibertyEiffel/Liberty/commit/08f1f3646e833f254070b9b4432e27876dcc7cd0 for details) and it was labelled that way:
"BIG SEMANTIC SHIFT: is_equal now uses the is_equal of its elements (old is_equal_map). The old behaviour (using basic = comparison) is available through fast_is_equal."2016-06-14 19:30 GMT+02:00 Laurie Moye <address@hidden>:I have recently got an old SmallEiffel/SmartEifel program to compile
with Liberty. It runs, but immediately crashes with a segmentation fault.
Investigation shows that this is due to a stack overflow caused by
infinite recursion of ARRAY.is_equal.
ARRAY has always had two comparison features. One compares every item in
the arrays with '='. I shall refer to this as the "safe" one as it is
incapable of causing recursion. The other compares the items in the
arrays with "is_equal". I shall refer to this as the "treacherous" one
as it can lead to recursion.
In SmallEiffel and SmartEiffel, the safe comparison feature was called
"is_equal". This conforms to the description of "is_equal" in both ETL
The treacherous version was called "is_equal_map" in SmallEiffel and
In Liberty Eiffel, the name "is_equal" has been taken and given to the
treacherous version. The safe version has been renamed "fast_is_equal".
This is the reason my program crashed. When all occurrences of
"is_equal" are changed to "fast_is_equal" it runs happily.
Neiher SmallEiffel nor SmartEiffel seem to have ever used is_equal_map.
I have never found a use for it. Libery Eiffel does not seem to use
I cannot see why the names would have been changed. Giving the name
"is_equal" to the treacherous version goes againt what I have always
thought the purpose of is_equal to be; namely a shallow comparison
feature in which any objects contained within the objects being tested
are required to be the same set of objects. I have never seen the point
of the treacherous version, If an array contains complex objects which
one wants to compare with something deeper than '=', it is most likely
that the precise details of the comparison will be depend upon the new
class being defined. An inhereted test itself using is_equal is unlikely
to meet any specific requirement, and is a dangerous thing to have
around. This point is made in the wiki:
in connection with a TRIANGLE class:
"It is very hard to imagine how a good function for comparison could be
defined automatically. In particular, it is not always enough to call
is_equal again on the attribute".
I assume that there was a very good reason for changing the names, but I
can't find any documentation of it. Is there an explanation of it?
Does the compiler now need to use the treacherous version?
Is giving the name "is_equal" to the treacherous version the right thing
to have done?
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