I see, so I had a different (and not valid) meaning of destructive
operations in mind!
Am 02.11.15 um 17:46 schrieb Waldek Hebisch:
> Johannes Grabmeier wrote:
>> but then there should be one consequence: one should remove all
>> destructive operations from lists, as they do not work. Then, this is
>> the bug, to lead to believe that one performs a destructive change. Or
>> at least: exclude the argument 1 for delete! and give an error.
> From ug01:
>
> : An operation that can be destructive on one or more arguments
> : usually has a name ending in a exclamation point (``!'').
> : This actually means that it is {\it allowed} to update its
> : arguments but it is not {\it required} to do so. For example,
> : the underlying representation of a collection type may not allow
> : the very last element to removed and so an empty object may be
> : returned instead. Therefore, it is important that you use the
> : object returned by the operation and not rely on a physical
> : change having occurred within the object. Usually, destructive
> : operations are provided for efficiency reasons.
>
> Docstring for 'delete!':
>
> delete!(u, i) destructively deletes the \spad{i}th element of u.
>
> "Working" means that operation is doing what is promised.
> AFAICS 'delete!' is keeping its promise: returned value
> is OK. I do not know what more could we do to make
> clear that 'delete!' is a version of 'delete' that may
> be used when you do not care what happens to the
> argument (for examples because you will forget the
> argument and only use returned value).
>
> Let me add that functions like 'delete!' (notably 'reverse!')
> are used in the algebra and give considerable efficiency gains.
>
>
--
Mit freundlichen Grüßen
Johannes Grabmeier
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