Hi
Sorry for replying to myself.
> In order to sanitize the behavior of objects, parents and elements in sage,
> I'm about to add some tests to the framework. I think they are all reasonable
> but I may be asking to much. Please comment about the following:
>
> 1 - Any SageObject must have an equality methods such that
> self == self and self != None
>
> 2 - Element construction should be idempotent. More precisely, for any
> element e within parent P, the equality P(e) == e must hold.
> This is for example needed by the constructor of many Parent with a base
> ring, such as matrices.
>
> 3 - .zero() and .one() must never be mutable. I'd like to enforce this by
> computing .__hash__(). Here I see two possibilities:
> * decide that for any monoid M, if M.one() implement __hash__ it must
> returns an int (not an Integer) and not raise an exception like in
> sage: m = matrix([1]).__hash__()
> ...
> TypeError: mutable matrices are unhashable
The following sentence is ambiguous:
> * decide that any element of a monoid must be hashable.
Please replace it by:
* decide that element of any monoid must have a __hash__ method,
which may raise an error for mutable element but never on .one()
(and .zero() in a commutative monoid).
> Do you think this is asking too much ?
>
> By the way, if you have ideas of other basic sanity checks which must be added
> please tell me.
Cheers,
Florent
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