#14711: Weak references in the coercion graph
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       Reporter:  jpflori            |        Owner:  davidloeffler
           Type:  defect             |       Status:  needs_review
       Priority:  critical           |    Milestone:  sage-5.13
      Component:  number fields      |   Resolution:
       Keywords:  memleak, number    |    Merged in:
  field, QuadraticField              |    Reviewers:
        Authors:  Simon King         |  Work issues:
Report Upstream:  N/A                |       Commit:
         Branch:                     |  364b9856b28d7060e3ea9825144de66c8f11ca2a
  u/SimonKing/ticket/14711           |     Stopgaps:
   Dependencies:                     |
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Comment (by SimonKing):

 Replying to [comment:129 SimonKing]:
 > Hence, I would argue that `C._coerce_map_from_(A)` returning a composite
 map is a misuse. Granted, it is far from obvious that it is a misuse. I
 feel tempted to investigate how often composite maps are actually returned
 by `_coerce_map_from_`.

 For example, I found that during startup of Sage composite maps are
 returned by `Q._coerce_map_from_(P)` for the following values of P, Q:
 {{{
 Coercion Rational Field to Complex Field with 2 bits of precision
 Coercion Rational Field to Complex Field with 53 bits of precision
 Coercion <type 'int'> to Univariate Polynomial Ring in x over Integer Ring
 Coercion Integer Ring to Complex Field with 2 bits of precision
 Coercion <type 'int'> to Complex Field with 53 bits of precision
 Coercion <type 'int'> to Real Interval Field with 53 bits of precision
 Coercion <type 'int'> to Univariate Polynomial Ring in x over Rational
 Field
 Coercion <type 'int'> to Real Interval Field with 64 bits of precision
 Coercion Complex Lazy Field to Complex Double Field
 Coercion <type 'int'> to Univariate Polynomial Ring in x over Algebraic
 Real Field
 }}}
 I guess in all of these cases the domain and the "middle parent" will be
 immortal anyway.

--
Ticket URL: <http://trac.sagemath.org/ticket/14711#comment:130>
Sage <http://www.sagemath.org>
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