Set factories

[nthiery]

At Sage days 30, a long brainstorm seems to have finalized the design. Here is a excerpt from the documentation:

A set factory F is device, whose goal is to construct parent P
which models subsets of a big set S. Typically, the P s are constructed
within families obtained by putting a bunch of constraints cons on the
elements of the set S. In such a hierarchy of subsets, one needs to have a
fine and easy control on the elements construction. That is, one often needs
that P constructs elements in a subclass of its usual class for element. On
the contrary, one also often needs P to be a facade parent, meaning that P
construct element whose actual parent is not P itself.

The role of a set factory is twofold:

• manage a database of constructors for the different parents P = F(cons)
  depending on the various kinds of constraints cons. Note: currently there
  is no real support for that. We are gathering use case before fixing the
  interface.

• ensure that the elements e = P(...) created by the different parents
  follows a consistent policy concerning their class and parent.

The patch implement this idea while trying to leave as much as possible space
for further improvement. In particular, I tried to specify the few possible
things about constraints. I'm even not completely sure about add_constraints.
Please comment and review.

Florent

CC: @sagetrac-sage-combinat @hivert

Component: combinatorics

Keywords: factories, days30, Cernay2012, days57

Author: Florent Hivert

Branch/Commit: 763f93c

Reviewer: Frédéric Chapoton

Issue created by migration from https://trac.sagemath.org/ticket/10194

[nthiery]

comment:1

Patch under development on the Sage-Combinat patch server.

[hivert]

Description changed:

--- 
+++ 
@@ -1 +1,3 @@
+At Sage days 30, a long brainstorm seems to have finalized the design. I'm writing a patch on sage combinat queue.
 
+  

[hivert]

Changed keywords from none to factories, days30

[hivert]

Changed keywords from factories, days30 to factories, days30, Cernay2012

[hivert]

Description changed:

--- 
+++ 
@@ -1,3 +1,29 @@
-At Sage days 30, a long brainstorm seems to have finalized the design. I'm writing a patch on sage combinat queue.
+At Sage days 30, a long brainstorm seems to have finalized the design. Here is a exerpt from the documentation:
 
-  
+A *set factory* `F` is device, whose goal is to construct parent `P`
+which models subsets of a big set `S`. Typically, the `P` s are constructed
+within families obtained by putting a bunch of constraints `cons` on the
+elements of the set `S`. In such a hierarchy of subsets, one needs to have a
+fine and easy control on the elements construction. That is, one often needs
+that `P` constructs elements in a subclass of its usual class for element. On
+the contrary, one also often needs `P` to be a facade parent, meaning that `P`
+construct element whose actual parent is not `P` itself.
+
+The role of a set factory is twofold:
+
+- *manage a database* of constructors for the different parents `P = F(cons)`
+  depending on the various kinds of constraints `cons`. Note: currently there
+  is no real support for that. We are gathering use case before fixing the
+  interface.
+
+- ensure that the elements `e = P(...)` created by the different parents
+  follows a consistent policy concerning their *class and parent*.
+
+The patch implement this idea while trying to leave as much as possible space 
+for further improvement. In particular, I tried to specify the few possible 
+things about constraints. I'm even not completely sure about `add_constraints`.
+Please comment and review.
+
+Florent
+
+**Apply :** [trac_10194-factories_policy-fh.patch](https://github.com/sagemath/sage-prod/files/10651310/trac_10194-factories_policy-fh.patch.gz)

[loefflerd]

Work Issues: doctest failures