Immutable elements of FreeModuleTensor

[mkoeppe]

Currently, elements of a FiniteRankFreeModule and its tensor modules are mutable and therefore cannot be hashed.

In analogy to sage.modules.FreeModuleElement and sage.matrix.Matrix, a method set_immutable() should be added.

In this ticket, we do this by creating a subclass ModuleElementWithMutability of ModuleElement. The existing classes Vector (and thus FreeModuleElement from sage.modules) and FreeModuleTensor (from sage.tensor) are changed to subclass it.

The methods from FreeModuleElement implementing mutability are moved to ModuleElementWithMutability and become available for FreeModuleTensor in this way. (The class Vector also gets them for free.)

CC: @egourgoulhon @tscrim @mjungmath

Component: linear algebra

Author: Matthias Koeppe

Branch/Commit: a2ee8be

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/30181

[mkoeppe]

Author: Matthias Koeppe

[mkoeppe]

Description changed:

--- 
+++ 
@@ -2,4 +2,7 @@
 
 In analogy to `sage.modules.FreeModuleElement` and `sage.matrix.Matrix`, a method `set_immutable()` should be added.
 
+In this ticket, we do this by creating a subclass `ModuleElementWithMutability` of `ModuleElement`.  The existing classes `Vector` (and thus `FreeModuleElement` from `sage.modules`) and `FreeModuleTensor` (from `sage.tensor`) are changed to subclass it.
 
+The methods from `FreeModuleElement` implementing mutability are moved to `ModuleElementWithMutability` and become available for `FreeModuleTensor` in this way. (The class `Vector` also gets them for free.)
+

[mkoeppe]

Branch: u/mkoeppe/immutable_elements_of_freemoduletensor

[sagetrac-git]

Commit: 9df3d22

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

9df3d22

sage.tensor.modules: Make all zero() and one() elements immutable

[sagetrac-git]

Changed commit from 9df3d22 to 4373ea2

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

4373ea2

FreeModuleTensor: Replace special casing of the immutable zero by is_immutable

[mkoeppe]

comment:6

Although hashing is one of the motivations for this ticket, it will not be implemented on this ticket. A follow-up ticket will take care of it.

[tscrim]

comment:7

I would also make those methods

cpdef bool is_[im]mutable(self):

In some ways, I think this would be better as a mixin class. Alas, Cython does not have multiple inheritance...

[mkoeppe]

comment:8

There is already a mixin class written in Cython, sage.structure.mutability, but it cannot be used for exactly this reason.

[mkoeppe]

comment:9

Replying to @tscrim:

I would also make those methods

cpdef bool is_[im]mutable(self):

Yes, I'll make this change

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

a2ee8be

ModuleElementWithMutability.is_immutable, is_mutable: Change def to cpdef

[sagetrac-git]

Changed commit from 4373ea2 to a2ee8be

[tscrim]

comment:11

Thank you. LGTM.

(I slightly wonder if a user who really cares about speed should instead be just breaking the encapsulation here...)

[tscrim]

Reviewer: Travis Scrimshaw