feat: add residue ring/field maps

[thofma]

No description provided.

[thofma]

@lgoettgens Have you also encountered the following:

julia> using Revise, AbstractAlgebra

julia> R, f = residue_field(ZZ, 2)
(Residue field of integers modulo 2, Map: integers -> residue field)

julia> typeof(R)
AbstractAlgebra.Generic.EuclideanRingResidueField{BigInt}

julia> EuclideanRingResidueRing{BigInt} === AbstractAlgebra.Generic.EuclideanRingResidueRing{BigInt}
true

julia> EuclideanRingResidueRing{BigInt}
EuclideanRingResidueRing{BigInt}

julia> print(EuclideanRingResidueRing{BigInt})
EuclideanRingResidueRing{BigInt}

????

Is it correct, that I cannot make this type print nicely?

[lgoettgens]

I am not sure I understand the question. Is it about the AbstractAlgebra.Generic prefix only for one of the two types?

[lgoettgens]

I noticed that the following two lines are only in AbstractAlgebra.jl for EuclideanRingResidueRing and not *Field:

import .Generic: EuclideanRingResidueRing # line 658
export EuclideanRingResidueRing # line 865

and they are not there for things like MPoly or other AbstractAlgebra.Generic.* types.

Does this help for your question?

[lgoettgens]

Reacting to my comment above and your commit in-between: I would have rather removed the import/export shenanigans for EuclideanRingResidueRing instead of adding them for EuclideanRingResidueField as well, since for the other types in Generic. we don't export them as well (to keep the consistency).

Or do I remember correctly that you wanted to merge the abstract type and the concrete type for both of these? In this case I think one could argue that in this case they should no longer live inside of Generic. but outside and thus are allowed to be exported.

[thofma]

There is no corresponding AbstractAlgebra.EuclideanBla type, so there is no ambiguity when exporting them. Generic contains all concrete types, so I kept them there for now. I think there will eventually be no abstract type, but we can do this later.

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (a8efab2) 87.16% compared to head (91946be) 87.11%.
Report is 1 commits behind head on master.

Files	Patch %	Lines
src/generic/ResidueField.jl	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1559      +/-   ##
==========================================
- Coverage   87.16%   87.11%   -0.06%     
==========================================
  Files         115      114       -1     
  Lines       29412    29483      +71     
==========================================
+ Hits        25638    25685      +47     
- Misses       3774     3798      +24     

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