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allow == for two groups/group elements in fewer cases #4196

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merged 2 commits into from
Oct 15, 2024
Merged

allow == for two groups/group elements in fewer cases #4196

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7a20ddf
allow `==` for two groups/group elements in fewer cases
ThomasBreuer Oct 11, 2024
864daad
address a comment
ThomasBreuer Oct 11, 2024
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21 changes: 19 additions & 2 deletions src/Groups/GAPGroups.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -372,9 +372,26 @@ end

Base.:*(x::GAPGroupElem, y::GAPGroupElem) = _prod(x, y)

==(x::GAPGroup, y::GAPGroup) = GapObj(x) == GapObj(y)
function ==(x::GAPGroup, y::GAPGroup)
_check_compatible(x, y)
return GapObj(x) == GapObj(y)
end

# For two `BasicGAPGroupElem`s,
# we allow the question for equality if their parents fit together
# in the sense of `_check_compatible`,
# and compare the `GapObj`s if this is the case.
function ==(x::BasicGAPGroupElem, y::BasicGAPGroupElem)
_check_compatible(parent(x), parent(y))
return GapObj(x) == GapObj(y)
end

==(x::BasicGAPGroupElem, y::BasicGAPGroupElem ) = GapObj(x) == GapObj(y)
# For two `GAPGroupElem`s,
# if no specialized method is applicable then no `==` comparison is allowed.
function ==(x::GAPGroupElem, y::GAPGroupElem)
_check_compatible(parent(x), parent(y); error = false) || throw(ArgumentError("parents of x and y are not compatible"))
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Same here as above

throw(ArgumentError("== is not implemented for the given types"))
end
Comment on lines +389 to +394
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once Nemocas/AbstractAlgebra.jl#1853 is available, this method can be removed. maybe add this as a comment

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My point of view is:
If the compatibility check returns false then we are sure that the question for == is not allowed,
but if the compatibility check returns true then likely there is a new subtype of GAPGroupElem for which a == method should be provided.
(Currently we have just the subtypes BasicGAPGroupElem and MatrixGroupElem.)


"""
one(G::GAPGroup) -> elem_type(G)
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4 changes: 4 additions & 0 deletions test/Groups/conformance.jl
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Expand Up @@ -60,6 +60,10 @@ include(joinpath(dirname(pathof(AbstractAlgebra)), "..", "test", "Groups-conform
@test g>h || g==h || g<h
@test isequal(g,h) || isless(g,h) || isless(h,g)
end

F = free_group(1)
@test_throws ArgumentError F == G
@test_throws ArgumentError gen(F, 1) == g
end

@testset "Group operations" begin
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