document minimal AbstractCoefficients API

JuliaAlgebra · Apr 14, 2024 · c707b89 · c707b89
1 parent ece736f
commit c707b89
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Showing 2 changed files with 11 additions and 6 deletions.
diff --git a/src/coefficients.jl b/src/coefficients.jl
@@ -1,6 +1,15 @@
 """
     abstract type AbstractCoefficients{V,K} end
-Implements `Base.keys`, `Base.values`.
+Everything that implements a fixed set of methods can be used as
+`SparseCoefficients` without subtyping it.
+
+# "Read-only" coefficients
+E.g. returned by calls to a `MultiplicativeStructure` need to implement
+
+* `Base.keys`
+* `Base.values`
+* `StarAlgebras.canonical`
+* `StarAlgebras.star`
 """
 abstract type AbstractCoefficients{K,V} end
 

diff --git a/test/runtests.jl b/test/runtests.jl
@@ -8,15 +8,11 @@ import StarAlgebras as SA
 import MutableArithmetics as MA
 
 begin
-    # turning GroupsCore.GroupElement into SparseCoefficients
+    # turning GroupsCore.GroupElement into "read-only" SparseCoefficients
     import GroupsCore: GroupElement
-    Base.iszero(::GroupElement) = false
     Base.keys(g::GroupElement) = (g,)
     Base.values(::GroupElement) = (1,)
     SA.canonical(g::GroupElement) = g
-    function Base.getindex(g::GroupElement, h::GroupElement)
-        return ifelse(g == h, SA.aug(g), 0 * SA.aug(g))
-    end
     # missing above: Base.isless for the SA.canonical
     # TODO: implement sort by hashing for non-comparable elements?