Default == and isequal for NCRingElem

Author: fingolfin

src/NCRings.jl

@@ -83,15 +83,22 @@ end
 
 *(x::NCRingElement, y::NCRingElem) = parent(y)(x)*y
 
-function ==(x::NCRingElem, y::NCRingElem)
-   fl, u, v = try_promote(x, y)
-   if fl
-     return u == v
-   else
-     return false
-   end
- end
- 
+# == throws an error when inputs have different parent to help user
+# find bugs in their code
+function ==(a::NCRingElem, b::NCRingElem)
+  check_parent(a, b)
+  throw(NotImplementedError(:(==), x, y))
+end
+
+# isequal treats ring elements with differing parent as simply being not equal
+# (instead of throwing an exception like == does) as it is used to compare set
+# elements or keys in dictionaries, and there it seems at least plausible to
+# allow mixed parents
+function isequal(a::NCRingElem, b::NCRingElem)
+   return parent(a) == parent(b) && a == b
+end
+
+
 ==(x::NCRingElem, y::NCRingElement) = x == parent(x)(y)
 
 ==(x::NCRingElement, y::NCRingElem) = parent(y)(x) == y

src/Rings.jl

@@ -4,10 +4,6 @@
 #
 ###############################################################################
 
-function isequal(a::RingElem, b::RingElem)
-   return parent(a) == parent(b) && a == b
-end
-
 # Implement `isapprox` for ring elements via equality by default. On the one
 # hand, we need isapprox methods to be able to conformance test series rings.
 # On the other hand this is essentially the only sensible thing to do in