lib: improve an AsList method for domains with ...

... stored GeneratorsOfDomain.

The new version ensures that no copy of GeneratorsOfDomain is created if
GeneratorsOfDomain already is a duplicate free list.

Adds tests for this situation.

lib/domain.gi

@@ -232,12 +232,18 @@ InstallImmediateMethod( Enumerator,
 InstallMethod( AsList,
     "for a domain with stored domain generators",
     [ IsDomain and HasGeneratorsOfDomain ],
-    D -> DuplicateFreeList( GeneratorsOfDomain( D ) ) );
+    function( D )
+        if IsDuplicateFreeList( GeneratorsOfDomain( D ) ) then
+            return GeneratorsOfDomain( D );
+        else
+            return DuplicateFreeList( GeneratorsOfDomain( D ) );
+        fi;
+    end );
 
 InstallMethod( Enumerator,
     "for a domain with stored domain generators",
     [ IsDomain and HasGeneratorsOfDomain ],
-    D -> DuplicateFreeList( GeneratorsOfDomain( D ) ) );
+    D -> AsList(D) );
 
 
 #############################################################################

tst/testinstall/domain.tst

@@ -21,5 +21,21 @@ false
 gap> M = J;
 Error, no method found for comparing two infinite domains
 
+# AsList and Enumerator for domains which know their GeneratorsOfDomain
+gap> r := Immutable([1..3]);;
+gap> d := Domain(r);;
+gap> IsIdenticalObj(AsList(d), r);
+true
+gap> IsIdenticalObj(Enumerator(d), r);
+true
+gap> r := Immutable([1,2,3,1]);;
+gap> d := Domain(r);;
+gap> IsIdenticalObj(GeneratorsOfDomain(d), r);
+true
+gap> IsIdenticalObj(AsList(d), r);
+false
+gap> IsIdenticalObj(Enumerator(d), r);
+false
+
 #
 gap> STOP_TEST("domain.tst");