dart, a nice way of replacing keys and values in maps? -

i have map , want go through both values , keys , replace occurrences of particular objects meet set criteria other objects, if find key meets specific criteria.
want swap key different object still points @ same value object in map, if find value want replace want original key point @ replacement value.
here code works simplified example looks quite ugly, there nicer way of achieving this, meaning method doesn't require extract every key , value want replace , write replacements in.
nicer able iterate of map once rather iterating on keys, , iterating on keys , values replaced?

void main(){   //replace values of instance object , keys starting "t" same key minus "t"   var m = {     "one": new a(),     "two": new a(),     "three": new b(),     "four": new b()   };   mapkeyandvalueswapper(m,     keymeetscondition: (k) => k.startswith("t"),     valuemeetscondition: (v) => v a,     keyreplacer: (k) => k.replacefirst("t", ""),     valuereplacer: (v) => new object());   print(m); }  mapkeyandvalueswapper(map m, {bool keymeetscondition(key), bool valuemeetscondition(value), dynamic keyreplacer(key), dynamic valuereplacer(value)}){   var keystoreplace = [];   var keystoreplacevaluesfor = [];   var keys = m.keys;   keys.foreach((k){     if(keymeetscondition != null){       if(keymeetscondition(k)){         keystoreplace.add(k);       }     }     if(valuemeetscondition != null){       if(valuemeetscondition(m[k])){         keystoreplacevaluesfor.add(k);       }     }   });   keystoreplacevaluesfor.foreach((k){     m[k] = valuereplacer(m[k]);   });   keystoreplace.foreach((k){     m[keyreplacer(k)] = m.remove(k);   }); }  class a{} class b{} 

i think same:

  map newmap = {};   m.foreach((k, v) {     var key = k;     var value = v;     if(m[k] a) {       value = new object();     }     if(k.startswith('t')) {       key = k.replacefirst('t', '');     }     newmap[key]=value;   });