Index: generic/predefined.h
===================================================================
diff -u -r782f6b060b16282799fe936bc528f512e562362a -re45455a7ad52d4d849a0408243d175b4b4a52bb3
--- generic/predefined.h	(.../predefined.h)	(revision 782f6b060b16282799fe936bc528f512e562362a)
+++ generic/predefined.h	(.../predefined.h)	(revision e45455a7ad52d4d849a0408243d175b4b4a52bb3)
@@ -339,6 +339,7 @@
 "::xotcl::MetaSlot create ::xotcl::Attribute -superclass ::xotcl::ObjectParameterSlot\n"
 "createBootstrapAttributeSlots ::xotcl::Attribute {\n"
 "{value_check once}\n"
+"incremental\n"
 "initcmd\n"
 "valuecmd\n"
 "valuechangedcmd\n"
@@ -423,13 +424,30 @@
 "::xotcl2::Class create ::xotcl::Attribute::Optimizer {\n"
 ":method method args  {::xotcl::next; :optimize}\n"
 ":method forward args {::xotcl::next; :optimize}\n"
-":protected method init args    {::xotcl::next; :optimize}\n"
+":protected method init args {::xotcl::next; :optimize}\n"
 ":public method optimize {} {\n"
-"if {[set :multivalued]} return\n"
+"set object [expr {${:per-object} ? {object} : {}}]\n"
+"if {${:per-object}} {\n"
+"set perObject -per-object\n"
+"set infokind Object} else {\n"
+"set perObject \"\"\n"
+"set infokind Class}\n"
+"if {[::xotcl::cmd::${infokind}Info::method ${:domain} name ${:name}] ne \"\"} {\n"
+"::xotcl::forward ${:domain} {*}$perObject ${:name} \\\n"
+"${:manager} \\\n"
+"[list %1 [${:manager} defaultmethods]] %self \\\n"
+"${:methodname}}\n"
+"if {[info exists :incremental] && ${:incremental}} return\n"
 "if {[set :defaultmethods] ne {get assign}} return\n"
-"if {[:info callable -which assign] ne \"::xotcl::ObjectParameterSlot alias assign ::xotcl::setinstvar\"} return\n"
+"set assignInfo [:info callable -which assign]\n"
+"if {$assignInfo ne \"::xotcl::ObjectParameterSlot alias assign ::xotcl::setinstvar\" &&\n"
+"[lindex $assignInfo {end 0}] ne \"::xotcl::setinstvar\" } return\n"
 "if {[:info callable -which get]    ne \"::xotcl::ObjectParameterSlot alias get ::xotcl::setinstvar\"} return\n"
-"::xotcl::setter ${:domain} {*}[expr {${:per-object} ? \"-per-object\" : \"\"}] ${:name}}}\n"
+"array set \"\" [:toParameterSyntax ${:name}]\n"
+"if {$(mparam) ne \"\"} {\n"
+"set setterParam [lindex $(oparam) 0]} else {\n"
+"set setterParam ${:name}}\n"
+"::xotcl::setter ${:domain} {*}$perObject $setterParam}}\n"
 "::xotcl::Attribute mixin add ::xotcl::Attribute::Optimizer\n"
 "::xotcl2::Class public method parameter arglist {\n"
 "if {![::xotcl::is [::xotcl::self]::slot object]} {\n"
Index: generic/predefined.xotcl
===================================================================
diff -u -r782f6b060b16282799fe936bc528f512e562362a -re45455a7ad52d4d849a0408243d175b4b4a52bb3
--- generic/predefined.xotcl	(.../predefined.xotcl)	(revision 782f6b060b16282799fe936bc528f512e562362a)
+++ generic/predefined.xotcl	(.../predefined.xotcl)	(revision e45455a7ad52d4d849a0408243d175b4b4a52bb3)
@@ -654,6 +654,7 @@
   
   createBootstrapAttributeSlots ::xotcl::Attribute {
     {value_check once}
+    incremental
     initcmd
     valuecmd
     valuechangedcmd
@@ -779,6 +780,8 @@
       } else {
         #puts stderr "adding assign [list obj var value:$(mparam)] // for [self] with $(mparam)"
         :method assign [list obj var value:$(mparam),slot=[self]] {::xotcl::setinstvar $obj $var $value}
+        #::xotcl::setter ${:domain} ${:name}:$(mparam),slot=[self]
+        #puts stderr "::xotcl::setter ${:domain} ${:name}:$(mparam),slot=[self]"
       }
     }
     #append __initcmd [:mk_type_checker]
@@ -801,16 +804,43 @@
   ::xotcl2::Class create ::xotcl::Attribute::Optimizer {
     :method method args  {::xotcl::next; :optimize}
     :method forward args {::xotcl::next; :optimize}
-    :protected method init args    {::xotcl::next; :optimize}
+    :protected method init args {::xotcl::next; :optimize}
     :public method optimize {} {
-      #puts stderr OPTIMIZER
-      if {[set :multivalued]} return
+      #puts stderr OPTIMIZER-[info exists :incremental]
+      set object [expr {${:per-object} ? {object} : {}}]
+      if {${:per-object}} {
+        set perObject -per-object
+        set infokind Object
+      } else {
+        set perObject ""
+        set infokind Class
+      }
+      if {[::xotcl::cmd::${infokind}Info::method ${:domain} name ${:name}] ne ""} {
+        #puts stderr "RESETTING ${:domain} name ${:name}"
+        ::xotcl::forward ${:domain} {*}$perObject ${:name} \
+            ${:manager} \
+            [list %1 [${:manager} defaultmethods]] %self \
+            ${:methodname}
+      }
+      #if {[set :multivalued]} return
+      if {[info exists :incremental] && ${:incremental}} return
       if {[set :defaultmethods] ne {get assign}} return
-      #puts stderr assign=[:info callable -which assign]
-      if {[:info callable -which assign] ne "::xotcl::ObjectParameterSlot alias assign ::xotcl::setinstvar"} return
+      set assignInfo [:info callable -which assign]
+      #puts stderr assign=$assignInfo//[lindex $assignInfo {end 0}]
+      if {$assignInfo ne "::xotcl::ObjectParameterSlot alias assign ::xotcl::setinstvar" &&
+          [lindex $assignInfo {end 0}] ne "::xotcl::setinstvar" } return
       if {[:info callable -which get]    ne "::xotcl::ObjectParameterSlot alias get ::xotcl::setinstvar"} return
       #puts stderr "**** optimizing       [${:domain} info method definition ${:name}]"
-      ::xotcl::setter ${:domain} {*}[expr {${:per-object} ? "-per-object" : ""}] ${:name}
+
+      array set "" [:toParameterSyntax ${:name}]
+      if {$(mparam) ne ""} {
+        set setterParam [lindex $(oparam) 0]
+        #puts stderr "setterParam=$setterParam, op=$(oparam)"
+      } else {
+        set setterParam ${:name}
+      }
+      ::xotcl::setter ${:domain} {*}$perObject $setterParam
+      #puts stderr "::xotcl::setter ${:domain} {*}$perObject $setterParam"
     }
   }
   # register the optimizer per default
@@ -853,12 +883,14 @@
     }
     return $value
   }
+
   ::xotcl::Slot method type=baseclass {name value} {
     if {![::xotcl::is $value baseclass]} {
       error "expected baseclass but got \"$value\" for parameter $name"
     }
     return $value
   }
+
   ::xotcl::Slot method type=metaclass {name value} {
     if {![::xotcl::is $value metaclass]} {
       error "expected metaclass but got \"$value\" for parameter $name"
Index: tests/parameters.xotcl
===================================================================
diff -u -r496ffe8fb5e5bdaba56fe3a939d32634bdbcb088 -re45455a7ad52d4d849a0408243d175b4b4a52bb3
--- tests/parameters.xotcl	(.../parameters.xotcl)	(revision 496ffe8fb5e5bdaba56fe3a939d32634bdbcb088)
+++ tests/parameters.xotcl	(.../parameters.xotcl)	(revision e45455a7ad52d4d849a0408243d175b4b4a52bb3)
@@ -308,6 +308,11 @@
 ? {Foo create foo -ints {1 2}} "::foo"
 ? {Foo create foo -ints {1 a 2}} {invalid value in "1 a 2": expected integer but got "a" for parameter -ints}
 
+# make slot incremental
+Foo slot ints eval {
+  set :incremental 1
+  :optimize
+}
 Foo create foo -ints {1 2}
 ? {foo ints add 0} "0 1 2"
 ? {foo ints add a} {expected integer but got "a" for parameter value}
@@ -706,6 +711,10 @@
 ? {ParamTest create p -u c1} {expected upper but got "c1" for parameter -u}
 ? {ParamTest create p -us {A B c}} \
     {invalid value in "A B c": expected upper but got "c" for parameter -us}
+ParamTest slot us eval {
+  set :incremental 1
+  :optimize
+}
 ? {ParamTest create p -us {A B}} ::p
 ? {p us add C end} "A B C"
 
@@ -725,7 +734,7 @@
     "o" \
     "value is an object"
 ? {p o xxx} \
-    {expected object but got "xxx" for parameter value} \
+    {expected object but got "xxx" for parameter o} \
     "value is not an object"
 
 ParamTest slots {
@@ -740,7 +749,7 @@
     "value is a list of objects (multiple elements)"
 
 ? {p os {o xxx d1}} \
-    {invalid value in "o xxx d1": expected object but got "xxx" for parameter value} \
+    {invalid value in "o xxx d1": expected object but got "xxx" for parameter os} \
     "list with invalid object"
 
 #######################################################
@@ -825,7 +834,30 @@
 ? {::xotcl::setter o {d default}} {parameter "d" is not allowed to have default "default"}
 ? {::xotcl::setter o -x} {method name "-x" must not start with a dash}
 
+o destroy
 
+#######################################################
+# test for slot-optimizer
+#######################################################
+Test case slot-optimizer
+
+Class create C -parameter {a b:integer c:integer,multivalued}
+
+C create c1 
+? {c1 a 1} 1
+? {c1 b 1} 1
+? {c1 c 1} 1
+
+# before: 1st case: setter, 2&3: forward
+#slot-optimizer.001:	  1.50 mms, c1 a 1
+#slot-optimizer.002:	  3.30 mms, c1 b 1
+#slot-optimizer.003:	  3.40 mms, c1 c 1
+#
+# after: 1st, 2nd, 3rd case: setter 
+#slot-optimizer.001:	  1.50 mms, c1 a 1
+#slot-optimizer.002:	  1.50 mms, c1 b 1
+#slot-optimizer.003:	  1.60 mms, c1 c 1
+
 ## TODO regression test for type checking, parameter options (initcmd,
 ## substdefault, combinations with defaults, ...), etc.
 puts stderr =====END
Index: tests/slottest.xotcl
===================================================================
diff -u -rc942f4e117d2aa3c8594702e0476a3f73a4147df -re45455a7ad52d4d849a0408243d175b4b4a52bb3
--- tests/slottest.xotcl	(.../slottest.xotcl)	(revision c942f4e117d2aa3c8594702e0476a3f73a4147df)
+++ tests/slottest.xotcl	(.../slottest.xotcl)	(revision e45455a7ad52d4d849a0408243d175b4b4a52bb3)
@@ -342,7 +342,7 @@
 Class Person -slots {
   Attribute create name
   Attribute create age -default 0
-  Attribute create projects -default {} -multivalued true
+  Attribute create projects -default {} -multivalued true -incremental true
 }
 
 Person p1 -name "Gustaf"
@@ -386,7 +386,7 @@
 }
 
 Person slots {
-  Attribute create projects -default "" -multivalued true -type ::Project
+  Attribute create projects -default "" -multivalued true -incremental true -type ::Project
   Attribute create salary -type integer
 }