diff --git a/compiler/ast.nim b/compiler/ast.nim
index a3f17a0627..431740543a 100644
--- a/compiler/ast.nim
+++ b/compiler/ast.nim
@@ -780,10 +780,6 @@ proc hash*(x: ItemId): Hash =
 
 
 type
-  TIdObj* {.acyclic.} = object of RootObj
-    itemId*: ItemId
-  PIdObj* = ref TIdObj
-
   PNode* = ref TNode
   TNodeSeq* = seq[PNode]
   PType* = ref TType
@@ -886,7 +882,8 @@ type
   PScope* = ref TScope
 
   PLib* = ref TLib
-  TSym* {.acyclic.} = object of TIdObj # Keep in sync with PackedSym
+  TSym* {.acyclic.} = object # Keep in sync with PackedSym
+    itemId*: ItemId
     # proc and type instantiations are cached in the generic symbol
     case kind*: TSymKind
     of routineKinds:
@@ -955,11 +952,12 @@ type
     attachedTrace,
     attachedDeepCopy
 
-  TType* {.acyclic.} = object of TIdObj # \
+  TType* {.acyclic.} = object # \
                               # types are identical iff they have the
                               # same id; there may be multiple copies of a type
                               # in memory!
                               # Keep in sync with PackedType
+    itemId*: ItemId
     kind*: TTypeKind          # kind of type
     callConv*: TCallingConvention # for procs
     flags*: TTypeFlags        # flags of the type
@@ -991,24 +989,6 @@ type
 
   TPairSeq* = seq[TPair]
 
-  TIdPair* = object
-    key*: PIdObj
-    val*: RootRef
-
-  TIdPairSeq* = seq[TIdPair]
-  TIdTable* = object # the same as table[PIdent] of PObject
-    counter*: int
-    data*: TIdPairSeq
-
-  TIdNodePair* = object
-    key*: PIdObj
-    val*: PNode
-
-  TIdNodePairSeq* = seq[TIdNodePair]
-  TIdNodeTable* = object # the same as table[PIdObj] of PNode
-    counter*: int
-    data*: TIdNodePairSeq
-
   TNodePair* = object
     h*: Hash                 # because it is expensive to compute!
     key*: PNode
@@ -1146,7 +1126,7 @@ proc getPIdent*(a: PNode): PIdent {.inline.} =
 const
   moduleShift = when defined(cpu32): 20 else: 24
 
-template id*(a: PIdObj): int =
+template id*(a: PType | PSym): int =
   let x = a
   (x.itemId.module.int shl moduleShift) + x.itemId.item.int
 
@@ -1445,11 +1425,6 @@ proc copyStrTable*(dest: var TStrTable, src: TStrTable) =
   setLen(dest.data, src.data.len)
   for i in 0..high(src.data): dest.data[i] = src.data[i]
 
-proc copyIdTable*(dest: var TIdTable, src: TIdTable) =
-  dest.counter = src.counter
-  newSeq(dest.data, src.data.len)
-  for i in 0..high(src.data): dest.data[i] = src.data[i]
-
 proc copyObjectSet*(dest: var TObjectSet, src: TObjectSet) =
   dest.counter = src.counter
   setLen(dest.data, src.data.len)
@@ -1770,24 +1745,10 @@ proc initStrTable*(): TStrTable =
   result = TStrTable(counter: 0)
   newSeq(result.data, StartSize)
 
-proc initIdTable*(): TIdTable =
-  result = TIdTable(counter: 0)
-  newSeq(result.data, StartSize)
-
-proc resetIdTable*(x: var TIdTable) =
-  x.counter = 0
-  # clear and set to old initial size:
-  setLen(x.data, 0)
-  setLen(x.data, StartSize)
-
 proc initObjectSet*(): TObjectSet =
   result = TObjectSet(counter: 0)
   newSeq(result.data, StartSize)
 
-proc initIdNodeTable*(): TIdNodeTable =
-  result = TIdNodeTable(counter: 0)
-  newSeq(result.data, StartSize)
-
 proc initNodeTable*(): TNodeTable =
   result = TNodeTable(counter: 0)
   newSeq(result.data, StartSize)
@@ -2308,3 +2269,16 @@ const
 proc isTrue*(n: PNode): bool =
   n.kind == nkSym and n.sym.kind == skEnumField and n.sym.position != 0 or
     n.kind == nkIntLit and n.intVal != 0
+
+type
+  TypeMapping* = Table[ItemId, PType]
+  SymMapping* = Table[ItemId, PSym]
+
+template idTableGet*(tab: typed; key: PSym | PType): untyped = tab.getOrDefault(key.itemId)
+template idTablePut*(tab: typed; key, val: PSym | PType) = tab[key.itemId] = val
+
+template initSymMapping*(): Table[ItemId, PSym] = initTable[ItemId, PSym]()
+template initTypeMapping*(): Table[ItemId, PType] = initTable[ItemId, PType]()
+
+template resetIdTable*(tab: Table[ItemId, PSym]) = tab.clear()
+template resetIdTable*(tab: Table[ItemId, PType]) = tab.clear()
diff --git a/compiler/astalgo.nim b/compiler/astalgo.nim
index 0fd13de00c..851a82e605 100644
--- a/compiler/astalgo.nim
+++ b/compiler/astalgo.nim
@@ -65,16 +65,6 @@ template mdbg*: bool {.deprecated.} =
   else:
     error()
 
-# --------------------------- ident tables ----------------------------------
-proc idTableGet*(t: TIdTable, key: PIdObj): RootRef
-proc idTableGet*(t: TIdTable, key: int): RootRef
-proc idTablePut*(t: var TIdTable, key: PIdObj, val: RootRef)
-proc idTableHasObjectAsKey*(t: TIdTable, key: PIdObj): bool
-  # checks if `t` contains the `key` (compared by the pointer value, not only
-  # `key`'s id)
-proc idNodeTableGet*(t: TIdNodeTable, key: PIdObj): PNode
-proc idNodeTablePut*(t: var TIdNodeTable, key: PIdObj, val: PNode)
-
 # ---------------------------------------------------------------------------
 
 proc lookupInRecord*(n: PNode, field: PIdent): PSym
@@ -723,119 +713,6 @@ iterator items*(tab: TStrTable): PSym =
     yield s
     s = nextIter(it, tab)
 
-proc hasEmptySlot(data: TIdPairSeq): bool =
-  for h in 0..high(data):
-    if data[h].key == nil:
-      return true
-  result = false
-
-proc idTableRawGet(t: TIdTable, key: int): int =
-  var h: Hash
-  h = key and high(t.data)    # start with real hash value
-  while t.data[h].key != nil:
-    if t.data[h].key.id == key:
-      return h
-    h = nextTry(h, high(t.data))
-  result = - 1
-
-proc idTableHasObjectAsKey(t: TIdTable, key: PIdObj): bool =
-  var index = idTableRawGet(t, key.id)
-  if index >= 0: result = t.data[index].key == key
-  else: result = false
-
-proc idTableGet(t: TIdTable, key: PIdObj): RootRef =
-  var index = idTableRawGet(t, key.id)
-  if index >= 0: result = t.data[index].val
-  else: result = nil
-
-proc idTableGet(t: TIdTable, key: int): RootRef =
-  var index = idTableRawGet(t, key)
-  if index >= 0: result = t.data[index].val
-  else: result = nil
-
-iterator pairs*(t: TIdTable): tuple[key: int, value: RootRef] =
-  for i in 0..high(t.data):
-    if t.data[i].key != nil:
-      yield (t.data[i].key.id, t.data[i].val)
-
-proc idTableRawInsert(data: var TIdPairSeq, key: PIdObj, val: RootRef) =
-  var h: Hash
-  h = key.id and high(data)
-  while data[h].key != nil:
-    assert(data[h].key.id != key.id)
-    h = nextTry(h, high(data))
-  assert(data[h].key == nil)
-  data[h].key = key
-  data[h].val = val
-
-proc idTablePut(t: var TIdTable, key: PIdObj, val: RootRef) =
-  var
-    index: int
-    n: TIdPairSeq
-  index = idTableRawGet(t, key.id)
-  if index >= 0:
-    assert(t.data[index].key != nil)
-    t.data[index].val = val
-  else:
-    if mustRehash(t.data.len, t.counter):
-      newSeq(n, t.data.len * GrowthFactor)
-      for i in 0..high(t.data):
-        if t.data[i].key != nil:
-          idTableRawInsert(n, t.data[i].key, t.data[i].val)
-      assert(hasEmptySlot(n))
-      swap(t.data, n)
-    idTableRawInsert(t.data, key, val)
-    inc(t.counter)
-
-iterator idTablePairs*(t: TIdTable): tuple[key: PIdObj, val: RootRef] =
-  for i in 0..high(t.data):
-    if not isNil(t.data[i].key): yield (t.data[i].key, t.data[i].val)
-
-proc idNodeTableRawGet(t: TIdNodeTable, key: PIdObj): int =
-  var h: Hash
-  h = key.id and high(t.data) # start with real hash value
-  while t.data[h].key != nil:
-    if t.data[h].key.id == key.id:
-      return h
-    h = nextTry(h, high(t.data))
-  result = - 1
-
-proc idNodeTableGet(t: TIdNodeTable, key: PIdObj): PNode =
-  var index: int
-  index = idNodeTableRawGet(t, key)
-  if index >= 0: result = t.data[index].val
-  else: result = nil
-
-proc idNodeTableRawInsert(data: var TIdNodePairSeq, key: PIdObj, val: PNode) =
-  var h: Hash
-  h = key.id and high(data)
-  while data[h].key != nil:
-    assert(data[h].key.id != key.id)
-    h = nextTry(h, high(data))
-  assert(data[h].key == nil)
-  data[h].key = key
-  data[h].val = val
-
-proc idNodeTablePut(t: var TIdNodeTable, key: PIdObj, val: PNode) =
-  var index = idNodeTableRawGet(t, key)
-  if index >= 0:
-    assert(t.data[index].key != nil)
-    t.data[index].val = val
-  else:
-    if mustRehash(t.data.len, t.counter):
-      var n: TIdNodePairSeq
-      newSeq(n, t.data.len * GrowthFactor)
-      for i in 0..high(t.data):
-        if t.data[i].key != nil:
-          idNodeTableRawInsert(n, t.data[i].key, t.data[i].val)
-      swap(t.data, n)
-    idNodeTableRawInsert(t.data, key, val)
-    inc(t.counter)
-
-iterator pairs*(t: TIdNodeTable): tuple[key: PIdObj, val: PNode] =
-  for i in 0..high(t.data):
-    if not isNil(t.data[i].key): yield (t.data[i].key, t.data[i].val)
-
 proc initIITable(x: var TIITable) =
   x.counter = 0
   newSeq(x.data, StartSize)
diff --git a/compiler/concepts.nim b/compiler/concepts.nim
index e44b0d1cd4..220c7e1419 100644
--- a/compiler/concepts.nim
+++ b/compiler/concepts.nim
@@ -309,7 +309,7 @@ proc conceptMatchNode(c: PContext; n: PNode; m: var MatchCon): bool =
     # error was reported earlier.
     result = false
 
-proc conceptMatch*(c: PContext; concpt, arg: PType; bindings: var TIdTable; invocation: PType): bool =
+proc conceptMatch*(c: PContext; concpt, arg: PType; bindings: var TypeMapping; invocation: PType): bool =
   ## Entry point from sigmatch. 'concpt' is the concept we try to match (here still a PType but
   ## we extract its AST via 'concpt.n.lastSon'). 'arg' is the type that might fullfill the
   ## concept's requirements. If so, we return true and fill the 'bindings' with pairs of
diff --git a/compiler/evaltempl.nim b/compiler/evaltempl.nim
index 98c6f4b829..bd0875213f 100644
--- a/compiler/evaltempl.nim
+++ b/compiler/evaltempl.nim
@@ -17,8 +17,8 @@ type
     owner, genSymOwner: PSym
     instLines: bool   # use the instantiation lines numbers
     isDeclarative: bool
-    mapping: TIdTable # every gensym'ed symbol needs to be mapped to some
-                      # new symbol
+    mapping: SymMapping # every gensym'ed symbol needs to be mapped to some
+                        # new symbol
     config: ConfigRef
     ic: IdentCache
     instID: int
@@ -47,7 +47,7 @@ proc evalTemplateAux(templ, actual: PNode, c: var TemplCtx, result: PNode) =
         handleParam actual[s.owner.typ.signatureLen + s.position - 1]
       else:
         internalAssert c.config, sfGenSym in s.flags or s.kind == skType
-        var x = PSym(idTableGet(c.mapping, s))
+        var x = idTableGet(c.mapping, s)
         if x == nil:
           x = copySym(s, c.idgen)
           # sem'check needs to set the owner properly later, see bug #9476
@@ -186,7 +186,7 @@ proc evalTemplate*(n: PNode, tmpl, genSymOwner: PSym;
     genSymOwner: genSymOwner,
     config: conf,
     ic: ic,
-    mapping: initIdTable(),
+    mapping: initSymMapping(),
     instID: instID[],
     idgen: idgen
   )
diff --git a/compiler/sem.nim b/compiler/sem.nim
index 1ae7d46264..92c21aecef 100644
--- a/compiler/sem.nim
+++ b/compiler/sem.nim
@@ -530,7 +530,7 @@ proc semAfterMacroCall(c: PContext, call, macroResult: PNode,
         # e.g. template foo(T: typedesc): seq[T]
         # We will instantiate the return type here, because
         # we now know the supplied arguments
-        var paramTypes = initIdTable()
+        var paramTypes = initTypeMapping()
         for param, value in genericParamsInMacroCall(s, call):
           var givenType = value.typ
           # the sym nodes used for the supplied generic arguments for
diff --git a/compiler/semcall.nim b/compiler/semcall.nim
index 447a672084..c3a2e77a71 100644
--- a/compiler/semcall.nim
+++ b/compiler/semcall.nim
@@ -663,7 +663,7 @@ proc inheritBindings(c: PContext, x: var TCandidate, expectedType: PType) =
         if t[i] == nil or u[i] == nil: return
         stackPut(t[i], u[i])
     of tyGenericParam:
-      let prebound = x.bindings.idTableGet(t).PType
+      let prebound = x.bindings.idTableGet(t)
       if prebound != nil:
         continue # Skip param, already bound
 
diff --git a/compiler/semdata.nim b/compiler/semdata.nim
index f3d661ff1f..12930fecad 100644
--- a/compiler/semdata.nim
+++ b/compiler/semdata.nim
@@ -41,7 +41,7 @@ type
     breakInLoop*: bool        # whether we are in a loop without block
     next*: PProcCon           # used for stacking procedure contexts
     mappingExists*: bool
-    mapping*: TIdTable
+    mapping*: Table[ItemId, PSym]
     caseContext*: seq[tuple[n: PNode, idx: int]]
     localBindStmts*: seq[PNode]
 
@@ -122,8 +122,6 @@ type
     converters*: seq[PSym]
     patterns*: seq[PSym]       # sequence of pattern matchers
     optionStack*: seq[POptionEntry]
-    symMapping*: TIdTable      # every gensym'ed symbol needs to be mapped
-                               # to some new symbol in a generic instantiation
     libs*: seq[PLib]           # all libs used by this module
     semConstExpr*: proc (c: PContext, n: PNode; expectedType: PType = nil): PNode {.nimcall.} # for the pragmas
     semExpr*: proc (c: PContext, n: PNode, flags: TExprFlags = {}, expectedType: PType = nil): PNode {.nimcall.}
@@ -138,8 +136,8 @@ type
     semOverloadedCall*: proc (c: PContext, n, nOrig: PNode,
                               filter: TSymKinds, flags: TExprFlags, expectedType: PType = nil): PNode {.nimcall.}
     semTypeNode*: proc(c: PContext, n: PNode, prev: PType): PType {.nimcall.}
-    semInferredLambda*: proc(c: PContext, pt: TIdTable, n: PNode): PNode
-    semGenerateInstance*: proc (c: PContext, fn: PSym, pt: TIdTable,
+    semInferredLambda*: proc(c: PContext, pt: Table[ItemId, PType], n: PNode): PNode
+    semGenerateInstance*: proc (c: PContext, fn: PSym, pt: Table[ItemId, PType],
                                 info: TLineInfo): PSym
     includedFiles*: IntSet    # used to detect recursive include files
     pureEnumFields*: TStrTable   # pure enum fields that can be used unambiguously
@@ -251,14 +249,14 @@ proc popProcCon*(c: PContext) {.inline.} = c.p = c.p.next
 
 proc put*(p: PProcCon; key, val: PSym) =
   if not p.mappingExists:
-    p.mapping = initIdTable()
+    p.mapping = initTable[ItemId, PSym]()
     p.mappingExists = true
   #echo "put into table ", key.info
-  p.mapping.idTablePut(key, val)
+  p.mapping[key.itemId] = val
 
 proc get*(p: PProcCon; key: PSym): PSym =
   if not p.mappingExists: return nil
-  result = PSym(p.mapping.idTableGet(key))
+  result = p.mapping.getOrDefault(key.itemId)
 
 proc getGenSym*(c: PContext; s: PSym): PSym =
   if sfGenSym notin s.flags: return s
diff --git a/compiler/semexprs.nim b/compiler/semexprs.nim
index d39ec6b717..4d0d436628 100644
--- a/compiler/semexprs.nim
+++ b/compiler/semexprs.nim
@@ -2418,7 +2418,7 @@ proc instantiateCreateFlowVarCall(c: PContext; t: PType;
   let sym = magicsys.getCompilerProc(c.graph, "nimCreateFlowVar")
   if sym == nil:
     localError(c.config, info, "system needs: nimCreateFlowVar")
-  var bindings: TIdTable = initIdTable()
+  var bindings = initTypeMapping()
   bindings.idTablePut(sym.ast[genericParamsPos][0].typ, t)
   result = c.semGenerateInstance(c, sym, bindings, info)
   # since it's an instantiation, we unmark it as a compilerproc. Otherwise
diff --git a/compiler/seminst.nim b/compiler/seminst.nim
index cfbc678e78..e9b46c382e 100644
--- a/compiler/seminst.nim
+++ b/compiler/seminst.nim
@@ -34,7 +34,7 @@ proc pushProcCon*(c: PContext; owner: PSym) =
 const
   errCannotInstantiateX = "cannot instantiate: '$1'"
 
-iterator instantiateGenericParamList(c: PContext, n: PNode, pt: TIdTable): PSym =
+iterator instantiateGenericParamList(c: PContext, n: PNode, pt: TypeMapping): PSym =
   internalAssert c.config, n.kind == nkGenericParams
   for a in n.items:
     internalAssert c.config, a.kind == nkSym
@@ -43,7 +43,7 @@ iterator instantiateGenericParamList(c: PContext, n: PNode, pt: TIdTable): PSym
       let symKind = if q.typ.kind == tyStatic: skConst else: skType
       var s = newSym(symKind, q.name, c.idgen, getCurrOwner(c), q.info)
       s.flags.incl {sfUsed, sfFromGeneric}
-      var t = PType(idTableGet(pt, q.typ))
+      var t = idTableGet(pt, q.typ)
       if t == nil:
         if tfRetType in q.typ.flags:
           # keep the generic type and allow the return type to be bound
@@ -92,7 +92,7 @@ when false:
   proc `$`(x: PSym): string =
     result = x.name.s & " " & " id " & $x.id
 
-proc freshGenSyms(c: PContext; n: PNode, owner, orig: PSym, symMap: var TIdTable) =
+proc freshGenSyms(c: PContext; n: PNode, owner, orig: PSym, symMap: var SymMapping) =
   # we need to create a fresh set of gensym'ed symbols:
   #if n.kind == nkSym and sfGenSym in n.sym.flags:
   #  if n.sym.owner != orig:
@@ -100,7 +100,7 @@ proc freshGenSyms(c: PContext; n: PNode, owner, orig: PSym, symMap: var TIdTable
   if n.kind == nkSym and sfGenSym in n.sym.flags: # and
     #  (n.sym.owner == orig or n.sym.owner.kind in {skPackage}):
     let s = n.sym
-    var x = PSym(idTableGet(symMap, s))
+    var x = idTableGet(symMap, s)
     if x != nil:
       n.sym = x
     elif s.owner == nil or s.owner.kind == skPackage:
@@ -124,7 +124,7 @@ proc instantiateBody(c: PContext, n, params: PNode, result, orig: PSym) =
     inc c.inGenericInst
     # add it here, so that recursive generic procs are possible:
     var b = n[bodyPos]
-    var symMap: TIdTable = initIdTable()
+    var symMap = initSymMapping()
     if params != nil:
       for i in 1..<params.len:
         let param = params[i].sym
@@ -174,12 +174,12 @@ proc instGenericContainer(c: PContext, info: TLineInfo, header: PType,
                           allowMetaTypes = false): PType =
   internalAssert c.config, header.kind == tyGenericInvocation
 
-  var cl: TReplTypeVars = TReplTypeVars(symMap: initIdTable(),
-        localCache: initIdTable(), typeMap: LayeredIdTable(),
+  var cl: TReplTypeVars = TReplTypeVars(symMap: initSymMapping(),
+        localCache: initTypeMapping(), typeMap: LayeredIdTable(),
         info: info, c: c, allowMetaTypes: allowMetaTypes
       )
 
-  cl.typeMap.topLayer = initIdTable()
+  cl.typeMap.topLayer = initTypeMapping()
 
   # We must add all generic params in scope, because the generic body
   # may include tyFromExpr nodes depending on these generic params.
@@ -217,7 +217,7 @@ proc referencesAnotherParam(n: PNode, p: PSym): bool =
       if referencesAnotherParam(n[i], p): return true
     return false
 
-proc instantiateProcType(c: PContext, pt: TIdTable,
+proc instantiateProcType(c: PContext, pt: TypeMapping,
                          prc: PSym, info: TLineInfo) =
   # XXX: Instantiates a generic proc signature, while at the same
   # time adding the instantiated proc params into the current scope.
@@ -332,7 +332,7 @@ proc getLocalPassC(c: PContext, s: PSym): string =
     for p in n:
       extractPassc(p)
 
-proc generateInstance(c: PContext, fn: PSym, pt: TIdTable,
+proc generateInstance(c: PContext, fn: PSym, pt: TypeMapping,
                       info: TLineInfo): PSym =
   ## Generates a new instance of a generic procedure.
   ## The `pt` parameter is a type-unsafe mapping table used to link generic
diff --git a/compiler/semstmts.nim b/compiler/semstmts.nim
index 677edbec60..028f06f893 100644
--- a/compiler/semstmts.nim
+++ b/compiler/semstmts.nim
@@ -1834,7 +1834,7 @@ proc semProcAnnotation(c: PContext, prc: PNode;
 
       return result
 
-proc semInferredLambda(c: PContext, pt: TIdTable, n: PNode): PNode =
+proc semInferredLambda(c: PContext, pt: TypeMapping, n: PNode): PNode =
   ## used for resolving 'auto' in lambdas based on their callsite
   var n = n
   let original = n[namePos].sym
diff --git a/compiler/semtypinst.nim b/compiler/semtypinst.nim
index d1327a3aee..f0ce8d76f0 100644
--- a/compiler/semtypinst.nim
+++ b/compiler/semtypinst.nim
@@ -9,6 +9,8 @@
 
 # This module does the instantiation of generic types.
 
+import std / tables
+
 import ast, astalgo, msgs, types, magicsys, semdata, renderer, options,
   lineinfos, modulegraphs
 
@@ -64,14 +66,14 @@ proc cacheTypeInst(c: PContext; inst: PType) =
 
 type
   LayeredIdTable* {.acyclic.} = ref object
-    topLayer*: TIdTable
+    topLayer*: TypeMapping
     nextLayer*: LayeredIdTable
 
   TReplTypeVars* = object
     c*: PContext
     typeMap*: LayeredIdTable  # map PType to PType
-    symMap*: TIdTable         # map PSym to PSym
-    localCache*: TIdTable     # local cache for remembering already replaced
+    symMap*: SymMapping         # map PSym to PSym
+    localCache*: TypeMapping     # local cache for remembering already replaced
                               # types during instantiation of meta types
                               # (they are not stored in the global cache)
     info*: TLineInfo
@@ -86,23 +88,23 @@ proc replaceTypeVarsTAux(cl: var TReplTypeVars, t: PType): PType
 proc replaceTypeVarsS(cl: var TReplTypeVars, s: PSym, t: PType): PSym
 proc replaceTypeVarsN*(cl: var TReplTypeVars, n: PNode; start=0; expectedType: PType = nil): PNode
 
-proc initLayeredTypeMap*(pt: TIdTable): LayeredIdTable =
+proc initLayeredTypeMap*(pt: sink TypeMapping): LayeredIdTable =
   result = LayeredIdTable()
-  copyIdTable(result.topLayer, pt)
+  result.topLayer = pt
 
 proc newTypeMapLayer*(cl: var TReplTypeVars): LayeredIdTable =
-  result = LayeredIdTable(nextLayer: cl.typeMap, topLayer: initIdTable())
+  result = LayeredIdTable(nextLayer: cl.typeMap, topLayer: initTable[ItemId, PType]())
 
 proc lookup(typeMap: LayeredIdTable, key: PType): PType =
   result = nil
   var tm = typeMap
   while tm != nil:
-    result = PType(idTableGet(tm.topLayer, key))
+    result = getOrDefault(tm.topLayer, key.itemId)
     if result != nil: return
     tm = tm.nextLayer
 
 template put(typeMap: LayeredIdTable, key, value: PType) =
-  idTablePut(typeMap.topLayer, key, value)
+  typeMap.topLayer[key.itemId] = value
 
 template checkMetaInvariants(cl: TReplTypeVars, t: PType) = # noop code
   when false:
@@ -361,7 +363,7 @@ proc handleGenericInvocation(cl: var TReplTypeVars, t: PType): PType =
   var header = t
   # search for some instantiation here:
   if cl.allowMetaTypes:
-    result = PType(idTableGet(cl.localCache, t))
+    result = getOrDefault(cl.localCache, t.itemId)
   else:
     result = searchInstTypes(cl.c.graph, t)
 
@@ -400,7 +402,7 @@ proc handleGenericInvocation(cl: var TReplTypeVars, t: PType): PType =
   if not cl.allowMetaTypes:
     cacheTypeInst(cl.c, result)
   else:
-    idTablePut(cl.localCache, t, result)
+    cl.localCache[t.itemId] = result
 
   let oldSkipTypedesc = cl.skipTypedesc
   cl.skipTypedesc = true
@@ -547,7 +549,7 @@ proc replaceTypeVarsTAux(cl: var TReplTypeVars, t: PType): PType =
         # type
         #   Vector[N: static[int]] = array[N, float64]
         #   TwoVectors[Na, Nb: static[int]] = (Vector[Na], Vector[Nb])
-        result = PType(idTableGet(cl.localCache, t))
+        result = getOrDefault(cl.localCache, t.itemId)
         if result != nil: return result
       inc cl.recursionLimit
 
@@ -623,7 +625,7 @@ proc replaceTypeVarsTAux(cl: var TReplTypeVars, t: PType): PType =
   of tyGenericInst, tyUserTypeClassInst:
     bailout()
     result = instCopyType(cl, t)
-    idTablePut(cl.localCache, t, result)
+    cl.localCache[t.itemId] = result
     for i in FirstGenericParamAt..<result.kidsLen:
       result[i] = replaceTypeVarsT(cl, result[i])
     propagateToOwner(result, result.last)
@@ -635,7 +637,7 @@ proc replaceTypeVarsTAux(cl: var TReplTypeVars, t: PType): PType =
       result = instCopyType(cl, t)
       result.size = -1 # needs to be recomputed
       #if not cl.allowMetaTypes:
-      idTablePut(cl.localCache, t, result)
+      cl.localCache[t.itemId] = result
 
       for i, resulti in result.ikids:
         if resulti != nil:
@@ -690,11 +692,11 @@ proc replaceTypeVarsTAux(cl: var TReplTypeVars, t: PType): PType =
 
 proc initTypeVars*(p: PContext, typeMap: LayeredIdTable, info: TLineInfo;
                    owner: PSym): TReplTypeVars =
-  result = TReplTypeVars(symMap: initIdTable(),
-            localCache: initIdTable(), typeMap: typeMap,
+  result = TReplTypeVars(symMap: initSymMapping(),
+            localCache: initTypeMapping(), typeMap: typeMap,
             info: info, c: p, owner: owner)
 
-proc replaceTypesInBody*(p: PContext, pt: TIdTable, n: PNode;
+proc replaceTypesInBody*(p: PContext, pt: TypeMapping, n: PNode;
                          owner: PSym, allowMetaTypes = false,
                          fromStaticExpr = false, expectedType: PType = nil): PNode =
   var typeMap = initLayeredTypeMap(pt)
@@ -731,7 +733,7 @@ proc recomputeFieldPositions*(t: PType; obj: PNode; currPosition: var int) =
     inc currPosition
   else: discard "cannot happen"
 
-proc generateTypeInstance*(p: PContext, pt: TIdTable, info: TLineInfo,
+proc generateTypeInstance*(p: PContext, pt: TypeMapping, info: TLineInfo,
                            t: PType): PType =
   # Given `t` like Foo[T]
   # pt: Table with type mappings: T -> int
@@ -747,7 +749,7 @@ proc generateTypeInstance*(p: PContext, pt: TIdTable, info: TLineInfo,
     var position = 0
     recomputeFieldPositions(objType, objType.n, position)
 
-proc prepareMetatypeForSigmatch*(p: PContext, pt: TIdTable, info: TLineInfo,
+proc prepareMetatypeForSigmatch*(p: PContext, pt: TypeMapping, info: TLineInfo,
                                  t: PType): PType =
   var typeMap = initLayeredTypeMap(pt)
   var cl = initTypeVars(p, typeMap, info, nil)
@@ -756,6 +758,6 @@ proc prepareMetatypeForSigmatch*(p: PContext, pt: TIdTable, info: TLineInfo,
   result = replaceTypeVarsT(cl, t)
   popInfoContext(p.config)
 
-template generateTypeInstance*(p: PContext, pt: TIdTable, arg: PNode,
+template generateTypeInstance*(p: PContext, pt: TypeMapping, arg: PNode,
                                t: PType): untyped =
   generateTypeInstance(p, pt, arg.info, t)
diff --git a/compiler/sigmatch.nim b/compiler/sigmatch.nim
index e831a28562..30ce24500d 100644
--- a/compiler/sigmatch.nim
+++ b/compiler/sigmatch.nim
@@ -15,7 +15,7 @@ import
   magicsys, idents, lexer, options, parampatterns, trees,
   linter, lineinfos, lowerings, modulegraphs, concepts
 
-import std/[intsets, strutils]
+import std/[intsets, strutils, tables]
 
 when defined(nimPreviewSlimSystem):
   import std/assertions
@@ -55,7 +55,7 @@ type
     calleeScope*: int        # scope depth:
                              # is this a top-level symbol or a nested proc?
     call*: PNode             # modified call
-    bindings*: TIdTable      # maps types to types
+    bindings*: TypeMapping   # maps types to types
     magic*: TMagic           # magic of operation
     baseTypeMatch: bool      # needed for conversions from T to openarray[T]
                              # for example
@@ -113,14 +113,14 @@ proc initCandidateAux(ctx: PContext,
 proc initCandidate*(ctx: PContext, callee: PType): TCandidate =
   result = initCandidateAux(ctx, callee)
   result.calleeSym = nil
-  result.bindings = initIdTable()
+  result.bindings = initTypeMapping()
 
 proc put(c: var TCandidate, key, val: PType) {.inline.} =
   ## Given: proc foo[T](x: T); foo(4)
   ## key: 'T'
   ## val: 'int' (typeof(4))
   when false:
-    let old = PType(idTableGet(c.bindings, key))
+    let old = idTableGet(c.bindings, key)
     if old != nil:
       echo "Putting ", typeToString(key), " ", typeToString(val), " and old is ", typeToString(old)
       if typeToString(old) == "float32":
@@ -141,7 +141,7 @@ proc initCandidate*(ctx: PContext, callee: PSym,
   result.diagnostics = @[] # if diagnosticsEnabled: @[] else: nil
   result.diagnosticsEnabled = diagnosticsEnabled
   result.magic = result.calleeSym.magic
-  result.bindings = initIdTable()
+  result.bindings = initTypeMapping()
   if binding != nil and callee.kind in routineKinds:
     var typeParams = callee.ast[genericParamsPos]
     for i in 1..min(typeParams.len, binding.len-1):
@@ -174,7 +174,7 @@ proc copyCandidate(dest: var TCandidate, src: TCandidate) =
   dest.calleeSym = src.calleeSym
   dest.call = copyTree(src.call)
   dest.baseTypeMatch = src.baseTypeMatch
-  copyIdTable(dest.bindings, src.bindings)
+  dest.bindings = src.bindings
 
 proc typeRel*(c: var TCandidate, f, aOrig: PType,
               flags: TTypeRelFlags = {}): TTypeRelation
@@ -362,7 +362,7 @@ proc concreteType(c: TCandidate, t: PType; f: PType = nil): PType =
   of tyGenericParam, tyAnything, tyConcept:
     result = t
     while true:
-      result = PType(idTableGet(c.bindings, t))
+      result = idTableGet(c.bindings, t)
       if result == nil:
         break # it's ok, no match
         # example code that triggers it:
@@ -500,7 +500,7 @@ proc genericParamPut(c: var TCandidate; last, fGenericOrigin: PType) =
   if fGenericOrigin != nil and last.kind == tyGenericInst and
      last.kidsLen-1 == fGenericOrigin.kidsLen:
     for i in FirstGenericParamAt..<fGenericOrigin.kidsLen:
-      let x = PType(idTableGet(c.bindings, fGenericOrigin[i]))
+      let x = idTableGet(c.bindings, fGenericOrigin[i])
       if x == nil:
         put(c, fGenericOrigin[i], last[i])
 
@@ -639,7 +639,7 @@ proc procParamTypeRel(c: var TCandidate; f, a: PType): TTypeRelation =
     a = a
 
   if a.isMetaType:
-    let aResolved = PType(idTableGet(c.bindings, a))
+    let aResolved = idTableGet(c.bindings, a)
     if aResolved != nil:
       a = aResolved
   if a.isMetaType:
@@ -763,7 +763,7 @@ proc matchUserTypeClass*(m: var TCandidate; ff, a: PType): PType =
         typeParamName = ff.base[i-1].sym.name
         typ = ff[i]
         param: PSym = nil
-        alreadyBound = PType(idTableGet(m.bindings, typ))
+        alreadyBound = idTableGet(m.bindings, typ)
 
       if alreadyBound != nil: typ = alreadyBound
 
@@ -1090,7 +1090,7 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
 
       case f.kind
       of tyGenericParam:
-        var prev = PType(idTableGet(c.bindings, f))
+        var prev = idTableGet(c.bindings, f)
         if prev != nil: candidate = prev
       of tyFromExpr:
         let computedType = tryResolvingStaticExpr(c, f.n).typ
@@ -1140,7 +1140,7 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
     return res
 
   template considerPreviousT(body: untyped) =
-    var prev = PType(idTableGet(c.bindings, f))
+    var prev = idTableGet(c.bindings, f)
     if prev == nil: body
     else: return typeRel(c, prev, a, flags)
 
@@ -1265,7 +1265,7 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
       var fRange = f.indexType
       var aRange = a.indexType
       if fRange.kind in {tyGenericParam, tyAnything}:
-        var prev = PType(idTableGet(c.bindings, fRange))
+        var prev = idTableGet(c.bindings, fRange)
         if prev == nil:
           put(c, fRange, a.indexType)
           fRange = a
@@ -1502,7 +1502,7 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
     else:
       result = isNone
   of tyGenericInst:
-    var prev = PType(idTableGet(c.bindings, f))
+    var prev = idTableGet(c.bindings, f)
     let origF = f
     var f = if prev == nil: f else: prev
 
@@ -1634,14 +1634,14 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
         #
         # we steal the generic parameters from the tyGenericBody:
         for i in 1..<f.len:
-          let x = PType(idTableGet(c.bindings, genericBody[i-1]))
+          let x = idTableGet(c.bindings, genericBody[i-1])
           if x == nil:
             discard "maybe fine (for e.g. a==tyNil)"
           elif x.kind in {tyGenericInvocation, tyGenericParam}:
             internalError(c.c.graph.config, "wrong instantiated type!")
           else:
             let key = f[i]
-            let old = PType(idTableGet(c.bindings, key))
+            let old = idTableGet(c.bindings, key)
             if old == nil:
               put(c, key, x)
             elif typeRel(c, old, x, flags + {trDontBind}) == isNone:
@@ -1764,7 +1764,7 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
         result = isGeneric
   of tyGenericParam:
     let doBindGP = doBind or trBindGenericParam in flags
-    var x = PType(idTableGet(c.bindings, f))
+    var x = idTableGet(c.bindings, f)
     if x == nil:
       if c.callee.kind == tyGenericBody and not c.typedescMatched:
         # XXX: The fact that generic types currently use tyGenericParam for
@@ -1828,7 +1828,7 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
         elif doBind:
           # careful: `trDontDont` (set by `checkGeneric`) is not always respected in this call graph.
           # typRel having two different modes (binding and non-binding) can make things harder to
-          # reason about and maintain. Refactoring typeRel to not be responsible for setting, or 
+          # reason about and maintain. Refactoring typeRel to not be responsible for setting, or
           # at least validating, bindings can have multiple benefits. This is debatable. I'm not 100% sure.
           # A design that allows a proper complexity analysis of types like `tyOr` would be ideal.
           concrete = concreteType(c, a, f)
@@ -1846,7 +1846,7 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
       result = typeRel(c, x, a, flags) # check if it fits
       if result > isGeneric: result = isGeneric
   of tyStatic:
-    let prev = PType(idTableGet(c.bindings, f))
+    let prev = idTableGet(c.bindings, f)
     if prev == nil:
       if aOrig.kind == tyStatic:
         if f.base.kind notin {tyNone, tyGenericParam}:
@@ -1899,7 +1899,7 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
         c.inferredTypes.add f
         f.add a
   of tyTypeDesc:
-    var prev = PType(idTableGet(c.bindings, f))
+    var prev = idTableGet(c.bindings, f)
     if prev == nil:
       # proc foo(T: typedesc, x: T)
       # when `f` is an unresolved typedesc, `a` could be any
@@ -1983,7 +1983,7 @@ proc cmpTypes*(c: PContext, f, a: PType): TTypeRelation =
 
 proc getInstantiatedType(c: PContext, arg: PNode, m: TCandidate,
                          f: PType): PType =
-  result = PType(idTableGet(m.bindings, f))
+  result = idTableGet(m.bindings, f)
   if result == nil:
     result = generateTypeInstance(c, m.bindings, arg, f)
   if result == nil:
@@ -2200,9 +2200,9 @@ proc paramTypesMatchAux(m: var TCandidate, f, a: PType,
     var instantiationCounter = 0
     var lastBindingCount = -1
     while r in {isBothMetaConvertible, isInferred, isInferredConvertible} and
-        lastBindingCount != m.bindings.counter and
+        lastBindingCount != m.bindings.len and
         instantiationCounter < 100:
-      lastBindingCount = m.bindings.counter
+      lastBindingCount = m.bindings.len
       inc(instantiationCounter)
       if arg.kind in {nkProcDef, nkFuncDef, nkIteratorDef} + nkLambdaKinds:
         result = c.semInferredLambda(c, m.bindings, arg)
@@ -2359,10 +2359,10 @@ proc paramTypesMatch*(m: var TCandidate, f, a: PType,
   else:
     # symbol kinds that don't participate in symchoice type disambiguation:
     let matchSet = {low(TSymKind)..high(TSymKind)} - {skModule, skPackage, skType}
-    
+
     var best = -1
     result = arg
-    
+
     var actingF = f
     if f.kind == tyVarargs:
       if m.calleeSym.kind in {skTemplate, skMacro}:
@@ -2398,7 +2398,7 @@ proc paramTypesMatch*(m: var TCandidate, f, a: PType,
       x.calleeSym = m.calleeSym
       y.calleeSym = m.calleeSym
       z.calleeSym = m.calleeSym
-      
+
       for i in 0..<arg.len:
         if arg[i].sym.kind in matchSet:
           copyCandidate(z, m)
@@ -2783,7 +2783,7 @@ proc matches*(c: PContext, n, nOrig: PNode, m: var TCandidate) =
         # proc foo(x: T = 0.0)
         # foo()
         if {tfImplicitTypeParam, tfGenericTypeParam} * formal.typ.flags != {}:
-          let existing = PType(idTableGet(m.bindings, formal.typ))
+          let existing = idTableGet(m.bindings, formal.typ)
           if existing == nil or existing.kind == tyTypeDesc:
             # see bug #11600:
             put(m, formal.typ, defaultValue.typ)
diff --git a/compiler/suggest.nim b/compiler/suggest.nim
index 720418466e..21986b4d9a 100644
--- a/compiler/suggest.nim
+++ b/compiler/suggest.nim
@@ -38,7 +38,7 @@ from wordrecg import wDeprecated, wError, wAddr, wYield
 import std/[algorithm, sets, parseutils, tables]
 
 when defined(nimsuggest):
-  import std/tables, pathutils # importer
+  import pathutils # importer
 
 const
   sep = '\t'
diff --git a/compiler/transf.nim b/compiler/transf.nim
index a92527fd1e..ab5e9f6250 100644
--- a/compiler/transf.nim
+++ b/compiler/transf.nim
@@ -18,6 +18,8 @@
 # * performs lambda lifting for closure support
 # * transforms 'defer' into a 'try finally' statement
 
+import std / tables
+
 import
   options, ast, astalgo, trees, msgs,
   idents, renderer, types, semfold, magicsys, cgmeth,
@@ -38,7 +40,7 @@ import closureiters, lambdalifting
 
 type
   PTransCon = ref object # part of TContext; stackable
-    mapping: TIdNodeTable     # mapping from symbols to nodes
+    mapping: Table[ItemId, PNode]     # mapping from symbols to nodes
     owner: PSym               # current owner
     forStmt: PNode            # current for stmt
     forLoopBody: PNode   # transformed for loop body
@@ -76,7 +78,7 @@ proc newTransNode(kind: TNodeKind, n: PNode,
 
 proc newTransCon(owner: PSym): PTransCon =
   assert owner != nil
-  result = PTransCon(mapping: initIdNodeTable(), owner: owner)
+  result = PTransCon(mapping: initTable[ItemId, PNode](), owner: owner)
 
 proc pushTransCon(c: PTransf, t: PTransCon) =
   t.next = c.transCon
@@ -159,7 +161,7 @@ proc transformSymAux(c: PTransf, n: PNode): PNode =
   else:
     b = n
   while tc != nil:
-    result = idNodeTableGet(tc.mapping, b.sym)
+    result = getOrDefault(tc.mapping, b.sym.itemId)
     if result != nil:
       # this slightly convoluted way ensures the line info stays correct:
       if result.kind == nkSym:
@@ -194,7 +196,7 @@ proc transformVarSection(c: PTransf, v: PNode): PNode =
       if vn.kind == nkSym:
         internalAssert(c.graph.config, it.len == 3)
         let x = freshVar(c, vn.sym)
-        idNodeTablePut(c.transCon.mapping, vn.sym, x)
+        c.transCon.mapping[vn.sym.itemId] = x
         var defs = newTransNode(nkIdentDefs, it.info, 3)
         if importantComments(c.graph.config):
           # keep documentation information:
@@ -215,7 +217,7 @@ proc transformVarSection(c: PTransf, v: PNode): PNode =
       for j in 0..<it.len-2:
         if it[j].kind == nkSym:
           let x = freshVar(c, it[j].sym)
-          idNodeTablePut(c.transCon.mapping, it[j].sym, x)
+          c.transCon.mapping[it[j].sym.itemId] = x
           defs[j] = x
         else:
           defs[j] = transform(c, it[j])
@@ -256,7 +258,7 @@ proc transformBlock(c: PTransf, n: PNode): PNode =
   var labl: PSym
   if c.inlining > 0:
     labl = newLabel(c, n[0])
-    idNodeTablePut(c.transCon.mapping, n[0].sym, newSymNode(labl))
+    c.transCon.mapping[n[0].sym.itemId] = newSymNode(labl)
   else:
     labl =
       if n[0].kind != nkEmpty:
@@ -328,7 +330,7 @@ proc introduceNewLocalVars(c: PTransf, n: PNode): PNode =
   of nkProcDef: # todo optimize nosideeffects?
     result = newTransNode(n)
     let x = newSymNode(copySym(n[namePos].sym, c.idgen))
-    idNodeTablePut(c.transCon.mapping, n[namePos].sym, x)
+    c.transCon.mapping[n[namePos].sym.itemId] = x
     result[namePos] = x # we have to copy proc definitions for iters
     for i in 1..<n.len:
       result[i] = introduceNewLocalVars(c, n[i])
@@ -759,7 +761,7 @@ proc transformFor(c: PTransf, n: PNode): PNode =
     let pa = putArgInto(arg, formal.typ)
     case pa
     of paDirectMapping:
-      idNodeTablePut(newC.mapping, formal, arg)
+      newC.mapping[formal.itemId] = arg
     of paFastAsgn, paFastAsgnTakeTypeFromArg:
       var t = formal.typ
       if pa == paFastAsgnTakeTypeFromArg:
@@ -773,10 +775,10 @@ proc transformFor(c: PTransf, n: PNode): PNode =
       #incl(temp.sym.flags, sfCursor)
       addVar(v, temp)
       stmtList.add(newAsgnStmt(c, nkFastAsgn, temp, arg, true))
-      idNodeTablePut(newC.mapping, formal, temp)
+      newC.mapping[formal.itemId] = temp
     of paVarAsgn:
       assert(skipTypes(formal.typ, abstractInst).kind in {tyVar, tyLent})
-      idNodeTablePut(newC.mapping, formal, arg)
+      newC.mapping[formal.itemId] = arg
       # XXX BUG still not correct if the arg has a side effect!
     of paViaIndirection:
       let t = formal.typ
@@ -787,13 +789,13 @@ proc transformFor(c: PTransf, n: PNode): PNode =
       var addrExp = newNodeIT(nkHiddenAddr, formal.info, makeVarType(t.owner, t, c.idgen, tyPtr))
       addrExp.add(arg)
       stmtList.add(newAsgnStmt(c, nkFastAsgn, temp, addrExp, true))
-      idNodeTablePut(newC.mapping, formal, newDeref(temp))
+      newC.mapping[formal.itemId] = newDeref(temp)
     of paComplexOpenarray:
       # arrays will deep copy here (pretty bad).
       var temp = newTemp(c, arg.typ, formal.info)
       addVar(v, temp)
       stmtList.add(newAsgnStmt(c, nkFastAsgn, temp, arg, true))
-      idNodeTablePut(newC.mapping, formal, temp)
+      newC.mapping[formal.itemId] = temp
 
   let body = transformBody(c.graph, c.idgen, iter, {useCache}+c.flags)
   pushInfoContext(c.graph.config, n.info)