diff --git a/liberty/LibertyReader.cc b/liberty/LibertyReader.cc
index 880a682e..156255ad 100644
--- a/liberty/LibertyReader.cc
+++ b/liberty/LibertyReader.cc
@@ -583,7 +583,7 @@ LibertyReader::endLibraryAttrs(LibertyGroup *group)
   // Default resistance_unit to pulling_resistance_unit.
   if (!have_resistance_unit_) {
     Units *units = library_->units();
-    units->resistanceUnit()->copy(units->pullingResistanceUnit());
+    *units->resistanceUnit() = *units->pullingResistanceUnit();
   }
 
   // These attributes reference named groups in the library so
diff --git a/liberty/Units.cc b/liberty/Units.cc
index 42cda577..35815263 100644
--- a/liberty/Units.cc
+++ b/liberty/Units.cc
@@ -47,13 +47,12 @@ Unit::~Unit()
 }
 
 void
-Unit::copy(const Unit *unit)
+Unit::operator=(const Unit &unit)
 {
-  if (suffix_)
-    stringDelete(suffix_);
-  scale_ = unit->scale_;
-  suffix_ = stringCopy(unit->suffix_);
-  digits_ = unit->digits_;
+  scale_ = unit.scale_;
+  stringDelete(suffix_);
+  suffix_ = stringCopy(unit.suffix_);
+  digits_ = unit.digits_;
 }
 
 void
@@ -65,8 +64,7 @@ Unit::setScale(float scale)
 void
 Unit::setSuffix(const char *suffix)
 {
-  if (suffix_)
-    stringDelete(suffix_);
+  stringDelete(suffix_);
   suffix_ = stringCopy(suffix);
 }
 
@@ -134,16 +132,16 @@ Units::find(const char *unit_name)
 }
 
 void
-Units::copy(const Units *units)
+Units::operator=(const Units &units)
 {
-  time_unit_.copy(units->timeUnit());
-  capacitance_unit_.copy(units->capacitanceUnit());
-  resistance_unit_.copy(units->resistanceUnit());
-  voltage_unit_.copy(units->voltageUnit());
-  current_unit_.copy(units->currentUnit());
-  power_unit_.copy(units->powerUnit());
-  distance_unit_.copy(units->distanceUnit());
-  scalar_unit_.copy(units->scalarUnit());
+  time_unit_ = *units.timeUnit();
+  capacitance_unit_ = *units.capacitanceUnit();
+  resistance_unit_ = *units.resistanceUnit();
+  voltage_unit_ = *units.voltageUnit();
+  current_unit_ = *units.currentUnit();
+  power_unit_ = *units.powerUnit();
+  distance_unit_ = *units.distanceUnit();
+  scalar_unit_ = *units.scalarUnit();
 }
 
 } // namespace
diff --git a/liberty/Units.hh b/liberty/Units.hh
index ae2855e3..2d820cbf 100644
--- a/liberty/Units.hh
+++ b/liberty/Units.hh
@@ -17,8 +17,6 @@
 #ifndef STA_UNITS_H
 #define STA_UNITS_H
 
-#include "DisallowCopyAssign.hh"
-
 namespace sta {
 
 class Unit
@@ -29,7 +27,7 @@ public:
   Unit(float scale,
        const char *suffix,
        int digits);
-  void copy(const Unit *unit);
+  void operator=(const Unit &unit);
   float scale() const { return scale_; }
   void setScale(float scale);
   const char *suffix() const { return suffix_; }
@@ -43,8 +41,6 @@ public:
 		       int digits) const;
 
 private:
-  DISALLOW_COPY_AND_ASSIGN(Unit);
-
   float scale_;			// multiplier from user units to internal units
   const char *suffix_;		// print suffix
   int digits_;			// print digits (after decimal pt)
@@ -57,7 +53,7 @@ class Units
 public:
   Units() {}
   Unit *find(const char *unit_name);
-  void copy(const Units *units);
+  void operator=(const Units &units);
   Unit *timeUnit() { return &time_unit_; }
   const Unit *timeUnit() const { return &time_unit_; }
   Unit *capacitanceUnit() { return &capacitance_unit_; }
@@ -78,8 +74,6 @@ public:
   const Unit *scalarUnit() const { return &scalar_unit_; }
 
 private:
-  DISALLOW_COPY_AND_ASSIGN(Units);
-
   Unit time_unit_;
   Unit capacitance_unit_;
   Unit voltage_unit_;
diff --git a/search/CheckMinPulseWidths.cc b/search/CheckMinPulseWidths.cc
index df00ef43..7eef8360 100644
--- a/search/CheckMinPulseWidths.cc
+++ b/search/CheckMinPulseWidths.cc
@@ -358,7 +358,7 @@ MinPulseWidthCheck::closePath(const StaState *sta,
     if (tagMatchNoPathAp(close_path->tag(sta), &close_tag)) {
       debugPrint1(sta->debug(), "mpw", 3, " match %s\n",
 		  close_path->tag(sta)->asString(sta));
-      close.copy(close_path);
+      close = close_path;
       break;
     }
   }
diff --git a/search/ClkSkew.cc b/search/ClkSkew.cc
index d6a268f0..a98c9e48 100644
--- a/search/ClkSkew.cc
+++ b/search/ClkSkew.cc
@@ -45,8 +45,8 @@ public:
   ClkSkew(PathVertex *src_path,
 	  PathVertex *tgt_path,
 	  StaState *sta);
-  ClkSkew(ClkSkew &clk_skew);
-  void copy(ClkSkew &clk_skew);
+  ClkSkew(const ClkSkew &clk_skew);
+  void operator=(const ClkSkew &clk_skew);
   PathVertex *srcPath() { return &src_path_; }
   PathVertex *tgtPath() { return &tgt_path_; }
   float srcLatency(StaState *sta);
@@ -58,8 +58,6 @@ private:
   PathVertex src_path_;
   PathVertex tgt_path_;
   float skew_;
-
-  DISALLOW_COPY_AND_ASSIGN(ClkSkew);
 };
 
 ClkSkew::ClkSkew() :
@@ -71,21 +69,23 @@ ClkSkew::ClkSkew(PathVertex *src_path,
 		 PathVertex *tgt_path,
 		 StaState *sta)
 {
-  src_path_.copy(src_path);
-  tgt_path_.copy(tgt_path);
+  src_path_ = src_path;
+  tgt_path_ = tgt_path;
   skew_ = srcLatency(sta) - tgtLatency(sta) - delayAsFloat(crpr(sta));
 }
 
-ClkSkew::ClkSkew(ClkSkew &clk_skew)
+ClkSkew::ClkSkew(const ClkSkew &clk_skew)
 {
-  copy(clk_skew);
+  src_path_ = clk_skew.src_path_;
+  tgt_path_ = clk_skew.tgt_path_;
+  skew_ = clk_skew.skew_;
 }
 
 void
-ClkSkew::copy(ClkSkew &clk_skew)
+ClkSkew::operator=(const ClkSkew &clk_skew)
 {
-  src_path_.copy(clk_skew.src_path_);
-  tgt_path_.copy(clk_skew.tgt_path_);
+  src_path_ = clk_skew.src_path_;
+  tgt_path_ = clk_skew.tgt_path_;
   skew_ = clk_skew.skew_;
 }
 
@@ -288,7 +288,7 @@ ClkSkews::findClkSkew(Vertex *src_vertex,
 	      skews[src_clk] = clk_skew;
 	    }
 	    else if (fuzzyGreater(probe.skew(), clk_skew->skew()))
-	      clk_skew->copy(probe);
+	      *clk_skew = probe;
 	  }
 	}
       }
diff --git a/search/ClkSkew.hh b/search/ClkSkew.hh
index ef6eff8c..66c57049 100644
--- a/search/ClkSkew.hh
+++ b/search/ClkSkew.hh
@@ -66,4 +66,3 @@ protected:
     
 } // namespace
 #endif
-
diff --git a/search/Crpr.cc b/search/Crpr.cc
index a5e8290f..d49e26fd 100644
--- a/search/Crpr.cc
+++ b/search/Crpr.cc
@@ -198,7 +198,7 @@ CheckCrpr::portClkPath(const ClockEdge *clk_edge,
     PathVertex *path = path_iter.next();
     if (path->clkEdge(this) == clk_edge
 	&& path->isClock(this)) {
-      genclk_path.copy(path);
+      genclk_path = path;
       break;
     }
   }
diff --git a/search/Latches.cc b/search/Latches.cc
index 16714061..18cc1c03 100644
--- a/search/Latches.cc
+++ b/search/Latches.cc
@@ -241,7 +241,7 @@ Latches::latchEnableOtherPath(Path *path,
     PathVertex *path = path_iter.next();
     if (path->isClock(this)
 	&& path->clkEdge(this) == other_clk_edge) {
-      other_path.copy(path);
+      other_path = path;
       break;
     }
   }
@@ -269,7 +269,7 @@ Latches::latchEnablePath(Path *q_path,
       const ClockEdge *clk_edge = path->clkEdge(this);
       if (path->isClock(this)
 	  && clk_edge == en_clk_edge) {
-	enable_path.copy(path);
+	enable_path = path;
 	break;
       }
     }
diff --git a/search/PathEnd.cc b/search/PathEnd.cc
index d4a1ce26..a45adc30 100644
--- a/search/PathEnd.cc
+++ b/search/PathEnd.cc
@@ -298,7 +298,7 @@ PathEnd::clkPath(PathVertex *path,
     p.prevPath(sta, prev_path, prev_arc);
 
     if (p.isClock(sta)) {
-      clk_path.copy(p);
+      clk_path = p;
       return;
     }
     if (prev_arc) {
@@ -306,7 +306,7 @@ PathEnd::clkPath(PathVertex *path,
       if (prev_role == TimingRole::regClkToQ()
 	  || prev_role == TimingRole::latchEnToQ()) {
 	p.prevPath(sta, prev_path, prev_arc);
-	clk_path.copy(prev_path);
+	clk_path = prev_path;
 	return;
       }
       else if (prev_role == TimingRole::latchDtoQ()) {
@@ -314,11 +314,11 @@ PathEnd::clkPath(PathVertex *path,
 	Edge *prev_edge = p.prevEdge(prev_arc, sta);
 	PathVertex enable_path;
 	latches->latchEnablePath(&p, prev_edge, enable_path);
-	clk_path.copy(enable_path);
+	clk_path = enable_path;
 	return;
       }
     }
-    p.copy(prev_path);
+    p = prev_path;
   }
 }
 
@@ -1069,7 +1069,7 @@ PathEndLatchCheck::PathEndLatchCheck(Path *path,
   latches->latchEnableOtherPath(disable_path,
 				disable_path->pathAnalysisPt(sta),
 				enable_path);
-  clk_path_.copy(enable_path);
+  clk_path_ = enable_path;
   Search *search = sta->search();
   // Same as PathEndPathDelay::findRequired.
   if (path_delay_ && path_delay_->ignoreClkLatency())
diff --git a/search/PathRef.cc b/search/PathRef.cc
index 30b1443b..2b77308a 100644
--- a/search/PathRef.cc
+++ b/search/PathRef.cc
@@ -78,13 +78,13 @@ PathRef::init(const PathRef *path)
 void
 PathRef::init(const PathVertex *path)
 {
-  path_vertex_.copy(path);
+  path_vertex_ = path;
 }
 
 void
 PathRef::init(const PathVertex &path)
 {
-  path_vertex_.copy(path);
+  path_vertex_ = path;
 }
 
 void
@@ -105,7 +105,7 @@ PathRef::init(PathEnumed *path)
 void
 PathRef::setRef(PathRef *ref) const
 {
-  ref->path_vertex_.copy(path_vertex_);
+  ref->path_vertex_ = path_vertex_;
   ref->path_enumed_ = path_enumed_;
 }
 
diff --git a/search/PathVertex.cc b/search/PathVertex.cc
index 44bbe0e5..a087c449 100644
--- a/search/PathVertex.cc
+++ b/search/PathVertex.cc
@@ -150,28 +150,13 @@ PathVertex::init(const PathVertexRep &path,
 }
 
 void
-PathVertex::copy(const PathVertex &path)
+PathVertex::operator=(const PathVertex &path)
 {
   vertex_ = path.vertex_;
   tag_ = path.tag_;
   arrival_index_ = path.arrival_index_;
 }
 
-void
-PathVertex::copy(const PathVertex *path)
-{
-  if (path) {
-    vertex_ = path->vertex_;
-    tag_ = path->tag_;
-    arrival_index_ = path->arrival_index_;
-  }
-  else {
-    vertex_ = nullptr;
-    tag_ = nullptr;
-    arrival_index_ = 0;
-  }
-}
-
 bool
 PathVertex::isNull() const
 {
@@ -430,7 +415,7 @@ PrevPathVisitor::visitFromToPath(const Pin *,
     bool arrival_exists;
     from_path->arrivalIndex(arrival_index, arrival_exists);
     if (arrival_exists) {
-      prev_path_.copy(from_path);
+      prev_path_ = from_path;
       prev_arc_ = arc;
       // Stop looking for the previous path/arc.
       return false;
@@ -476,7 +461,7 @@ PathVertex::prevPath(const StaState *sta,
   PrevPred2 pred(sta);
   PrevPathVisitor visitor(this, &pred, sta);
   visitor.visitFaninPaths(vertex(sta));
-  prev_path.copy(visitor.prevPath());
+  prev_path = visitor.prevPath();
   prev_arc = visitor.prevArc();
 }
 
@@ -488,7 +473,7 @@ PathVertex::prevPath(const StaState *sta,
   PrevPred2 pred(sta);
   PrevPathVisitor visitor(this, &pred, sta);
   visitor.visitFaninPaths(vertex(sta));
-  prev_path.copy(visitor.prevPath());
+  prev_path = visitor.prevPath();
 }
 
 void
@@ -588,7 +573,7 @@ VertexPathIterator::findNext()
 PathVertex *
 VertexPathIterator::next()
 {
-  path_.copy(next_);
+  path_ = next_;
   findNext();
   return &path_;
 }
diff --git a/search/PathVertex.hh b/search/PathVertex.hh
index 2f62ebb1..da908b5d 100644
--- a/search/PathVertex.hh
+++ b/search/PathVertex.hh
@@ -54,8 +54,7 @@ public:
   void init(Vertex *vertex,
 	    Tag *tag,
 	    int arrival_index);
-  void copy(const PathVertex &path);
-  void copy(const PathVertex *path);
+  void operator=(const PathVertex &path);
   virtual bool isNull() const;
   virtual void setRef(PathRef *ref) const;
   virtual Vertex *vertex(const StaState *) const { return vertex_; }
diff --git a/search/Sta.cc b/search/Sta.cc
index a75e8d0f..7a4e45d9 100644
--- a/search/Sta.cc
+++ b/search/Sta.cc
@@ -605,7 +605,7 @@ Sta::readLiberty(const char *filename,
       && network_->defaultLibertyLibrary() == nullptr) {
     network_->setDefaultLibertyLibrary(library);
     // Set units from default (first) library.
-    units_->copy(library->units());
+    *units_ = *library->units();
   }
   stats.report("Read liberty");
   return library;