minor cleanup, update to qalloc for qcor

Signed-off-by: Alex McCaskey <mccaskeyaj@ornl.gov>

quantum/gate/ir/Gate.hpp

@@ -81,7 +81,7 @@ public:
     bitIdxExpressions.insert({bit_idx, expr});
   }
   std::string getBitExpression(const std::size_t bit_idx) override {
-    return bitIdxExpressions[bit_idx];
+    return bitIdxExpressions.count(bit_idx) ? bitIdxExpressions[bit_idx] : "";
   }
 
   const InstructionParameter getParameter(const std::size_t idx) const override;

xacc/compiler/Compiler.hpp

@@ -28,6 +28,10 @@ public:
                                       std::shared_ptr<Accelerator> acc) = 0;
   virtual std::shared_ptr<IR> compile(const std::string &src) = 0;
   
+  virtual const std::string get_statement_terminator() {
+      return ";";
+  }
+  
   // By default, we assume this compiler can not parse a given 
   // source string. Subtypes implement this to indicate if 
   // they can or not

xacc/compiler/qalloc.cpp

@@ -10,7 +10,9 @@ template <typename T> struct empty_delete {
 qreg::qreg(const int n) { buffer = xacc::qalloc(n).get(); }
 qreg::qreg(const qreg &other) : buffer(other.buffer) {}
 
-int qreg::operator[](const int &i) { return i; }
+qubit qreg::operator[](const std::size_t &i) {
+  return std::make_pair(buffer->name(), i);
+}
 AcceleratorBuffer *qreg::results() { return buffer; }
 std::map<std::string, int> qreg::counts() {
   return buffer->getMeasurementCounts();

xacc/compiler/qalloc.hpp

@@ -19,6 +19,7 @@ namespace xacc {
 class AcceleratorBuffer;
 class Observable;
 namespace internal_compiler {
+using qubit = std::pair<std::string, std::size_t>;
 
 class qreg {
 protected:
@@ -28,7 +29,7 @@ public:
   qreg() = default;
   qreg(const int n);
   qreg (const qreg& other);
-  int operator[](const int &i);
+  qubit operator[](const std::size_t &i);
   AcceleratorBuffer *results();
   std::map<std::string, int> counts();
   double exp_val_z();

xacc/xacc.hpp

@@ -247,7 +247,7 @@ const std::string
 translate(std::shared_ptr<CompositeInstruction> CompositeInstruction,
           const std::string toLanguage);
 
-void appendCompiled(std::shared_ptr<CompositeInstruction> composite, bool _override = false);
+void appendCompiled(std::shared_ptr<CompositeInstruction> composite, bool _override = true);
 std::shared_ptr<CompositeInstruction> getCompiled(const std::string name);
 bool hasCompiled(const std::string name);