Simplified code

A const_cast that was apparently a residual of older implementations

src/tools/SwitchingFunction.cpp

@@ -278,9 +278,9 @@ void SwitchingFunction::set(const std::string & definition,std::string& errormsg
 // e.g. func=0*x
         lepton_ref[t]=nullptr;
       } else if(vars.size()==1 && found_x) {
-        lepton_ref[t]=&const_cast<lepton::CompiledExpression*>(&expression[t])->getVariableReference("x");
+        lepton_ref[t]=&expression[t].getVariableReference("x");
       } else if(vars.size()==1 && found_x2) {
-        lepton_ref[t]=&const_cast<lepton::CompiledExpression*>(&expression[t])->getVariableReference("x2");
+        lepton_ref[t]=&expression[t].getVariableReference("x2");
         leptonx2=true;
       } else if(vars.size()==2 && found_x && found_x2) {
         plumed_error() << "Cannot use simultaneously x and x2 argument in switching function: "<<func;
@@ -296,7 +296,7 @@ void SwitchingFunction::set(const std::string & definition,std::string& errormsg
     lepton_ref_deriv.resize(expression_deriv.size());
     for(unsigned t=0; t<lepton_ref_deriv.size(); t++) {
       try {
-        lepton_ref_deriv[t]=&const_cast<lepton::CompiledExpression*>(&expression_deriv[t])->getVariableReference(arg);
+        lepton_ref_deriv[t]=&expression_deriv[t].getVariableReference(arg);
       } catch(const PLMD::lepton::Exception& exc) {
 // this is necessary since in some cases lepton things a variable is not present even though it is present
 // e.g. func=3*x