merge identical cases for getting operator functions

Author: itchyny

operator.go

@@ -156,19 +156,15 @@ func (op Operator) GoString() (str string) {
 
 func (op Operator) getFunc() string {
 switch op {
-case OpPipe:
-panic("unreachable")
-case OpComma:
-panic("unreachable")
-case OpAdd:
+case OpAdd, OpUpdateAdd:
 return "_add"
-case OpSub:
+case OpSub, OpUpdateSub:
 return "_subtract"
-case OpMul:
+case OpMul, OpUpdateMul:
 return "_multiply"
-case OpDiv:
+case OpDiv, OpUpdateDiv:
 return "_divide"
-case OpMod:
+case OpMod, OpUpdateMod:
 return "_modulo"
 case OpEq:
 return "_equal"
@@ -182,26 +178,10 @@ func (op Operator) getFunc() string {
 return "_greatereq"
 case OpLe:
 return "_lesseq"
-case OpAnd:
-panic("unreachable")
-case OpOr:
-panic("unreachable")
-case OpAlt:
-panic("unreachable")
 case OpAssign:
 return "_assign"
 case OpModify:
 return "_modify"
-case OpUpdateAdd:
-return "_add"
-case OpUpdateSub:
-return "_subtract"
-case OpUpdateMul:
-return "_multiply"
-case OpUpdateDiv:
-return "_divide"
-case OpUpdateMod:
-return "_modulo"
 case OpUpdateAlt:
 return "_alternative"
 default: