opcode: implement FromString()

pkg/vm/opcode/from_string.go

@@ -0,0 +1,20 @@
+package opcode
+
+import "errors"
+
+var stringToOpcode = make(map[string]Opcode)
+
+func init() {
+	for i := 0; i < 255; i++ {
+		op := Opcode(i)
+		stringToOpcode[op.String()] = op
+	}
+}
+
+// FromString converts string representation to and opcode itself.
+func FromString(s string) (Opcode, error) {
+	if op, ok := stringToOpcode[s]; ok {
+		return op, nil
+	}
+	return 0, errors.New("invalid opcode")
+}

pkg/vm/opcode/opcode_test.go

@@ -4,6 +4,7 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 // Nothing more to test here, really.
@@ -18,3 +19,12 @@ func TestStringer(t *testing.T) {
 		assert.Equal(t, s, o.String())
 	}
 }
+
+func TestFromString(t *testing.T) {
+	_, err := FromString("abcdef")
+	require.Error(t, err)
+
+	op, err := FromString(MUL.String())
+	require.NoError(t, err)
+	require.Equal(t, MUL, op)
+}