perf: minimize assertion calls and reduce overhead (#107)

perf: #94

Signed-off-by: lookupman <[email protected]>

opengemini/measurement.go

@@ -64,10 +64,11 @@ func (c *client) ShowSeries(database, command string) ([]string, error) {
 		return []string{}, nil
 	}
 	for _, v := range seriesResult[0].Values {
-		if _, ok := v.(string); !ok {
+		strV, ok := v.(string)
+		if !ok {
 			return series, nil
 		}
-		series = append(series, v.(string))
+		series = append(series, strV)
 	}
 	return series, nil
 }

opengemini/query.go

@@ -110,10 +110,11 @@ func (c *client) showTagSeriesQuery(database, command string) ([]ValuesResult, e
 		tagSeriesRes.Measurement = res.Name
 		for _, valRes := range res.Values {
 			for _, value := range valRes {
-				if _, ok := value.(string); !ok {
+				strVal, ok := value.(string)
+				if !ok {
 					return tagSeries, nil
 				}
-				tagSeriesRes.Values = append(tagSeriesRes.Values, value.(string))
+				tagSeriesRes.Values = append(tagSeriesRes.Values, strVal)
 			}
 		}
 		tagSeries = append(tagSeries, *tagSeriesRes)
@@ -143,11 +144,11 @@ func (c *client) showTagFieldQuery(database, command string) ([]ValuesResult, er
 			if len(valRes) < 2 {
 				return tagValueResult, nil
 			}
-			if _, ok := valRes[0].(string); ok {
-				tagValue.Name = valRes[0].(string)
+			if strVal, ok := valRes[0].(string); ok {
+				tagValue.Name = strVal
 			}
-			if _, ok := valRes[1].(string); ok {
-				tagValue.Value = valRes[1].(string)
+			if strVal, ok := valRes[1].(string); ok {
+				tagValue.Value = strVal
 			}
 			tagValueRes.Values = append(tagValueRes.Values, *tagValue)
 		}