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Handling Null JSON Arrays in Go - Performance
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package main | |
import ( | |
"encoding/json" | |
"fmt" | |
"reflect" | |
"time" | |
) | |
// Bag holds items | |
type Bag struct { | |
Name string | |
Items []string | |
} | |
// BagAlias is a bag that does not implement the Marshaler interface | |
type BagAlias Bag | |
// MarshalJSON initializes nil slices and then marshals the bag to JSON | |
func (b Bag) MarshalJSON() ([]byte, error) { | |
a := struct { | |
BagAlias | |
}{ | |
BagAlias: (BagAlias)(b), | |
} | |
if a.Items == nil { | |
a.Items = make([]string, 0) | |
} | |
return json.Marshal(a) | |
} | |
// NilSliceToEmptySlice recursively sets nil slices to empty slices | |
func NilSliceToEmptySlice(inter interface{}) interface{} { | |
// original input that can't be modified | |
val := reflect.ValueOf(inter) | |
switch val.Kind() { | |
case reflect.Slice: | |
newSlice := reflect.MakeSlice(val.Type(), 0, val.Len()) | |
if !val.IsZero() { | |
// iterate over each element in slice | |
for j := 0; j < val.Len(); j++ { | |
item := val.Index(j) | |
var newItem reflect.Value | |
switch item.Kind() { | |
case reflect.Struct: | |
// recursively handle nested struct | |
newItem = reflect.Indirect(reflect.ValueOf(NilSliceToEmptySlice(item.Interface()))) | |
default: | |
newItem = item | |
} | |
newSlice = reflect.Append(newSlice, newItem) | |
} | |
} | |
return newSlice.Interface() | |
case reflect.Struct: | |
// new struct that will be returned | |
newStruct := reflect.New(reflect.TypeOf(inter)) | |
newVal := newStruct.Elem() | |
// iterate over input's fields | |
for i := 0; i < val.NumField(); i++ { | |
newValField := newVal.Field(i) | |
valField := val.Field(i) | |
switch valField.Kind() { | |
case reflect.Slice: | |
// recursively handle nested slice | |
newValField.Set(reflect.Indirect(reflect.ValueOf(NilSliceToEmptySlice(valField.Interface())))) | |
case reflect.Struct: | |
// recursively handle nested struct | |
newValField.Set(reflect.Indirect(reflect.ValueOf(NilSliceToEmptySlice(valField.Interface())))) | |
default: | |
newValField.Set(valField) | |
} | |
} | |
return newStruct.Interface() | |
case reflect.Map: | |
// new map to be returned | |
newMap := reflect.MakeMap(reflect.TypeOf(inter)) | |
// iterate over every key value pair in input map | |
iter := val.MapRange() | |
for iter.Next() { | |
k := iter.Key() | |
v := iter.Value() | |
// recursively handle nested value | |
newV := reflect.Indirect(reflect.ValueOf(NilSliceToEmptySlice(v.Interface()))) | |
newMap.SetMapIndex(k, newV) | |
} | |
return newMap.Interface() | |
case reflect.Ptr: | |
// dereference pointer | |
return NilSliceToEmptySlice(val.Elem().Interface()) | |
default: | |
return inter | |
} | |
} | |
// TimeIt runs f and returns how long it took | |
func TimeIt(f func()) time.Duration { | |
startTime := time.Now() | |
f() | |
endTime := time.Now() | |
return endTime.Sub(startTime) | |
} | |
func main() { | |
var diff time.Duration | |
length := 100000 | |
items := []string{"item1", "item2", "item3"} | |
lotsOfBags := make([]BagAlias, length) | |
for i := range lotsOfBags { | |
lotsOfBags[i] = BagAlias{Items: items} | |
} | |
diff = TimeIt(func() { | |
newLotsOfBags := NilSliceToEmptySlice(lotsOfBags) | |
json.Marshal(newLotsOfBags) | |
}) | |
fmt.Printf("NilSliceToEmptySlice() took %d milliseconds to process %d bags\n", diff.Milliseconds(), length) | |
bags := make([]Bag, length) | |
for i := range bags { | |
bags[i] = Bag{Items: items} | |
} | |
diff = TimeIt(func() { | |
json.Marshal(bags) | |
}) | |
fmt.Printf("MarshalJSON() took %d milliseconds to process %d bags\n", diff.Milliseconds(), length) | |
} |
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