Mixing
Dereference struct pointer and access fields with reflection
I'm writing a recursive function that iterates through every primitive field in a struct.
I need to be able to support fields that are structs, pointers to structs, fields, and pointers to fields.
I've tried doing something like this, where for each field, I first do a check if it's a pointer. If it is, I switch on the type of that instead of just the field itself.
//Get reflect values and types
valOf := reflect.ValueOf(dest).Elem()
typeOf := valOf.Type()
//Iterate through each field
for i := 0; i < valOf.NumField(); i++ {
var fieldValDeref reflect.Value
//Get reflect value and type of single field
fieldVal := valOf.Field(i)
fieldTyp := typeOf.Field(i)
//Check if field is a pointer. If so, dereference and switch on dereferenced type
if fieldVal.Kind() == reflect.Ptr {
fieldValDeref = fieldVal.Elem()
} else {
fieldValDeref = fieldVal
}
switch fieldValDeref.Kind() {
case reflect.Array, reflect.Chan, reflect.Interface, reflect.Func, reflect.Map, reflect.UnsafePointer:
return errors.New("invalid destination field: " + fieldTyp.Name)
case reflect.Struct:
//Recursive call
break
default:
//Perform Action on Field
..................................
The issue I'm getting with this, is that the type of any pointer, struct or not, after calling .Elem() is reflect.Invalid.
How can I first dereference a field (if it is a pointer) and then perform actions accordingly, whether the field is a struct or a primitive?
Thanks
go reflection
asked Jan 2 at 20:28
robbieperry22robbieperry22
192117
add a comment |
I'm writing a recursive function that iterates through every primitive field in a struct.
I need to be able to support fields that are structs, pointers to structs, fields, and pointers to fields.
I've tried doing something like this, where for each field, I first do a check if it's a pointer. If it is, I switch on the type of that instead of just the field itself.
//Get reflect values and types
valOf := reflect.ValueOf(dest).Elem()
typeOf := valOf.Type()
//Iterate through each field
for i := 0; i < valOf.NumField(); i++ {
var fieldValDeref reflect.Value
//Get reflect value and type of single field
fieldVal := valOf.Field(i)
fieldTyp := typeOf.Field(i)
//Check if field is a pointer. If so, dereference and switch on dereferenced type
if fieldVal.Kind() == reflect.Ptr {
fieldValDeref = fieldVal.Elem()
} else {
fieldValDeref = fieldVal
}
switch fieldValDeref.Kind() {
case reflect.Array, reflect.Chan, reflect.Interface, reflect.Func, reflect.Map, reflect.UnsafePointer:
return errors.New("invalid destination field: " + fieldTyp.Name)
case reflect.Struct:
//Recursive call
break
default:
//Perform Action on Field
..................................
The issue I'm getting with this, is that the type of any pointer, struct or not, after calling .Elem() is reflect.Invalid.
How can I first dereference a field (if it is a pointer) and then perform actions accordingly, whether the field is a struct or a primitive?
Thanks
go reflection
asked Jan 2 at 20:28
robbieperry22robbieperry22
192117
2
Dereferencing an uninitialized, ienil, pointer will always result inreflect.Invalid. See here (play.golang.com/p/8UgDtqK_8ra). To avoid this you have to initialize the field's value which you can do withreflect.New
– mkopriva
Jan 2 at 20:54
... here's an example: play.golang.com/p/q71J0qTQECP
– mkopriva
Jan 2 at 20:58
Would reflectively creating a zero value instance of it first before dereferencing solve this?
– robbieperry22
Jan 2 at 20:59
Does the code in the second comment not already answer your question?
– mkopriva
Jan 2 at 21:03
1
It does, thanks. Comments didn't refresh when I replied.
– robbieperry22
Jan 2 at 21:11
add a comment |
I'm writing a recursive function that iterates through every primitive field in a struct.
I need to be able to support fields that are structs, pointers to structs, fields, and pointers to fields.
I've tried doing something like this, where for each field, I first do a check if it's a pointer. If it is, I switch on the type of that instead of just the field itself.
//Get reflect values and types
valOf := reflect.ValueOf(dest).Elem()
typeOf := valOf.Type()
//Iterate through each field
for i := 0; i < valOf.NumField(); i++ {
var fieldValDeref reflect.Value
//Get reflect value and type of single field
fieldVal := valOf.Field(i)
fieldTyp := typeOf.Field(i)
//Check if field is a pointer. If so, dereference and switch on dereferenced type
if fieldVal.Kind() == reflect.Ptr {
fieldValDeref = fieldVal.Elem()
} else {
fieldValDeref = fieldVal
}
switch fieldValDeref.Kind() {
case reflect.Array, reflect.Chan, reflect.Interface, reflect.Func, reflect.Map, reflect.UnsafePointer:
return errors.New("invalid destination field: " + fieldTyp.Name)
case reflect.Struct:
//Recursive call
break
default:
//Perform Action on Field
..................................
The issue I'm getting with this, is that the type of any pointer, struct or not, after calling .Elem() is reflect.Invalid.
How can I first dereference a field (if it is a pointer) and then perform actions accordingly, whether the field is a struct or a primitive?
Thanks
go reflection
asked Jan 2 at 20:28
robbieperry22robbieperry22
192117
I'm writing a recursive function that iterates through every primitive field in a struct.
I need to be able to support fields that are structs, pointers to structs, fields, and pointers to fields.
I've tried doing something like this, where for each field, I first do a check if it's a pointer. If it is, I switch on the type of that instead of just the field itself.
//Get reflect values and types
valOf := reflect.ValueOf(dest).Elem()
typeOf := valOf.Type()
//Iterate through each field
for i := 0; i < valOf.NumField(); i++ {
var fieldValDeref reflect.Value
//Get reflect value and type of single field
fieldVal := valOf.Field(i)
fieldTyp := typeOf.Field(i)
//Check if field is a pointer. If so, dereference and switch on dereferenced type
if fieldVal.Kind() == reflect.Ptr {
fieldValDeref = fieldVal.Elem()
} else {
fieldValDeref = fieldVal
}
switch fieldValDeref.Kind() {
case reflect.Array, reflect.Chan, reflect.Interface, reflect.Func, reflect.Map, reflect.UnsafePointer:
return errors.New("invalid destination field: " + fieldTyp.Name)
case reflect.Struct:
//Recursive call
break
default:
//Perform Action on Field
..................................
The issue I'm getting with this, is that the type of any pointer, struct or not, after calling .Elem() is reflect.Invalid.
How can I first dereference a field (if it is a pointer) and then perform actions accordingly, whether the field is a struct or a primitive?
Thanks
go reflection
go reflection
asked Jan 2 at 20:28
robbieperry22robbieperry22
192117
asked Jan 2 at 20:28
robbieperry22robbieperry22
192117
asked Jan 2 at 20:28
robbieperry22robbieperry22
192117
asked Jan 2 at 20:28
robbieperry22robbieperry22
192117
asked Jan 2 at 20:28
robbieperry22robbieperry22
192117
192117
2
Dereferencing an uninitialized, ienil, pointer will always result inreflect.Invalid. See here (play.golang.com/p/8UgDtqK_8ra). To avoid this you have to initialize the field's value which you can do withreflect.New
– mkopriva
Jan 2 at 20:54
... here's an example: play.golang.com/p/q71J0qTQECP
– mkopriva
Jan 2 at 20:58
Would reflectively creating a zero value instance of it first before dereferencing solve this?
– robbieperry22
Jan 2 at 20:59
Does the code in the second comment not already answer your question?
– mkopriva
Jan 2 at 21:03
1
It does, thanks. Comments didn't refresh when I replied.
– robbieperry22
Jan 2 at 21:11
add a comment |
2
Dereferencing an uninitialized, ienil, pointer will always result inreflect.Invalid. See here (play.golang.com/p/8UgDtqK_8ra). To avoid this you have to initialize the field's value which you can do withreflect.New
– mkopriva
Jan 2 at 20:54
... here's an example: play.golang.com/p/q71J0qTQECP
– mkopriva
Jan 2 at 20:58
Would reflectively creating a zero value instance of it first before dereferencing solve this?
– robbieperry22
Jan 2 at 20:59
Does the code in the second comment not already answer your question?
– mkopriva
Jan 2 at 21:03
1
It does, thanks. Comments didn't refresh when I replied.
– robbieperry22
Jan 2 at 21:11
2
2
Dereferencing an uninitialized, ie
nil, pointer will always result in reflect.Invalid. See here (play.golang.com/p/8UgDtqK_8ra). To avoid this you have to initialize the field's value which you can do with reflect.New– mkopriva
Jan 2 at 20:54
Dereferencing an uninitialized, ie
nil, pointer will always result in reflect.Invalid. See here (play.golang.com/p/8UgDtqK_8ra). To avoid this you have to initialize the field's value which you can do with reflect.New– mkopriva
Jan 2 at 20:54
... here's an example: play.golang.com/p/q71J0qTQECP
– mkopriva
Jan 2 at 20:58
... here's an example: play.golang.com/p/q71J0qTQECP
– mkopriva
Jan 2 at 20:58
Would reflectively creating a zero value instance of it first before dereferencing solve this?
– robbieperry22
Jan 2 at 20:59
Would reflectively creating a zero value instance of it first before dereferencing solve this?
– robbieperry22
Jan 2 at 20:59
Does the code in the second comment not already answer your question?
– mkopriva
Jan 2 at 21:03
Does the code in the second comment not already answer your question?
– mkopriva
Jan 2 at 21:03
1
1
It does, thanks. Comments didn't refresh when I replied.
– robbieperry22
Jan 2 at 21:11
It does, thanks. Comments didn't refresh when I replied.
– robbieperry22
Jan 2 at 21:11
add a comment |
1 Answer
1
active
oldest
votes
As mkopriva mentioned, dereferencing a nil pointer will always return reflect.Invalid. The solution is to create a new instance first.
if fieldVal.Kind() == reflect.Ptr {
fieldVal.Set(reflect.New(fieldVal.Type().Elem()))
fieldValDeref = fieldVal.Elem()
} else {
fieldValDeref = fieldVal
}
answered Jan 2 at 21:16
robbieperry22robbieperry22
192117
add a comment |
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1 Answer
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1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
As mkopriva mentioned, dereferencing a nil pointer will always return reflect.Invalid. The solution is to create a new instance first.
if fieldVal.Kind() == reflect.Ptr {
fieldVal.Set(reflect.New(fieldVal.Type().Elem()))
fieldValDeref = fieldVal.Elem()
} else {
fieldValDeref = fieldVal
}
answered Jan 2 at 21:16
robbieperry22robbieperry22
192117
add a comment |
As mkopriva mentioned, dereferencing a nil pointer will always return reflect.Invalid. The solution is to create a new instance first.
if fieldVal.Kind() == reflect.Ptr {
fieldVal.Set(reflect.New(fieldVal.Type().Elem()))
fieldValDeref = fieldVal.Elem()
} else {
fieldValDeref = fieldVal
}
answered Jan 2 at 21:16
robbieperry22robbieperry22
192117
add a comment |
As mkopriva mentioned, dereferencing a nil pointer will always return reflect.Invalid. The solution is to create a new instance first.
if fieldVal.Kind() == reflect.Ptr {
fieldVal.Set(reflect.New(fieldVal.Type().Elem()))
fieldValDeref = fieldVal.Elem()
} else {
fieldValDeref = fieldVal
}
answered Jan 2 at 21:16
robbieperry22robbieperry22
192117
As mkopriva mentioned, dereferencing a nil pointer will always return reflect.Invalid. The solution is to create a new instance first.
if fieldVal.Kind() == reflect.Ptr {
fieldVal.Set(reflect.New(fieldVal.Type().Elem()))
fieldValDeref = fieldVal.Elem()
} else {
fieldValDeref = fieldVal
}
answered Jan 2 at 21:16
robbieperry22robbieperry22
192117
answered Jan 2 at 21:16
robbieperry22robbieperry22
192117
answered Jan 2 at 21:16
robbieperry22robbieperry22
192117
answered Jan 2 at 21:16
robbieperry22robbieperry22
192117
192117
add a comment |
add a comment |
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2
Dereferencing an uninitialized, ie
nil, pointer will always result inreflect.Invalid. See here (play.golang.com/p/8UgDtqK_8ra). To avoid this you have to initialize the field's value which you can do withreflect.New– mkopriva
Jan 2 at 20:54
... here's an example: play.golang.com/p/q71J0qTQECP
– mkopriva
Jan 2 at 20:58
Would reflectively creating a zero value instance of it first before dereferencing solve this?
– robbieperry22
Jan 2 at 20:59
Does the code in the second comment not already answer your question?
– mkopriva
Jan 2 at 21:03
1
It does, thanks. Comments didn't refresh when I replied.
– robbieperry22
Jan 2 at 21:11