What I want is to get the fields of A through B, like
type A struct {
Field_1 string
}
type B struct {
*A
}
fieldsOfA := someMagicFunc(&B{})
You can get the Value reflect object of some variable with reflect.ValueOf().
If you also want to modify the variable or its fields, you have to pass the address (pointer) of the variable to ValueOf(). In this case the Value will belong to the pointer (not the pointed value), but you can use Value.Elem() to "navigate" to the Value of the pointed object.
*A is embedded in B, so fields of A can be referenced from a value of B. You can simply use Value.FieldByName() to access a field by name in order to get or set its value.
So this does the work, try it on Go Playground:
b := B{A: &A{"initial"}}
fmt.Println("Initial value:", *b.A)
v := reflect.ValueOf(&b).Elem()
fmt.Println("Field_1 through reflection:", v.FieldByName("Field_1").String())
v.FieldByName("Field_1").SetString("works")
fmt.Println("After modified through reflection:", *b.A)
Output:
Initial value: {initial}
Field_1 through reflection: initial
After modified through reflection: {works}
I recommend to read this blog post to learn the basics of the reflection in Go: