On Mon, Feb 19, 2018 at 5:14 PM, Doğan Kurt <kultigin....@gmail.com> wrote:
> Hi Burak,
>
> The example objects are very simplified. In real code, there are many more
> object types and some of them looks exactly same. For instance;
>
> type chromeHomepage struct {
> Url string
> File string
> }
>
> type firefoxHomepage struct {
> Url string
> File string
> }
>
> They look exactly same in the json, but clean method for firefox and chrome
> objects are completely different.
In that case, I'd do what you did already. Maybe improve it a bit with
something like below, so you won't need a switch:
var dict map[string]func() interface{}
func init() {
dict=make(map[string]func() interface{})
dict["type1"]=func() interface{} {return type1{}}
dict["type2"]=func() interface{} {return type2{}}
...
}
func unmarshal(...) {
...
for _,d:=range detects {
if x, ok:=dict[d.Type]; ok {
u:=x()
json.Unmarshal( d.Object,&u)
// append u to slice
}
}
>
> On Tuesday, February 20, 2018 at 1:03:51 AM UTC+1, Burak Serdar wrote:
>>
>> On Mon, Feb 19, 2018 at 4:45 PM, Doğan Kurt <kultig...@gmail.com> wrote:
>> > Hi great Go community. Sorry it's a long question, but i would really
>> > appreciate some guidance.
>> >
>> >
>> > --------------------
>> >
>> >
>> > Let's say i have two different objects, browser and executable that
>> > implement ScanCleaner interface.
>> >
>> > type ScanCleaner interface {
>> > scan()
>> > clean()
>> > }
>> >
>> > type browser struct {
>> > Name string
>> > }
>> >
>> > type exe struct {
>> > Size int
>> > }
>> >
>> > These two objects are different internally but they implement the same
>> > scan
>> > and clean methods. In general i don't need to know their internals. I
>> > have
>> > this instead;
>> >
>> > var objects []ScanCleaner
>> >
>> > I can iterate through the objects, scan and clean them. So far so good,
>> > but
>> > i want to decouple scan and clean processes. One can scan the system,
>> > get a
>> > report and later clean based on that report file. So that interface
>> > slice
>> > should be stored appropriately in a file and recovered later.
>> >
>> > I encode the objects slice, and get a perfectly good json output.
>> >
>> > Here is the working code: https://play.golang.org/p/cYgnhgxkPL0
>> >
>> > Output:
>> > [{"Name":"chrome"},{"Name":"firefox"},{"Size":1234},{"Size":4321}]
>> >
>> > --------------------
>> >
>> >
>> > The problem arises when i need to decode report file and recover the
>> > objects
>> > interface slice. Object types are completely lost.
>>
>>
>> You can use an intermediate structure to parse the JSON input, and
>> then process that to construct the slice:
>>
>> var entry []struct {
>> Name string
>> Size int
>> ..
>> }
>>
>> json.Unmarshal(&entry)
>> for _,e:=range entry {
>> if len(e.Name)==0 {
>> ... // This entry has size, create struct exe
>> } else {
>> ... // This entry has name, create struct Browser
>> }
>> }
>>
>> Of course, this assumes you can deduce the type of the element based
>> on its contents easily.
>>
>>
>> >
>> > My current solution is this; I encapsulate every object with a string
>> > that
>> > specifies it's type,
>> >
>> > type detection struct {
>> > Type string
>> > Object ScanCleaner
>> > }
>> >
>> > and encode the slice of detection instead. The Type string is main.exe
>> > or
>> > main.browser obtained by fmt.Sprintf("%T", obj).
>> >
>> > Here is a working code: https://play.golang.org/p/KeJjl8IOqRP
>> >
>> > Output:
>> >
>> > [{"Type":"main.browser","Object":{"Name":"chrome"}},{"Type":"main.exe","Object":{"Size":1234}}]
>> >
>> > Finally, i use a dispatch routine that recognizes objects type by Type
>> > string, decodes the object with the correct type, and calls it's clean
>> > method.
>> >
>> > func cleanAll(jsn []byte) {
>> > detects := []struct {
>> > Type string
>> > Object json.RawMessage
>> > }{}
>> >
>> > json.Unmarshal(jsn, &detects)
>> >
>> > for _, d := range detects {
>> > var sc ScanCleaner
>> > switch d.Type {
>> > case "main.exe":
>> > var e exe
>> > json.Unmarshal(d.Object, &e)
>> > sc = e
>> > case "main.browser":
>> > var b browser
>> > json.Unmarshal(d.Object, &b)
>> > sc = b
>> > }
>> > sc.clean()
>> > }
>> > }
>> >
>> > Here is the final working code: https://play.golang.org/p/HpHFiHrT2oz
>> >
>> > Output:
>> >
>> > browser clean {chrome}
>> > browser clean {firefox}
>> > exe clean {1234}
>> > exe clean {4321}
>> >
>> >
>> > --------------------
>> >
>> >
>> > This solution is obviously not good. If i change an objects name, i
>> > should
>> > change the Type string in switch. Also i need to rely on the string
>> > returned
>> > by fmt.Sprintf("%T").
>> >
>> > Is there a better solution to accomplish this task?
>> >
>> > Thanks.
>> >
>> > --
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>> > Groups
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>> > email to golang-nuts...@googlegroups.com.
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>
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