How to initialize a struct value fields using reflection?

Question

I got a .ini configuration file that I want to use to initialize a Configuration struct.

I'd like to use the Configuration fields names and loop over them to populate my new instance with the corresponding value in the .ini file.

I thought the best way to achieve this might be reflection API (maybe I'm totally wrong, tell me...)

My problem here is that I cannot figure out how to access field's name (if it is at least possible)

Here is my code:

package test
import(
     "reflect"
     "gopkg.in/ini.v1"
 )

type Config struct {
    certPath string
    keyPath  string
    caPath   string
}

func InitConfig(iniConf *ini.File) *Config{
    config:=new(Config)
    var valuePtr reflect.Value = reflect.ValueOf(config)
    var value reflect.Value = valuePtr.Elem()
    for i := 0; i < value.NumField(); i++ {
        field := value.Field(i)
        if field.Type() == reflect.TypeOf("") {
            //here is my problem, I can't get the field name, this method does not exist... :'(
            value:=cfg.GetSection("section").GetKey(field.GetName())
            field.SetString(value)
        }
    }
    return config
}

Any help appreciated...

score 2 · Accepted Answer · 2016-02-01 18:29:09Z

2

Use the type to get a StructField. The StructField has the name:

 name := value.Type().Field(i).Name

Note that the ini package's File.MapTo and Section.MapTo methods implement this functionality.

edited Feb 1, 2016 at 18:29

answered Jan 31, 2016 at 16:16

user5728991

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2 Comments

n00dl3 Over a year ago

hmmm... I think I get it, thank you. Another last question, is there another way to achieve this without reflection api ?

n00dl3 Over a year ago

Oh... Indeed, I didn't see that method. Thanks for the tips.

kostix · Accepted Answer · 2016-02-01 18:16:12Z

1

While @MuffinTop solved your immediate issue, I'd say you may be solving a wrong problem. I personally know of at least two packages, github.com/Thomasdezeeuw/ini and gopkg.in/gcfg.v1, which are able to parse INI-style files (of the various level of "INI-ness", FWIW) and automatically populate your struct-typed values using reflection, so for you it merely amounts to properly setting tags on the fields of your struct (if needed at all).

I used both of these packages in production so am able to immediately recommend them. You might find more packages dedicated to parsing INI files on godoc.org.

edited Feb 1, 2016 at 18:16

answered Feb 1, 2016 at 14:43

kostix

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3 Comments

n00dl3 Over a year ago

actualy @MuffinTop pointed this out in the comments. I was pretty sure it existed such implementations, but as a real Go-newbie, I was more curious about the underlying bare-metal way as it's a common process to assing values to dynamic Object/Struct properties. Anyway, I agree with you, it's much cleaner using libraries's built-in mapping functionality. Thanks for taking the time to answer.

kostix Over a year ago

@n00dl3, oh silly me: I got so fixated on your direct usage of reflection I did not spot you were already using gopkg.in/ini.v1 to parse your INI data! So yeah, the @MuffinTop's answer plus their comment is a spot-on.

kostix Over a year ago

JFTR: the gopkg.in/ini.v1 package wasn't among those I recommended because in my personal opinion that package is a prime example of typical overengeneering with its built-in locking for serializing R/W access being a clear Go anti-pattern. It's okay for a start though so don't bother with this for now, @n00dl3, so long it works ;-)

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