CODEWITHSUNDEEP
reflectionstructgo
DonSeba
DonSeba

Reputation: 2119

GO Golang : anonymous structs & Reflection combination

After reading the laws of reflection about 10 times the last 2 months. Developing with it for the same amount of time, i have to say it is a cool and understandable language... at least to an certain level.

My background as PHP & Javascript developer are giving me an hard time to comprehend the following example: 

package main

import(
    "fmt"
    "reflect"
)


func test1(){
    type template struct {
        Title string
        Body  string
    }

    data := []template{
        { Title : "About page", Body : "Body info"},
        { Body : "About page 2 ", Title : "Body info 2"},
    }

    fmt.Println( "-- TEST ONE --" ) 
    fmt.Println( data[0].Title )
}

func test2(){
    data := []struct{
        Title string
        Body  string
    }{
        // Assign with the actual order
        { "About page", "Body info"},
        // Key => Val assignment (Pretty cool)
        { Body : "Body info 2 ", Title : "About page 2"},
    }

    fmt.Println( "-- TEST TWO --" ) 
    fmt.Println( data[1].Title )
}

func test3(){
    type template struct {
        Title string
        Body  string
    }

    Amap := map[string]interface{}{
        "template" : template{},
    }

    w := reflect.ValueOf(Amap["template"])
    x := w.Type()
    y := reflect.TypeOf(w.Interface())
    z := reflect.TypeOf(Amap["template"])

    fmt.Printf("%+v\n", x) // main.template
    fmt.Printf("%+v\n", y) // main.template
    fmt.Printf("%+v\n", z) // main.template

    /*
    var data = struct{
        // none of the above can be place in here.... ( (w|x|y|z) is not a type)
    }{ "About page", "Body info"}
    */

    ww := reflect.New(z)
    xx := ww.Interface()
    tt := reflect.TypeOf(xx)

    /*
    // none of the above can be used this way....
    var data = ww{

    }{ "About page", "Body info"}
    */

    fmt.Println( "-- TEST THREE --" ) 
    fmt.Println( data.Title )
}

func main(){
    test1()
    test2()
    test3()
}

The above example test1() and test2() work as expected. I wanted to push it even further with test3() but without success. The only way i could think of making it work was with an type switch..

But since I am trying things out I'd like to know if :

  1. Is there an way to cast an anonymous struct from an reflection value without type checking the actual struct that is being reflected
  2. Could you show me an working solution to either one of the 2 commented out code blocks from test3()

Upvotes: 2

Views: 2125

Answers (1)

thwd
thwd

Reputation: 24878

  1. Is there a way to cast 1 an anonymous struct from an reflection value without type checking [2] the actual struct that is being reflected?
  1. There is no casting in Go. If you mean a conversion then you're missing a predicate: convert to what?
  2. Type checking is something a compiler does to a program. This sentence does not make sense.
  1. Could you show me a working solution to either one of the 2 commented out code blocks from test3()

That's simple, just write:

var data = struct{string, string}{"About page", "Body info"}

If you mean to build/create/assemble a struct type on runtime I'll have to disappoint you; that's not possible.

Edit (11. Feb 2015): building struct types (as well as arrays, funcs and interfaces) on runtime by means of reflection is being implemented.

Upvotes: 3

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