Problem using go-ini's mapTo function with embedded struct

Question

I'm new to Golang, so I think I'm doing something wrong using go-ini library to read a config file and map it to an embedded struct. I didn't find any working example searching on google, so I would be very happy to get some help here.

My test program works if I use the type "EmbeddedTestData" as a parameter in the "mapTo" call, but if I use the type "TestData" which contains the embedded type, the variable "data" is empty at the end.

/*
config.ini contains following example data:

[clientServer]
Port = ":1111"
WsPath = "/ws"

[courtServer]
port = ":2222"
wsPath = "/cs"
*/

package main

import (
    "fmt"
    "github.com/go-ini/ini"
    "os"
)

type TestData struct {
    EmbeddedTestData
}

type EmbeddedTestData struct {
    Port   string
    WsPath string
}

func main() {
    // load ini-file

    inidata, err := ini.Load("config.ini")

    if err != nil {
        fmt.Printf("Fail to read file: %v", err)
        os.Exit(1)
    }
    // data := new(EmbeddedTestData) -> this works fine!
    data := new(TestData) // doesn't work -> Content in variable 'data':  &{{ }}
    err = inidata.Section("clientServer").MapTo(data)
    fmt.Println("Content in variable 'data': ", data)
}

I would expect that variable "data" in the end contains the mapped data for Port/WsPath from the corresponding section in the config file in case I use type "TestData".

Answer 1

I am a new Golang learner too but i find a fix for your code the first problem in your code is

type TestData struct {
    EmbeddedTestData
}

To define a struct you should use

type <name> struct {
 // field1 type
 // field2 type
 // field3 type
 // ...
}

but you don't give a name to your type

so let's change it and give it a name so we can access the EmbeddedTestData struct within the TestData struct

we give it a name like d so we have

type TestData struct {
    d EmbeddedTestData
}

now if we change the line from

err = inidata.Section("clientServer").MapTo(data)

to

err = inidata.Section("clientServer").MapTo(data.d)

to point to the EmbeddedTestData struct within the TestData struct and run the code again we get same output

but when we print the err from

err=inidata.Section("clientServer").MapTo(data.d)

we get

not a pointer to a struct

if we add a & to our code to point the EmbeddedTestData struct it should work

so the final code looks like this

/*
config.ini contains following example data:

[clientServer]
Port = ":1111"
WsPath = "/ws"

[courtServer]
port = ":2222"
wsPath = "/cs"
*/

package main

import (
    "fmt"
    "os"

    "github.com/go-ini/ini"
)

type TestData struct {
    d EmbeddedTestData
}

type EmbeddedTestData struct {
    Port   string
    WsPath string
}

func main() {
    // load ini-file

    inidata, err := ini.Load("config.ini")

    if err != nil {
        fmt.Printf("Fail to read file: %v", err)
        os.Exit(1)
    }
    
    data := new(TestData)
    err = inidata.Section("clientServer").MapTo(&data.d)
    fmt.Println("Content in variable 'data': ", data)
}