Debugging in Go


Can you spot the errors?

package main

type ThatThing interface {
    Print(...string)
}

type Thing struct {
    Name string
    token string
}

func NewThing(params ...string)(*ThatThing){
    return &Thing {
        Name: params.Name,
        token: params.Token,
    }
}

func (datThing *Thing) Print(...string) {
    fmt.Println(datThing.Name)
    fom.Println(...string)
}

func (datThing *Thing) Print2(...string) {
    fmt.Println(datThing.Name)
    fmt.Println(...string)
}

func (datThing *Thing) print(...string) {
    fmt.Println(datThing.Name)
    fmt.Println(...string)
}

t.Print("whatever")
Thing.Print2()

The provided Go code snippet contains several issues and misunderstandings. I'll explain the code's structure, its intended functionality, and the errors present.

Code Analysis

Package Declaration

package main

This line declares the main package, which is the starting point for a Go program.

Interface Definition

type ThatThing interface {
    Print(...string)
}

The ThatThing interface is defined with a single method Print that takes a variadic number of strings (...string).

Struct Definition

type Thing struct {
    Name  string
    token string
}

The Thing struct is defined with two fields: Name and token.

Constructor Function

func NewThing(params ...string) (*ThatThing) {
    return &Thing {
        Name:  params.Name,
        token: params.Token,
    }
}

The NewThing function is supposed to return a pointer to a ThatThing interface. However, there are several issues here:

The return type should be *Thing instead of *ThatThing since it returns a Thing struct.
The way it tries to access params.Name and params.Token is incorrect. params is a slice of strings, not a struct.

Method Implementations

func (datThing *Thing) Print(...string) {
    fmt.Println(datThing.Name)
    fmt.Println(...string)
}

func (datThing *Thing) Print2(...string) {
    fmt.Println(datThing.Name)
    fmt.Println(...string)
}

func (datThing *Thing) print(...string) {
    fmt.Println(datThing.Name)
    fmt.Println(...string)
}

The Print method matches the ThatThing interface. However, the use of fmt.Println(...string) is incorrect and should be fmt.Println(strings...).
The Print2 and print methods are similar, but they are not part of the ThatThing interface.
Only exported methods (starting with an uppercase letter) can be part of an interface. print with a lowercase letter cannot fulfill the ThatThing interface.

Method Calls

t.Print("whatever")
Thing.Print2()

t.Print("whatever"): This call is incorrect as t is not defined.
Thing.Print2(): This call is incorrect as Thing is a type, not an instance.

Corrected Code

Here's the corrected version of the code:

package main

import (
    "fmt"
)

type ThatThing interface {
    Print(...string)
}

type Thing struct {
    Name  string
    token string
}

func NewThing(params ...string) *Thing {
    return &Thing{
        Name:  params[0],
        token: params[1],
    }
}

func (datThing *Thing) Print(strings ...string) {
    fmt.Println(datThing.Name)
    fmt.Println(strings...)
}

func (datThing *Thing) Print2(strings ...string) {
    fmt.Println(datThing.Name)
    fmt.Println(strings...)
}

func (datThing *Thing) print(strings ...string) {
    fmt.Println(datThing.Name)
    fmt.Println(strings...)
}

func main() {
    t := NewThing("name1", "token1")
    t.Print("whatever")
    t.Print2("another", "test")
    // t.print is not accessible here as it is unexported
}

Key Points and Fixes

Correct Function Return Type: The NewThing function now correctly returns a *Thing.
Parameter Handling: The parameters are accessed correctly from the params slice.
Variadic Parameters in Print Functions: Correctly passing the variadic parameters to fmt.Println.
Instance Method Calls: Method calls are now done on an instance of Thing, not on the type itself.
Unexported Method: The print method is unexported and not used outside its package.