golang reusing methods of struct

Question

I am learning go and was looking at a simple go example web app: https://github.com/campoy/todo/blob/master/task/task.go

Having struct:

    type Task struct {
        ID    int64  // Unique identifier
        Title string // Description
        Done  bool   // Is this task done?
    }

and

    // TaskManager manages a list of tasks in memory.
    type TaskManager struct {
        tasks  []*Task
        lastID int64
    }

There are methods on the TaskManager func (m *TaskManager) Save(task *Task) error ... func (m *TaskManager) All() []*Task...

I am wondering how to generalize TaskManager into Manager, so it would have these same methods (namely: save, all, find) so it can be used on different structs, for example Users, which would all have ID field.

I assume constructing an array of general type doesn't fit because there is an ID in 'save' and 'find' methods

Donald Duck is with Ukraine · Accepted Answer · 2018-07-13 01:15:36Z

3

Go doesn't have generics (for now, at least), but you still can perform what you want (not 100%) by using an interface.

type Manager interface {
  Save(interface{}) error
  All() ([]interface{}, error)
}

Of course, it doesn't come for free and you need to do some error handling in your TaskManager to implement the interface, example:

func (m *TaskManager) Save(t interface) error {
  task, ok := t.(Task) // type assertion
  if !ok {
    // return error invalid input type
  }
  // do the rest as normal...
}

:Example for comment

type Entry interface {
  SetID(int64)
  GetID()int64
}

type Task struct {...}

func (t *Task) SetID(id int64) {...}
func (t *Task) GetID() {...}

func (m *TaskManager) Save(e Entry) error {...}

More info on interfaces: * http://golang.org/ref/spec#Interface_types
* http://golang.org/doc/effective_go.html#interfaces_and_types
*http://golangtutorials.blogspot.com/2011/06/interfaces-in-go.html

edited Jul 13, 2018 at 1:15

Donald Duck is with Ukraine

9,00223 gold badges81 silver badges106 bronze badges

answered Apr 1, 2014 at 2:50

nvcnvn

5,2238 gold badges54 silver badges78 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

user3483228 Over a year ago

Thanks for your writeup. But, that is still not clear to me. The part, t.(Task) could be any struct with Id, for example 't.(User)' or 't.(Video)'. It looks to me as if it's implementing "Save" on Task only, while I'd like Save on any of the structs.

nvcnvn Over a year ago

The point is you will have TaskManager for Task and UserManager for User. Both TaskManager and UserManager are Manager. There is no simple (see package reflection) way to tell you if a struct have the Id field or not.

nvcnvn Over a year ago

Any way you can define an Entry interface with SetID, GetID and let User/Task implement it. Then Manager with Save(Entry) etc...

Evan · Accepted Answer · 2014-04-01 02:49:14Z

0

You'll probably want to write an interface for structures that have an ID, then generalize your Manager to operate on elements of that interface instead of elements of a specific struct.

answered Apr 1, 2014 at 2:49

Evan

6,5731 gold badge31 silver badges30 bronze badges

Collectives™ on Stack Overflow

golang reusing methods of struct

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related