support extending generic type

[cheekybits]

support extending generic type

[ThinCats]

I think it's a bit difficult to implement the same syntax as Java :), but we can use the golang style to nest the interface.

In your example, you can use existed interface defined in other packages

(The following code will work on genny df3d48a)

package genny
import (
  "bytes"
  "fmt"
)

type Something interface {
  fmt.Stringer
}

type SomethingQueue struct {
  items []Something
}

...

func (q *SomethingQueue) String() string {
  var buf bytes.Buffer
	for _, item := range q.items {
		buf.WriteString(item.String())
	}
	return buf.String()
}

It's also easy to extend other interfaces, like json.Marshaler. We can also nest with generic.Type to indicate the interface is generic

type Something interface {
  generic.Type

  json.Marshaler
  fmt.Stringer
}

We can do this because genney will replace the string identifier of the file, regardless of its actual type. In this way, we can extend more complex types while being type-safe.

I have summarized several common usages used in my toy project.

1. Type Object extends to struct (has fields)

type Object struct {
  generic.Type

  name string
  age int
}

// Now you can use it in function without compile errors
func doSomeThing(o *Object) (string, int) {
  ...
  return o.name, o.age
}

2. Type Object extends to interface (has method)

type Object interface {
  generic.Type // can be removed

  run() Object
  stop() Object
}

// use it as normal interface
func operate(o Object) {
  o.run().stop()
}

3. Mock package

// file1: demo.go
type mockPackage struct {
  // package function
  Log(...interface{}) error
  // package exported variable
  ColorRed int
  ColorGreen int
  // Not find a way to mock exported Type
}

var PackageName mockPackage

// file2: demo_template.go
// Use in another file
func normalFunc() {
  PackageName.Log("Hello", "Good")
  color := PackageName.ColorGreen
  ...
}

// use command
// geeny -in=demo_template.go -out=gen_demo.go gen "PackageName=mypkg"

Hope to be helpful :)