[wishlist] 'Safe Navigation Operator'.

[Constantin Kulikov]

http://groovy.codehaus.org/Operators#Operators-SafeNavigationOperator%28?.%29

and here(7. Monadic null checking): http://damieng.com/blog/2013/12/09/probable-c-6-0-features-illustrated

before:
var num int = -1
if nil != point {
   num = points.Get_number_of_points()
   points.Void_method()
}

after:
num := points?.Get_number_of_points() ?? -1
points?.Void_method()

[Jonathan Amsterdam]

Go methods on pointers can have null receivers.

type Point struct { x, y int }

func (p *Point) Translate(dx, dy int) {

if p != nil {

p.x += dx

p.y += dy

}

}

func main() {

var p *Point

p.Translate(1, 2) // does not panic

        // ...

[Constantin Kulikov]

Okay.jpg

Then it may be helpful for null interfaces.

example:

type IPoint interface {
    Translate(dx,dy int)
}

var something IPoint = nil // 'untyped' nil

something?.Translate(1,2) // don't panic

something.Translate(1,2) // panic!

OR:

func megafunc_on_point(point IPoint) {
  point?.Translate(1,1)
  return
}


среда, 11 декабря 2013 г., 1:53:25 UTC+4 пользователь Jonathan Amsterdam написал:

[Volker Dobler]

Am Dienstag, 10. Dezember 2013 23:21:49 UTC+1 schrieb Constantin Kulikov:

...

something?.Translate(1,2) // don't panic

...

Fine, no panic. But what *does* happen? Just a no-op? Does that help?

V. 

[Constantin Kulikov]

For this case no panic, no-op.

When method intended to return value:

ret := something?.M_with_return_

value() ?? default_value

[Dave Cheney]

Dear OP,

Please take the time to learn Go throughly before proposing a language change. 

I am confident that you will find that your proposal is unwarranted because the use of nil as a *VALID* return value is dramatically less that in other languages such as Java and C#.

The remaining cases are programming error and should be fixed by the author, not worked around with a new syntax. 

Cheers

Dave

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[luz...@gmail.com]

I know this "safe navigation operator" from Groovy. It can get a bit annoying: people tend to use it everywhere instead of ".", "just to be on the safe side". It's only really useful if you have long "train wreck" chains like "A.B.C.D.E.F", where each component can be nil. The better design is to avoid "train wrecks" (Law of Demeter) and excessive use of nil pointers. Initialize pointers before usage, use more value types. Also, strings in Go can't be nil and nil slices are valid empty slices.

Go doesn't even support the ternary "?:" operator, because it hides control flow branches inside a single line, and each "?." is a hidden "if" as well.