How do you mitigate against nil pointer dereference

[mail...@gmail.com]

Hello,

Have been struggling with mitigating against nil pointer deference and i would appreciate if anyone can help

Code 1:   Works file 

https://play.golang.org/p/lhOh9g5R9l

Code 2: Error

https://play.golang.org/p/pY4F9bK-D9

How do you validate Attr was set if its a pointer ? 

Thanks In Advance

Teety

[mhh...@gmail.com]

Hi,

some simple leads,

Use one line initialization of Person

p := &Person{Attr:&Attribute{}}

Enhance the if conditions statement

    if p.Attr != nil && p.Attr.Age < 10 {
        fmt.Println("Too Young")
    }

Use a Person constructor

func NewPerson() &Person {
    return &Person{Attr:&Attribute{}}
}

I, too, dislike that default values for struct pointer properties is nil.

[Henrik Johansson]

Expose properties as methods and do the check in the method can make the caller use easier.

--
You received this message because you are subscribed to the Google Groups "golang-nuts" group.
To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[Ian Davis]

On Fri, 13 Jan 2017, at 10:12 AM, mail...@gmail.com wrote:

Hello,

Have been struggling with mitigating against nil pointer deference and i would appreciate if anyone can help

Code 1:   Works file 

https://play.golang.org/p/lhOh9g5R9l

Code 2: Error

https://play.golang.org/p/pY4F9bK-D9

In this case you must not ignore the error returned from json.Unmarshal. If an error is returned then p will be nil.

[mail...@gmail.com]

Hello,

Thanks for the response. The Major Issue is that am getting the Data from json and its inconsistent.

Regards

Teety

[mail...@gmail.com]

Hello,

Ignoring the error does not help 

https://play.golang.org/p/a8AIcHWII6

Thank you.

[mhh...@gmail.com]

you could also implment unmarshaler interface

https://blog.gopheracademy.com/advent-2016/advanced-encoding-decoding/

[mail...@gmail.com]

Can you give example how this validation can be done via such interface ? 

[Ian Davis]

On Fri, 13 Jan 2017, at 05:17 PM, mail...@gmail.com wrote:

Hello,

Ignoring the error does not help 

https://play.golang.org/p/a8AIcHWII6

You changed your code by making your JSON valid so this is now a different problem to the one you originally asked.

You can take advantage of Go's ability to accept nil receivers to make your code more robust:

https://play.golang.org/p/dAhEqyi94U

[mhh...@gmail.com]

yeah, right, it s possible and works, but its way more complex, lets forget about this :)

This works https://play.golang.org/p/hP8Zq-LfQA

[mail...@gmail.com]

It was easier than i expected 

https://play.golang.org/p/olooozwapD

[mail...@gmail.com]

It was easier than i expected 

https://play.golang.org/p/olooozwapD

[oelm...@leadformance.com]

As a side note, I'm probably stating the obvious here, but this is only a problem because your type is `*Attribute`. Should it be `Attribute` instead, your struct would be properly initialized with its fields to their zero value.

I mention it because I'm not sure myself why, from a design point of view, it's such a common practice to make pointers out of everything by default (I like the idea that what I pass as parameter can only be altered if I explicitly allow it). 

[Henry]

This is why I prefer to expose my type through an interface and let others access the type variables through its methods. I just need to make sure the variables are properly initialized when accessed, and the rest of the code does not need to be littered with nil check.