Clarification on using variables from packages

[Brendan Tracey]

I'd just like to confirm that I understand.

One can modify the value of a variable in another package

http://play.golang.org/p/f8jNirozPJ

I assume that this is a "global" change, in that all other places that there is a pointer to that variable are affected, just like normal pointers. Similarly, just like normal pointers, if you want to make sure that your variable is sandboxed, you should make a copy of the package variable, and take a reference of the copy, rather than making a reference to the package variable directly. Lastly, for this reason, it's in general a bad idea to have a "Default variable" in a package which is a pointer to a struct (even if the variable is large), because it makes it difficult to make multiple copies of that struct. Instead, a non-pointer value should be supplied, to let the user make a copy and then take a reference themselves (or a NewDefault() should be written). 

Thanks in advance.

[Andrew Gerrand]

On 3 May 2013 15:05, Brendan Tracey <tracey....@gmail.com> wrote:

I'd just like to confirm that I understand.

One can modify the value of a variable in another package

http://play.golang.org/p/f8jNirozPJ

I assume that this is a "global" change

Yes.

 

, in that all other places that there is a pointer to that variable are affected, just like normal pointers. Similarly, just like normal pointers, if you want to make sure that your variable is sandboxed, you should make a copy of the package variable, and take a reference of the copy, rather than making a reference to the package variable directly.

Yes.

 

Lastly, for this reason, it's in general a bad idea to have a "Default variable" in a package which is a pointer to a struct (even if the variable is large), because it makes it difficult to make multiple copies of that struct. Instead, a non-pointer value should be supplied, to let the user make a copy and then take a reference themselves (or a NewDefault() should be written). 

Not really. It's generally understood that package-global variables should be modified with care.

Andrew

[Brendan Tracey]

I understand, thanks for the reply