Copy struct with private field

[Archos]

Any way to copy struct with private fields?

I get a command to run `cmd` and since it could be run several times,
before of call cmd.Wait(), then I would want copy it

// * * *

cmd := exec.Command(name, arg...)

func copy(cmd *exec.Cmd) *exec.Cmd {
cmd_ := *cmd
return &cmd_
}

// * * *

but I get an error:

implicit assignment of unexported field 'err' of exec.Cmd in assignment

[Jeremy Wall]

Wouldn't dereferencing the pointer and assigning to a variable
effectively copy it? I *think* it would but I'm actually not sure so
I'm asking the wider list.

[Jan Mercl]

On Wednesday, November 9, 2011 5:18:58 PM UTC+1, Archos wrote:

Any way to copy struct with private fields?

No. Intentionally not allowed. There may be some state in it which must be initialized and/or not reused and/or unique to its instance etc. Knowing/looking at the (imported package) sources doesn't help as the struct type private internals (and their semantics) can change at any time in the future - without breaking the public/exported API.

Specs: http://golang.org/doc/go_spec.html#Assignability

"If T is a struct type with non-exported fields, the assignment must be in the same package in which T is declared, or x must be the receiver of a method call. In other words, a struct value can be assigned to a struct variable only if every field of the struct may be legally assigned individually by the program, or if the assignment is initializing the receiver of a method of the struct type."