If I do this:
func main() {
foo := 1
go func() {
fmt.Println(foo)
}()
}
is referencing foo inside that func wrong?
It is fine, only in changing context needs some attention(in case of local pointer variables):
package main
import (
"errors"
"fmt"
)
func test() {
defer func() { fmt.Println(1) }()
defer func() { fmt.Println(2) }()
defer func() { fmt.Println(3) }()
}
func main() {
test()
err := errors.New("error 1")
defer func() { fmt.Println(err) }()
err = errors.New("error 2")
}
and also see:
https://www.goinggo.net/2014/06/pitfalls-with-closures-in-go.html
Its not "wrong" but its not good practice.
Let me expand a bit.
lets say I do this:
func main() {
foo := 1
go func() {
foo = 2
fmt.Println(foo)
}()
}
In the case above, 2 will be printed. Now imagine there's 20+ lines between foo := 1 and foo=2. There's a high chance you would get behaviour you don't expect and you'll have a hard time tracking since the change isn't explicit. Instead you should do:
func main() {
foo := 1
go func(bar int) {
bar = 2
fmt.Println(bar)
}(foo)
}
Now the code is explicitly changing the value of bar (which is equivalent to foo) within func(int bar). To change the value of foo in main, you do:
func main() {
foo := 1
go func(bar *int) {
*bar = 2
fmt.Println(*bar)
}(&foo)
}