Is there idiomatic scoped semantics in golang? - go

Question

I wonder if there is any idiomatic way to represent scoped semantics. By scoped I mean things like:
scoped mutex (oneliner instead of explicit Lock + deffered Unlock),
logging function (or any code block) entrance and exit,
measuring execution time.
Example code for first two bullets:
package main
import "log"
import "sync"
func Scoped(m *sync.Mutex) func() {
m.Lock()
return func() {
m.Unlock()
}
}
func Log(what string) func() {
log.Println(what, "started")
return func() {
log.Println(what, "done")
}
}
func main() {
defer Log("testing")()
m := &sync.Mutex{} // obviously mutex should be from other source in real life
defer Scoped(m)()
// use m
}
https://play.golang.org/p/33j-GrBWSq
Basically we need to make one function call just now (eg mutex lock), and one call should be postponed to defer (eg mutex unlock). I propose just returning unnamed function here, but it can be easily named (return struct with function field).
There is only one problem: user can forget to 'call' result of first call.
This code is (can be) idiomatic?

Answer 1

Take anonymous function as a scope:
func() {
Entrance()
defer Exit()
// anything you want to do in this scope
}()

Answer 2

Your proposed solution is already nice. You return a value of func type which you also have to call at the end of the defer.
You can avoid that (returning a func value), but there have to be 2 function calls, one that logs the start event and another one that logs the end event.
The alternative is to make a function call which produces the parameter value of the function that is deferred (rather than returning a function) which is evaluated with the defer statement, and this way it still can remain one line.
You can also try it on the Go Playground:
func start(s string) string {
fmt.Println("Started", s)
return s
}
func end(name string) {
fmt.Println("Ended", name)
}
func main() {
defer end(start("main"))
fmt.Println("Doing main's work...")
}
Output:
Started main
Doing main's work...
Ended main

Answer 3

I do not believe there is an idiomatic way to do this. I'm not sure why you'd want to either, is it really so bad to write
m.Lock()
defer m.Unlock()
?

Answer 4

I think question isn't relevant to Go idiomaticity, Seems it's generally better to reason about code when function behave identically either call. To keep state I'd better make an object and define function as method on that object. Means something like
type message string
func (foo message) Log(bar string){
if bar==nil{doSomethingSpecial()}
switch foo{
case something: doSomething()
...
case nil: doSomethingInitial()
default: doDefault()
}
log.Println(bar, "started")
foo=bar
}