I am going through "A Tour of Go" tutorial.
I would like to check the answer to this question:
Note: a call to
fmt.Sprint(e)inside theErrormethod will send the program into an infinite loop. You can avoid this by convertingefirst:fmt.Sprint(float64(e)). Why?
I believe this is because when the Sprint function is called, since the error is non-nil, the Error function() will again be called, and so forth, resulting in an infinite loop.
fmt.Sprint(e) will call e.Error() to convert the value e to a string. If the Error() method calls fmt.Sprint(e), then the program recurses until out of memory.
You can break the recursion by converting the e to a value without a String or Error method.
fmt.Sprintf("cannot Sqrt negative number: %f", e) works
e.Error() to do the conversion? If I try to make it implement the Stringer interface, it doesn't try to call it. What makes it seek out to the Error() method?
Sprint eventually leads to handleMethods with a verb of v. The switch inside handleMethods checks if the argument satisfies the error type before Stringer, resulting in the Error() method being called instead of String().fmt.Sprint(e) will invoke the following piece of codes from "fmt/print.go"
switch verb {
case 'v', 's', 'x', 'X', 'q':
// Is it an error or Stringer?
// The duplication in the bodies is necessary:
// setting handled and deferring catchPanic
// must happen before calling the method.
switch v := p.arg.(type) {
case error:
handled = true
defer p.catchPanic(p.arg, verb, "Error")
p.fmtString(v.Error(), verb)
return
case Stringer:
handled = true
defer p.catchPanic(p.arg, verb, "String")
p.fmtString(v.String(), verb)
return
}
}
As error case appears first, v.Error() will be executed. Endless loop here!
