Why Does Go's `time.Now()` Output Include 'm= ' in Later Versions?

Unexpected Output from time.Time: Demystifying the "m= " String

When a Go program executes the time.Now() function, it retrieves the current timestamp. The default output of this timestamp has evolved over time, particularly with the release of Go 1.9.

The "m= " Enigma

In older versions of Go, time.Now() would output a string in the following format:

2018-07-04 12:03:07.2911671 +0530 IST

However, in Go 1.9 and later, the output has been extended to include a mysterious "m= " string:

2018-07-04 12:03:07.2911671 +0800 +08 m=+0.002000201

Why the discrepancy? This is due to the addition of monotonic clock support in Go 1.9. The "m= " string represents the monotonic time since the start of the program, expressed as a floating-point number of seconds.

Avoid Format Surprises with Format()

Instead of relying on the default output of time.Now(), it's recommended to use the Format() function to specify a custom format for the timestamp. For example:

import (
    "fmt"
    "time"
)

func main() {
    t := time.Now()
    fmt.Println(t.Format("2006-01-02 15:04:05.000000"))
}

This will output the timestamp in a consistent format regardless of the Go version:

2018-07-04 12:03:07.2911671

By using Format(), you can ensure that your programs always output timestamps in the format that you expect.

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