How to Compare Times Accurately in Go: When Should You Use `Equal()` Instead of `==`?

Time Comparison in Go

When comparing times in Go, it's crucial to consider the potential nuances associated with time zones and monotonic clock readings. The equality operator (==) compares not only the time instance but also the location and the monotonic clock reading.

To illustrate this, consider the following code:

<code class="go">expect := time.Date(2016, 12, 12, 1, 2, 3, 4, wib)
t1 := time.Date(2016, 12, 12, 1, 2, 3, 4, time.UTC)
res := GenerateWIB(t1)
if res != expect {
    fmt.Printf("WIB Expect %+v, but get %+v", expect, res)
}</code>

In this scenario, the comparison res != expect will always evaluate to true, even though the actual time represented by both res and expect is the same. This is because the inner fields of the Time struct, which represent the wall time, the extended time, the location, and the monotonic clock reading, are different for each instance.

To correctly compare times, it's recommended to use the res.Equal(expect) method, which takes into account the potential differences between inner fields and provides a more accurate comparison. The documentation for Equal method states:

"Note that the Go == operator compares not just the time instant but also the Location and the monotonic clock reading. Therefore, Time values should not be used as map or database keys without first guaranteeing that the identical Location has been set for all values, which can be achieved through use of the UTC or Local method, and that the monotonic clock reading has been stripped by setting t = t.Round(0)."

By using res.Equal(expect), you're ensuring that the comparison is based solely on the time instant and ignoring any potential differences in location or monotonic clock reading.

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