Why Does Comparing Time.Time Instances Using the == Operator Return False Even If They Represent the Same Time?

Go time comparison

You are trying to compare two time instances, but the result is not what you expect.

You have two functions GenerateWIB and GenerateUTC to change the time zone of a given time. GenerateUTC works perfectly, while GenerateWIB doesn't.

The code to compare the two times is:

<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>

The result of this comparison is always false, even though the two times are the same.

The problem is that you are using the == operator to compare two time.Time instances. The == operator compares the values of all the fields of the two structs, including the Location field.

The Location field specifies the time zone of the time instance. In your case, expect has a time zone of wib, while res has a time zone of UTC. This is why the == operator returns false.

To compare two time.Time instances correctly, you should use the Equal method. The Equal method compares the values of the wall and ext fields of the two structs, which represent the time instant. The Equal method ignores the Location field.

Here is the corrected 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.Equal(expect) {
    fmt.Printf("WIB Expect %+v, but get %+v", expect, res)
}</code>

Now, the result of the comparison is true, which is the correct result.

Note

The Equal method is more accurate than the == operator when comparing two time.Time instances. The Equal method considers only the time instant, while the == operator also considers the time zone.

In general, you should use the Equal method to compare two time.Time instances, unless you have a specific reason to use the == operator.

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