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I have a struct defined in some device.go file

type Payload struct {
    ...
    Timestamp *time.Time  `json:"timestamp,omitempty"`
    ...
}

Now I want to Initialize this struct in some other file and I'm trying this:

payload:= &device.Payload{
    ....
    Timestamp: time.Now(), // throws error
    ... //other initializations work fine
}

cannot use time.Now() (value of type time.Time) as *time.Time value in struct literal

I want to initialize the variable as the current UTC time. I'm new to golang. How do I do that?

icza
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Ayush Kumar
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2 Answers2

7

time.Now() returns a value of type time.Time, which is not *time.Time.

Note that you also cannot take the address of the return values of function calls, you can't do &time.Now() either. For details, see How to get the pointer of return value from function call?

What you may do is use a variable of type time.Time and take its address:

var t = time.Now()

payload:= &device.Payload{
    Timestamp: &t,
}

Another "popular" option is to create a helper function to return the address of a time.Time value (to which you may pass the return value of a function call directly):

func timePtr(t time.Time) *time.Time {
    return &t
}

payload:= &device.Payload{
    Timestamp: timePtr(time.Now()),
}

For details and other options, see How do I do a literal *int64 in Go?

I assume you want a pointer because you want to allow "missing time" option, which is necessary for the encoding/json package to respect a "missing time" (details: JSON omitempty With time.Time Field). Note that in other cases it may not be necessary to automatically turn to pointer: you may use the zero value of time.Time (which is a struct) to indicate the "missing time" state. To easily tell if a time.Time is its zero value, you may use Time.IsZero(). See related: Idiomatic way to represent optional time.Time in a struct

icza
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2

time.Now() returns a Time value, but your struct is looking for a pointer. Change your struct to

type Payload struct {
    ...
    Timestamp time.Time  `json:"timestamp,omitempty"`
    ...
}

from the docs (https://pkg.go.dev/time#Time):

Programs using times should typically store and pass them as values, not pointers. That is, time variables and struct fields should be of type time.Time, not *time.Time.

distrill
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