Integer maths in Go using constants with exponential notation

I seem to learn more about the nuances of the Go language every other day. Sometime back, I had looked at how Go untyped constants work during maths operations with typed variables.

I just found another significant part of the spec that I had previously glossed over, this one is also about untyped constants - numeric constants in Go live in an unified space with arbitrary precision and a fungible numeric type.

So, coming from a language like Python, this might not surprise us:

$ python2
Python 2.7.15 (default, Sep 18 2018, 20:16:18)

>>> i = 2000

>>> print i / 1000, type(i / 1000)
2 <type 'int'>

>>> print i / 1e3, type(i / 1e3)
2.0 <type 'float'>

This is because the exponential format (1e3) was a float, and forced the division to be a float division.

This therefore was a surprise for me when I found out that this works in Go.

i := 2000
j := 2000.0
fmt.Printf("i: %v (%T)\n", i/1e3, i/1e3)
fmt.Printf("j: %v (%T)\n", j/1e3, j/1e3)

// Prints:
//   i: 2 (int)
//   j: 2 (float64)
(Play link)

So, you can use the exponential notation for working with large numbers in Go, something I thought was a no-no earlier.

now := time.Now()
secs := now.Unix()
millis := now.UnixNano() / 1e6

fmt.Printf("Secs   since 1970: %v (%T)\n", secs, secs)
fmt.Printf("Millis since 1970: %v (%T)\n", millis, millis)

// Prints:
//    Secs   since 1970: 1538782570 (int64)
//    Millis since 1970: 1538782570453 (int64)

(Play link, note that you will find more useful values by running this on your own computer, because current time is a weird concept in the Go playground)

The Go blog post on constants has an excellent section demonstrating this:

All these constants have numeric value 1:

'b' - 'a'

Therefore, although they have different implicit default types, written as untyped constants they can be assigned to a variable of any integer type.

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