int time.Duration the chicken and the egg

[joaqu...@gmail.com]

Which came first, the time assertion? or the restriction of operation to tipes?

http://play.golang.org/p/ZnT41_2OgN

I can't do SOMEVAR* time.Seconds  but i can do 12 /* or any literal number */ * time.Seconds /* Or any duration */

Does somebody knows why?...  I just want to know the reason, please, i beg you.

Cheers

JD

[Jeremy Jackins]

c := 10

is short for

var c int

c = 10

You can't multiply an int and a time.Duration, because they are different types. You can multiply a time.Duration and an untyped integer constant (like 12), because time.Duration is an integer type.

http://golang.org/ref/spec#Constant_expressions

[Benjamin Measures]

a := 15 * time.Second // this is ok

The above works because 15 is an integer literal <http://golang.org/ref/spec#Integer_literals>. This represents an integer constant <http://golang.org/ref/spec#Constants> "which may be given a type [...] implicitly when used [...] as an operand in an expression."

Thus, there is no type mismatch.

b := 15
c := b * time.Second

Here, variable b is declared to be equal to the [integer constant] 15. Variable b however, isn't an integer constant, since it is a [declared] variable. The type of b is given to be int, since it can represent the assigned integer constant.

Now, multiplying b with time.Second gives a "mismatched types" error since Go is a typed language and will not implicitly convert the type of variables.

In order to perform the operation, you'll need to convert the type of b:

c := time.Duration(b) * time.Second

"To convert an integer number of units to a Duration, multiply: [...]" <http://golang.org/pkg/time/#Duration>