I found this in some code:
h := s.Hash(tx)
sig, err := crypto.Sign(h[:], prv)
What does [:] mean ? If this is the full slice of the array, why not to pass the array itself? What kind of coding style is this, I wonder...
In go, Arrays and Slices are slightly different and cannot be used interchangeably; however, you can make a slice from an array easily using the [:] operator.
This article explains in detail - Go Slices: Usage and Internals.
See also the Slice Expressions section of The Go Programming Language Specification.
In a nutshell, the [:] operator allows you to create a slice from an array, optionally using start and end bounds. For example:
a := [3]int{1, 2, 3, 4} // "a" has type [4]int (array of 4 ints)
x := a[:] // "x" has type []int (slice of ints) and length 4
y := a[:2] // "y" has type []int, length 2, values {1, 2}
z := a[2:] // "z" has type []int, length 2, values {3, 4}
m := a[1:3] // "m" has type []int, length 2, values {2, 3}
Presumably the reason for this distinction is for an extra measure of type safety. That is, length is a formal part of an array type (e.g. [4]int is an array of four ints and a different size is a different type) whereas slices can have any length, including zero. So if you want the safety of a known-length sequence then use an Array, otherwise use a Slice for convenience.