Slices

So to solve the problem we had at hand in previous chapter, Slices are Go's response to have array of dynamic length. But there is gotcha, one need to define length of slice at the time of declaration, but more data of same type could be appended to slices in future. For example

slice := make([]string, 3)    // make is similar to new
fmt.Println("Empty:", slice)

So what we have done? We have defined a slice of type string having length 3. We can dynamically assign values to slices similar to array. In example above make is similar to new keyword. Like

slice[0] = "apple",
slice[1] = "orange"
slice[2] = "banana"

To get the length of slices, we have similar len function as array

len(slice) //=> 3

Go provides a special method called append for slices. this method actally creates a new slice with new lenght, assigning old and new element to it and returning a new slice. That returned slice should be saved in a variable to have access to it.

slice := make([]string, 3)    // make is similar to new
fmt.Println("Empty:", slice)
slice[0] = "apple"
slice[1] = "orange"
slice[2] = "banana"
slice = append(slice, "peach")
slice = append(slice, "mango", "strawberry")
fmt.Println("Append:", slice)

Unlike Array, in Go slices has copy utility, that allows copying over slices. To copy our variable slice to copied variable, one can do like following

copied := make([]string, len(slice))
copy(copied, slice)

In first line we make another slice of length of slice variable and then use copy function to copy over content of slice variable to copied variable

In addition to all those utility methods, Go provide a slice operator for slices, syntax for that looks like [from:to] where from is index number of slice to start from and go upto to index but excluding to . To illustrate, we would use our previous example

sub = slice[2:5]
fmt.Println("sliced sub: ", sub)
// => sliced sub: [banana peach mango]

So, now its more clear. This has sliced from index 2 to 4 (excluding index 5). Similarly

// => This can be read as [0:5]
sub = slice[:5]
// => [apple orange banana peach]

Go also allows special syntaxfrom start index to length of slice

// => This would copy over all elements fro index 4 to end
slice[4:]
// => [apple orange banana peach]