Admin: Created page with "{{Main|Go/Arrays}} The Go blog (this post: https://blog.golang.org/slices) gets lost on a (rather stupid and uninformative) topic, which is, array slices. To insert an elem..."

2018-12-13T00:07:26Z

Created page with "{{Main|Go/Arrays}} The Go blog (this post: https://blog.golang.org/slices) gets lost on a (rather stupid and uninformative) topic, which is, array slices. To insert an elem..."

New page

{{Main|Go/Arrays}}

The Go blog (this post: https://blog.golang.org/slices) gets lost on a (rather stupid and uninformative) topic, which is, array slices.

To insert an element into a slice of an array, we can do the following (NOTE: This is NOT the same as inserting an element into an array):

* Extend the slice window by 1
* Shift the upper part of the slice's underlying array data up by 1, using the copy function
** Copying FROM the variable slice, starting at index and running to the end
** Copying TO the variable slice, starting at index + 1 and running to the end
* Return the new slice

This operation WILL NOT affect the underlying data.

Here is the Insert function, plus a main method that calls it:

<pre>
// Insert inserts the value into the slice at the specified index,
// which must be in range.
// The slice must have room for the new element.
func Insert(slice []int, index, value int) []int {

// Grow the slice by one element.
slice = slice[0 : len(slice)+1]

// Use copy to move the upper part of the slice out of the way and open a hole.
copy(slice[index+1:], slice[index:])

// Store the new value.
slice[index] = value

// Return the result.
return slice
}
</pre>

Aside from the stupidity of the example (not making clear why you would want to insert something into a slice of an array but not the array itself; not making clear the underlying data or the memory/reference model in Go).

Basically this whole blog post is a hot mess.

The confusion here is, the text seems to contradict the behavior of this function.

* The text describing this example insists we are passing a copy of the slice, but that copy should refer to the same data underneath.
* However, when we expand the length of the slice, and shift everything over, and insert a value, this doesn't affect the data underneath.

The answer: we aren't creating a slice by saying <code>slice = orig[5:10]</code>, we are creating a slice by saying <code>slice = make([]int, 4, 8)</code> and then <code>copy(slice,orig)</code>.

When we call make, we're basically allocating an underlying array for a slice.

[https://stackoverflow.com/questions/9320862/why-would-i-make-or-new Related question on Stack Overflow]

{{GoFlag}}

Go/Arrays/Array Slice Insertion - Revision history

Admin: Created page with "{{Main|Go/Arrays}} The Go blog (this post: https://blog.golang.org/slices) gets lost on a (rather stupid and uninformative) topic, which is, array slices. To insert an elem..."