Is there a difference between a slice and a full reslice of it?
given a slice s:= make([]byte, 4, 4),
is there a difference between copy(s[:], "data") and copy(s, "data")?
Is there a case where these two lines will output different results?
CodePudding user response：
Slices in Go have 3 properties:
- The underlying array
- The length of the slice
- The capacity of the slice
s and s[:] will be identical with respect to all the above properties.
Go doesn't actually define an == operation for slices, but s and s[:] are equal in the sense that all measurable properties are the same.
The copy function is only concerned with the first 2 properties, which are identical between s and s[:].
CodePudding user response：
In Go, a slice is a data structure that represents a sequence of elements. It is essentially a reference to an underlying array, and it allows you to work with a contiguous subset of the array's elements.
When you create a slice, you specify the length and capacity of the slice, which determine how many elements the slice can hold and how many elements are currently stored in the slice, respectively. The length is the number of elements currently stored in the slice, while the capacity is the maximum number of elements the slice can hold without needing to allocate a new underlying array.
A reslice of a slice is a new slice that is created from an existing slice. It allows you to create a new slice that shares the same underlying array as the original slice, but with a different length and/or capacity.
In the case of a full reslice, the new slice will have the same length and capacity as the original slice. This means that the new slice will be able to hold the same number of elements as the original slice, and it will have the same number of elements currently stored in it.
In the case of the example you provided, there is a difference between the two lines of code you provided. The first line of code, copy(s[:], "data"), creates a full reslice of the slice s and then copies the string "data" into the new slice. The second line of code, copy(s, "data"), copies the string "data" into the original slice s, overwriting any existing data that was stored in the slice.
There are cases where these two lines of code will produce different results. For example, if the original slice s contains more elements than the string "data", the first line of code will truncate the slice to have the same length as the string, while the second line of code will leave the extra elements in the slice unchanged.