CODEWITHSUNDEEP
go
Datsik
Datsik

Reputation: 14824

What exactly is (nil) doing in this context []string(nil)

I was looking at the Slice Tricks: https://github.com/golang/go/wiki/SliceTricks

and I noticed in their copy example they have []T(nil)

I haven't seen (nil) like this before and I can't find any documentation on using it or what exactly it accomplishes (I know it's self explanatory but I want to know how it acts the same as make or []string{}

the only reference I can find by googling "golang (nil) slice" is

Since the zero value of a slice (nil) acts like a zero-length slice, you can declare a slice variable and then append to it in a loop:

But it doesn't say where it can be used or exactly what it accomplishes, like can I use this with structs or whatever I want?

e.g.:

package main

import "log"

func main() {
    str := []string{"Hello", "Bye", "Good Day", "????????"}
    cop := append([]string(nil), str...)    

    log.Println(str)
    log.Println(cop)
}

I'm strictly only curious about how (nil) operates, and what it can operate on.

Like does 

[]string(nil)

Operate the same as

[]string{}

or what is the difference here

Upvotes: 11

Views: 2614

Answers (2)

Mr_Pink
Mr_Pink

Reputation: 109442

This is a type conversion, converting a nil to a slice.

These are equivalent 

var t []string
t := []string(nil)

In both cases, t is of type []string, and t == nil

Upvotes: 13

nerdy900
nerdy900

Reputation: 348

list := []string(nil) // list is an empty slice of strings

func append(slice []Type, elems ...Type) []Type

function takes a slice of strings and a variable length list of strings, and returns a slice where the list of strings is appended to the end.

so:

cop := append([]string(nil), str...)

will create an empty slice of strings and append the strings in "str" and return the result.

This the result slice is a copy, because it has all of the same values in the same order.

Upvotes: 1

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