[go-nuts] slice of unaddressable value

[Runix]

Hi, why in the first slice get the error, the second is not?

var a = ([...]interface{}{})[:]
fmt.Println(a)

var b = [...]interface{}{}
fmt.Println(b[:])

http://play.golang.org/p/uxJjvNLGI5

[Vasko Zdravevski]

Hi Runix,

The answer to your question seems to be in the spec here:
http://golang.org/ref/spec#Slice_expressions

If the sliced operand is an array, it must be addressable
<http://golang.org/ref/spec#Address_operators> and the result of the slice
operation is a slice with the same element type as the array.


http://golang.org/ref/spec#Address_operators

Just needed to add an "&" to get the address of the created array. Here is
the 1 character change to your code that makes it work:
http://play.golang.org/p/M4h1dzOl7f

Hope this helps,
Vasko.

Post by Runix
Hi, why in the first slice get the error, the second is not?
var a = ([...]interface{}{})[:]
fmt.Println(a)
var b = [...]interface{}{}
fmt.Println(b[:])
http://play.golang.org/p/uxJjvNLGI5

[Runix]

What about

As an exception to the addressability requirement, x may also be a
(possibly parenthesized) composite literal.

CompositeLit = LiteralType LiteralValue .
LiteralType = "[" "..." "]" ElementType
LiteralValue = "{" [ ElementList [ "," ] ] "}" .

Post by Vasko Zdravevski
Hi Runix,
http://golang.org/ref/spec#Slice_expressions
If the sliced operand is an array, it must be addressable
<http://golang.org/ref/spec#Address_operators> and the result of the
slice operation is a slice with the same element type as the array.
http://golang.org/ref/spec#Address_operators
Just needed to add an "&" to get the address of the created array. Here is
http://play.golang.org/p/M4h1dzOl7f
Hope this helps,
Vasko.

Post by Runix
Hi, why in the first slice get the error, the second is not?
var a = ([...]interface{}{})[:]
fmt.Println(a)
var b = [...]interface{}{}
fmt.Println(b[:])
http://play.golang.org/p/uxJjvNLGI5

[Brad Fitzpatrick]

It needs to live somewhere in memory to take its address.

A variable is that place in memory.

Post by Runix
What about
As an exception to the addressability requirement, x may also be a
(possibly parenthesized) composite literal.
CompositeLit = LiteralType LiteralValue .
LiteralType = "[" "..." "]" ElementType
LiteralValue = "{" [ ElementList [ "," ] ] "}" .
среЎа, 3 ОюМя 2015 г., 23:59:53 UTC+5 пПльзПватель Vasko Zdravevski

Post by Vasko Zdravevski
Hi Runix,
http://golang.org/ref/spec#Slice_expressions
If the sliced operand is an array, it must be addressable
<http://golang.org/ref/spec#Address_operators> and the result of the
slice operation is a slice with the same element type as the array.
http://golang.org/ref/spec#Address_operators
Just needed to add an "&" to get the address of the created array. Here
http://play.golang.org/p/M4h1dzOl7f
Hope this helps,
Vasko.

Post by Runix
Hi, why in the first slice get the error, the second is not?
var a = ([...]interface{}{})[:]
fmt.Println(a)
var b = [...]interface{}{}
fmt.Println(b[:])
http://play.golang.org/p/uxJjvNLGI5

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[Ian Lance Taylor]

Post by Runix
What about
As an exception to the addressability requirement, x may also be a (possibly
parenthesized) composite literal.
CompositeLit = LiteralType LiteralValue .
LiteralType = "[" "..." "]" ElementType
LiteralValue = "{" [ ElementList [ "," ] ] "}" .

That appears in the section on the address operator. It is what
permits the '&' in &S{f:v}. It's not a general description of what is
addressable.

Ian

[Vasko Zdravevski]

Hi Runix,

I trust you have a need for this, but why do you need to first create an
array literal using "[...]" and then turn that into a slice with the slice
expression? Why not just start off with a slice?

http://play.golang.org/p/8RQwhkVN6p

Post by Runix
Hi, why in the first slice get the error, the second is not?
var a = ([...]interface{}{})[:]
fmt.Println(a)
var b = [...]interface{}{}
fmt.Println(b[:])
http://play.golang.org/p/uxJjvNLGI5

[Runix]

Thank you all for answers