Cannot take the address of the result of append

[gopherbot]

by yiyu.jgl:

What steps will reproduce the problem?

// Example:
package main

func main() {
    _ = &append([]int{1, 2}, 3)[:]
}

What is the expected output?

A successful compile.

What do you see instead?

prog.go:4: cannot take the address of append(slice literal, 3)[:]

Which compiler are you using (5g, 6g, 8g, gccgo)?
Which operating system are you using?
Which revision are you using?  (hg identify)

Go Playground at golang.org

Please provide any additional information below.

In my opinion, it should be possible to directly take the address of append, as in
&append(a, b), but I'm not sure the spec allows it. However, it specifically says
the address operator can be used with an slice indexing operation, so I think it should
work for &append(a, b)[:]

[peterGo]

Comment 1:

"The function append appends zero or more values x to a slice s and returns the
resulting slice, with the same type as s."
Appending to and copying slices, , The Go Programming Language Specification.
http://golang.org/doc/go_spec.html#Appending_and_copying_slices
Therefore, we can simply consider a slice s.
package main
func main() {
    s := []int{1, 2}
    _ = &s
    _ = &s[0]
    _ = s[0:len(s)]
    // cannot take the address of s[0:len(s)]
    _ = &s[0:len(s)]
    // cannot assign to s[0:len(s)]
    s[0:len(s)] = s[0:len(s)]
}
"The address-of operator & generates the address of its operand, which must be
addressable, that is, either a variable, pointer indirection, or slice indexing
operation; or a field selector of an addressable struct operand; or an array indexing
operation of an addressable array."
Address operators, The Go Programming Language Specification.
http://golang.org/doc/go_spec.html#Address_operators
"A primary expression of the form a[x] denotes the element of the array, slice, string
or map a indexed by x."
Indexes, The Go Programming Language Specification
http://golang.org/doc/go_spec.html#Indexes
"For a string, array, or slice a, the primary expression a[low : high] constructs a
substring or slice. The index expressions low and high select which elements appear in
the result. The result has indexes starting at 0 and length equal to high - low."
Slices, The Go Programming Language Specification.
http://golang.org/doc/go_spec.html#Slices
"Each left-hand side operand must be addressable, a map index expression, or the blank
identifier."
Assignments, , The Go Programming Language Specification.
http://golang.org/doc/go_spec.html#Assignments
The variable s is a slice of int. You can take the address of the variable s: &s. You
can take the address of the result of a slice indexing operation, an indexed element of
the variable s: &s[0]. You can assign the result of a slicing operation on the variable
s to a variable of the same type: _ = s[0:len(s)]. You can't take the address of the
result of a slicing operation on the variable s: &s[0:len(s)]. It's not addressable;
it's not the same as a slice indexing operation. You can't assign to a slicing operation
on the variable s: s[0:len(s)] = s[0:len(s)]. It's not addressable.

[gopherbot]

Comment 2 by yiyu.jgl:

You are right. The issue should be closed, sorry.
I was incorrectly considering that slicing was an slice indexing operation, but there is
no need to copy the spec here.

[robpike]

Comment 3:

Status changed to Invalid.