Error question: "cannot use nil as type string in return argument"

[Travis Reeder]

Forgive my noobness, but why can't I return nil for string return?

I get "cannot use nil as type string in return argument" with the following:

func nextLine(src *bufio.Reader) (string, os.Error) {

line, isPrefix, err := src.ReadLine()

// discard the rest of long lines

for isPrefix {

_, isPrefix, err = src.ReadLine()

}

if line == nil {

return nil, nil

}

if err != nil {

return nil, err

}

line_s := string(line)

return line_s, nil

}

[andrey mirtchovski]

use "" for string nils.

[Jan Mercl]

On Monday, June 13, 2011 11:57:48 PM UTC+2, Travis Reeder wrote:

Forgive my noobness, but why can't I return nil for string return?

http://golang.org/doc/go_spec.html#Assignability

A value x is assignable to a variable of type T ("x is assignable to T") in any of these cases:

...

x is the predeclared identifier nil and T is a pointer, function, slice, map, channel, or interface type.

... 

The specs clause doesn't mention string, so "stringvar = nil" is (ATM) out of specs.