String and GString do not commute under plus()

this is not a critical bug, so I reduce the priority

This issue is not there anymore. Checked on all 3 branches (1.5, 1.6, 1.7).

So let's close it

Alexander, could you try trunk and the 1.6 branch?

With both tunk and GROOVY_1_6_X, rev. 14993, the two asserts

assert "${1}" + "2" instanceof GString
assert "1" + "${2}" instanceof String

work. So GString and String do not commute under plus.

I wonder if I'm doing something wrong...

ok, I see... the actual problem is not that the test should pass, but that it does pass... You say that if String+GString gives T, then GString+String should give T as well. Ok, what should T be and why?

... and why?

The current behavious can lead to surprising errors. E.g. when object identity comes into play as shown here

def u = []
def v = 'foo'

u << "${v}" + "bar"
u << "bar" + "${v}"

assert u.contains("foobar") == false
assert u.contains("barfoo") == true

or with lazy closure evaluation as shown here

int i
def g
def s
def t

Closure c = {-> i}
g = "$c"

i = 1
s = g + "--"
i = 2
t = g + "--"
assert s == t

i = 1
s = "--" + g
i = 2
t = "--" + g
assert s != t

what should T be

That depends on the language spec

For the sake of simplicity, for implementation and user, I would tend to T = String. This would be probably also be more compatible to other operations such as leftShift.