allow direct conversion between string and named []byte, []rune

The allowed conversions before and after are:
        type Tstring string
        type Tbyte []byte
        type Trune []rune

        string <-> string  // ok
        string <-> []byte  // ok
        string <-> []rune // ok
        string <-> Tstring // ok
        string <-> Tbyte // was illegal, now ok
        string <-> Trune // was illegal, now ok

        Tstring <-> string  // ok
        Tstring <-> []byte  // ok
        Tstring <-> []rune // ok
        Tstring <-> Tstring // ok
        Tstring <-> Tbyte // was illegal, now ok
        Tstring <-> Trune // was illegal, now ok

Update spec, compiler, tests.  Use in a few packages.

We agreed on this a few months ago but never implemented it.

Fixes issue 1707.

R=golang-dev, gri, r
CC=golang-dev
http://codereview.appspot.com/5421057

1 files changed, 3 insertions, 3 deletions

diff --git a/test/convlit.go b/test/convlit.go
index 2e3b15bda..1e82d1f2f 100644
--- a/test/convlit.go
+++ b/test/convlit.go
@@ -54,12 +54,12 @@ var _ = []byte(ss)
 var _ []rune = ss // ERROR "cannot use|incompatible|invalid"
 var _ []byte = ss // ERROR "cannot use|incompatible|invalid"
 
-// named slice is not
+// named slice is now ok
 type Trune []rune
 type Tbyte []byte
 
-var _ = Trune("abc") // ERROR "convert|incompatible|invalid"
-var _ = Tbyte("abc") // ERROR "convert|incompatible|invalid"
+var _ = Trune("abc") // ok
+var _ = Tbyte("abc") // ok
 
 // implicit is still not
 var _ Trune = "abc" // ERROR "cannot use|incompatible|invalid"