From ac6ebfdea9e52a82bb55f7eb28c79619e2ffba10 Mon Sep 17 00:00:00 2001
From: Russ Cox <rsc@golang.org>
Date: Mon, 6 Apr 2009 21:28:04 -0700
Subject: [PATCH] add method Value() Value to InterfaceValue. use Value() in
 print to print underlying value from interface.

before:
	package main
	import "fmt"
	func main() {
		x := []interface{} {1, "hello", 2.5};
		fmt.Println(x[0], x[1], x[2], x);
	}

	1 hello 2.5 [<non-nil interface> <non-nil interface> <non-nil interface>]

after:
	1 hello 2.5 [1 hello 2.5]

R=r
DELTA=44  (22 added, 16 deleted, 6 changed)
OCL=27139
CL=27141
---
 src/lib/fmt/fmt_test.go     | 22 ++++------------------
 src/lib/fmt/print.go        |  7 +++----
 src/lib/reflect/all_test.go | 10 ++++++++++
 src/lib/reflect/value.go    | 11 +++++++++++
 4 files changed, 28 insertions(+), 22 deletions(-)

diff --git a/src/lib/fmt/fmt_test.go b/src/lib/fmt/fmt_test.go
index 34acab08be..e4158624b0 100644
--- a/src/lib/fmt/fmt_test.go
+++ b/src/lib/fmt/fmt_test.go
@@ -29,7 +29,7 @@ type fmtTest struct {
 const b32 uint32 = 1<<32 - 1
 const b64 uint64 = 1<<64 - 1
 var array = []int{1, 2, 3, 4, 5}
-
+var iarray = []interface{}{1, "hello", 2.5, nil}
 
 var fmttests = []fmtTest{
 	// basic string
@@ -80,10 +80,10 @@ var fmttests = []fmtTest{
 	fmtTest{ "% d",		-12345,	"-12345" },
 
 	// arrays
-	// TODO: when arrays work in interfaces, enable this line
-	// and delete the TestArrayPrinter routine below
-	// fmtTest{ "%v",		array,			"[1 2 3 4 5]" },
+	fmtTest{ "%v",		array,			"[1 2 3 4 5]" },
+	fmtTest{ "%v",		iarray,			"[1 hello 2.5 <nil>]" },
 	fmtTest{ "%v",		&array,			"&[1 2 3 4 5]" },
+	fmtTest{ "%v",		&iarray,			"&[1 hello 2.5 <nil>]" },
 
 	// old test/fmt_test.go
 	fmtTest{ "%d",		1234,			"1234" },
@@ -240,17 +240,3 @@ func TestStructPrinter(t *testing.T) {
 		}
 	}
 }
-
-func TestArrayPrinter(t *testing.T) {
-	a := []int{1, 2, 3, 4, 5};
-	want := "[1 2 3 4 5]";
-	out := fmt.Sprintf("%v", a);
-	if out != want {
-		t.Errorf("Sprintf(%%v, array) = %q, want %q", out, want);
-	}
-	want = "&" + want;
-	out = fmt.Sprintf("%v", &a);
-	if out != want {
-		t.Errorf("Sprintf(%%v, &array) = %q, want %q", out, want);
-	}
-}
diff --git a/src/lib/fmt/print.go b/src/lib/fmt/print.go
index ca5bec9341..5fd230f2ce 100644
--- a/src/lib/fmt/print.go
+++ b/src/lib/fmt/print.go
@@ -451,12 +451,11 @@ func (p *pp) printField(field reflect.Value) (was_string bool) {
 		}
 		p.add('}');
 	case reflect.InterfaceKind:
-		inter := field.(reflect.InterfaceValue).Get();
-		if inter == nil {
+		value := field.(reflect.InterfaceValue).Value();
+		if value == nil {
 			s = "<nil>"
 		} else {
-			// should never happen since a non-nil interface always has a type
-			s = "<non-nil interface>";
+			return p.printField(value);
 		}
 	default:
 		s = "?" + field.Type().String() + "?";
diff --git a/src/lib/reflect/all_test.go b/src/lib/reflect/all_test.go
index 166b20702f..e3f6b9b506 100644
--- a/src/lib/reflect/all_test.go
+++ b/src/lib/reflect/all_test.go
@@ -301,6 +301,16 @@ func TestInterfaceGet(t *testing.T) {
 	assert(v3.Type().String(), "float");
 }
 
+func TestInterfaceValue(t *testing.T) {
+	var inter struct { e interface{ } };
+	inter.e = 123.456;
+	v1 := reflect.NewValue(&inter);
+	v2 := v1.(reflect.PtrValue).Sub().(reflect.StructValue).Field(0);
+	assert(v2.Type().String(), "interface { }");
+	v3 := v2.(reflect.InterfaceValue).Value();
+	assert(v3.Type().String(), "float");
+}
+
 func TestCopyArray(t *testing.T) {
 	a := []int{ 1, 2, 3, 4, 10, 9, 8, 7 };
 	b := []int{ 11, 22, 33, 44, 1010, 99, 88, 77, 66, 55, 44 };
diff --git a/src/lib/reflect/value.go b/src/lib/reflect/value.go
index 7bd6f3b153..ad0cd46556 100644
--- a/src/lib/reflect/value.go
+++ b/src/lib/reflect/value.go
@@ -34,6 +34,8 @@ type Value interface {
 	Interface()	interface {};
 }
 
+func NewValue(e interface{}) Value;
+
 // commonValue fields and functionality for all values
 
 type commonValue struct {
@@ -744,6 +746,7 @@ func structCreator(typ Type, addr Addr) Value {
 type InterfaceValue interface {
 	Value;
 	Get()	interface {};	// Get the underlying interface{} value.
+	Value() Value;
 }
 
 type interfaceValueStruct struct {
@@ -754,6 +757,14 @@ func (v *interfaceValueStruct) Get() interface{} {
 	return *(*interface{})(v.addr)
 }
 
+func (v *interfaceValueStruct) Value() Value {
+	i := v.Get();
+	if i == nil {
+		return nil;
+	}
+	return NewValue(i);
+}
+
 func interfaceCreator(typ Type, addr Addr) Value {
 	return &interfaceValueStruct{ commonValue{InterfaceKind, typ, addr} }
 }
-- 
2.48.1