printf as we know and love it.

Plus print[ln] with the ability to print struct values.

Note for language mavens: if a "..." function passes its argument
to another "..." function, the argument is not wrapped again.  This
allows printf to call fprintf without extra manipulation. It's good
but needs to go in the spec.

This code works:
///
package main

import fmt "fmt"
import os "os"

type T struct { s string; a, b int }

func main() {
	P := fmt.Printer();
	P.printf("%s = %d with float value %.4f\n", "hi there", 7, 123.456);
	P.println("hi there", 7, 123.456);
	P.fprintf(os.Stdout, "%s = %d with float value %.4f\n", "hi there", 7, 123.456);
	P.println(T{"x", 7, 234}, "end of struct", 8, 9);
}

R=rsc
DELTA=28  (7 added, 3 deleted, 18 changed)
OCL=18321
CL=18324

src/lib/fmt/print.go

@@ -83,11 +83,11 @@ export type Writer interface {
 }
 
 func (p *P) doprintf(format string, v reflect.StructValue);
-func (p *P) doprint(v reflect.StructValue, addspace bool);
+func (p *P) doprint(v reflect.StructValue, addspace, addnewline bool);
 
 // These routines end in 'f' and take a format string.
 
-func (p *P) fprintf(w Writer, format string, a reflect.Empty) (n int, error *os.Error) {
+func (p *P) fprintf(w Writer, format string, a ...) (n int, error *os.Error) {
 	v := reflect.NewValue(a).(reflect.PtrValue).Sub().(reflect.StructValue);
 	p.doprintf(format, v);
 	n, error = w.Write(p.buf[0:p.n]);
@@ -95,12 +95,12 @@ func (p *P) fprintf(w Writer, format string, a reflect.Empty) (n int, error *os.
 	return n, error;
 }
 
-func (p *P) printf(format string, v reflect.Empty) (n int, errno *os.Error) {
+func (p *P) printf(format string, v ...) (n int, errno *os.Error) {
 	n, errno = p.fprintf(os.Stdout, format, v);
 	return n, errno;
 }
 
-func (p *P) sprintf(format string, v reflect.Empty) string {
+func (p *P) sprintf(format string, v ...) string {
 	p.doprintf(format, reflect.NewValue(v).(reflect.StructValue));
 	s := string(p.buf)[0 : p.n];
 	p.reset();
@@ -110,21 +110,21 @@ func (p *P) sprintf(format string, v reflect.Empty) string {
 // These routines do not take a format string and add spaces only
 // when the operand on neither side is a string.
 
-func (p *P) fprint(w Writer, a reflect.Empty) (n int, error *os.Error) {
+func (p *P) fprint(w Writer, a ...) (n int, error *os.Error) {
 	v := reflect.NewValue(a).(reflect.PtrValue).Sub().(reflect.StructValue);
-	p.doprint(v, false);
+	p.doprint(v, false, false);
 	n, error = w.Write(p.buf[0:p.n]);
 	p.reset();
 	return n, error;
 }
 
-func (p *P) print(v reflect.Empty) (n int, errno *os.Error) {
+func (p *P) print(v ...) (n int, errno *os.Error) {
 	n, errno = p.fprint(os.Stdout, v);
 	return n, errno;
 }
 
-func (p *P) sprint(v reflect.Empty) string {
-	p.doprint(reflect.NewValue(v).(reflect.StructValue), false);
+func (p *P) sprint(v ...) string {
+	p.doprint(reflect.NewValue(v).(reflect.StructValue), false, false);
 	s := string(p.buf)[0 : p.n];
 	p.reset();
 	return s;
@@ -134,21 +134,21 @@ func (p *P) sprint(v reflect.Empty) string {
 // always add spaces between operands, and add a newline
 // after the last operand.
 
-func (p *P) fprintln(w Writer, a reflect.Empty) (n int, error *os.Error) {
+func (p *P) fprintln(w Writer, a ...) (n int, error *os.Error) {
 	v := reflect.NewValue(a).(reflect.PtrValue).Sub().(reflect.StructValue);
-	p.doprint(v, true);
+	p.doprint(v, true, true);
 	n, error = w.Write(p.buf[0:p.n]);
 	p.reset();
 	return n, error;
 }
 
-func (p *P) println(v reflect.Empty) (n int, errno *os.Error) {
+func (p *P) println(v ...) (n int, errno *os.Error) {
 	n, errno = p.fprintln(os.Stdout, v);
 	return n, errno;
 }
 
-func (p *P) sprintln(v reflect.Empty) string {
-	p.doprint(reflect.NewValue(v).(reflect.StructValue), true);
+func (p *P) sprintln(v ...) string {
+	p.doprint(reflect.NewValue(v).(reflect.StructValue), true, true);
 	s := string(p.buf)[0 : p.n];
 	p.reset();
 	return s;
@@ -362,19 +362,19 @@ func (p *P) doprintf(format string, v reflect.StructValue) {
 	}
 }
 
-func (p *P) doprint(v reflect.StructValue, is_println bool) {
+func (p *P) doprint(v reflect.StructValue, addspace, addnewline bool) {
 	prev_string := false;
 	for fieldnum := 0; fieldnum < v.Len();  fieldnum++ {
 		// always add spaces if we're doing println
 		field := v.Field(fieldnum);
 		s := "";
-		if is_println {
-			if fieldnum > 0 {
+		if fieldnum > 0 {
+			if addspace {
+				p.add(' ')
+			} else if field.Kind() != reflect.StringKind && !prev_string{
+				// if not doing println, add spaces if neither side is a string
 				p.add(' ')
 			}
-		} else if field.Kind() != reflect.StringKind && !prev_string{
-			// if not doing println, add spaces if neither side is a string
-			p.add(' ')
 		}
 		switch field.Kind() {
 		case reflect.BoolKind:
@@ -396,13 +396,17 @@ func (p *P) doprint(v reflect.StructValue, is_println bool) {
 			p.add('0');
 			p.add('x');
 			s = p.fmt.uX64(v).str();
+		case reflect.StructKind:
+			p.add('{');
+			p.doprint(field, true, false);
+			p.add('}');
 		default:
 			s = "???";
 		}
 		p.addstr(s);
 		prev_string = field.Kind() == reflect.StringKind;
 	}
-	if is_println {
+	if addnewline {
 		p.add('\n')
 	}
 }