...
Run Format

Source file src/fmt/print.go

  // Copyright 2009 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package fmt
  
  import (
  	"errors"
  	"io"
  	"os"
  	"reflect"
  	"sync"
  	"unicode/utf8"
  )
  
  // Strings for use with buffer.WriteString.
  // This is less overhead than using buffer.Write with byte arrays.
  const (
  	commaSpaceString  = ", "
  	nilAngleString    = "<nil>"
  	nilParenString    = "(nil)"
  	nilString         = "nil"
  	mapString         = "map["
  	percentBangString = "%!"
  	missingString     = "(MISSING)"
  	badIndexString    = "(BADINDEX)"
  	panicString       = "(PANIC="
  	extraString       = "%!(EXTRA "
  	badWidthString    = "%!(BADWIDTH)"
  	badPrecString     = "%!(BADPREC)"
  	noVerbString      = "%!(NOVERB)"
  	invReflectString  = "<invalid reflect.Value>"
  )
  
  // State represents the printer state passed to custom formatters.
  // It provides access to the io.Writer interface plus information about
  // the flags and options for the operand's format specifier.
  type State interface {
  	// Write is the function to call to emit formatted output to be printed.
  	Write(b []byte) (n int, err error)
  	// Width returns the value of the width option and whether it has been set.
  	Width() (wid int, ok bool)
  	// Precision returns the value of the precision option and whether it has been set.
  	Precision() (prec int, ok bool)
  
  	// Flag reports whether the flag c, a character, has been set.
  	Flag(c int) bool
  }
  
  // Formatter is the interface implemented by values with a custom formatter.
  // The implementation of Format may call Sprint(f) or Fprint(f) etc.
  // to generate its output.
  type Formatter interface {
  	Format(f State, c rune)
  }
  
  // Stringer is implemented by any value that has a String method,
  // which defines the ``native'' format for that value.
  // The String method is used to print values passed as an operand
  // to any format that accepts a string or to an unformatted printer
  // such as Print.
  type Stringer interface {
  	String() string
  }
  
  // GoStringer is implemented by any value that has a GoString method,
  // which defines the Go syntax for that value.
  // The GoString method is used to print values passed as an operand
  // to a %#v format.
  type GoStringer interface {
  	GoString() string
  }
  
  // Use simple []byte instead of bytes.Buffer to avoid large dependency.
  type buffer []byte
  
  func (b *buffer) Write(p []byte) {
  	*b = append(*b, p...)
  }
  
  func (b *buffer) WriteString(s string) {
  	*b = append(*b, s...)
  }
  
  func (b *buffer) WriteByte(c byte) {
  	*b = append(*b, c)
  }
  
  func (bp *buffer) WriteRune(r rune) {
  	if r < utf8.RuneSelf {
  		*bp = append(*bp, byte(r))
  		return
  	}
  
  	b := *bp
  	n := len(b)
  	for n+utf8.UTFMax > cap(b) {
  		b = append(b, 0)
  	}
  	w := utf8.EncodeRune(b[n:n+utf8.UTFMax], r)
  	*bp = b[:n+w]
  }
  
  // pp is used to store a printer's state and is reused with sync.Pool to avoid allocations.
  type pp struct {
  	buf buffer
  
  	// arg holds the current item, as an interface{}.
  	arg interface{}
  
  	// value is used instead of arg for reflect values.
  	value reflect.Value
  
  	// fmt is used to format basic items such as integers or strings.
  	fmt fmt
  
  	// reordered records whether the format string used argument reordering.
  	reordered bool
  	// goodArgNum records whether the most recent reordering directive was valid.
  	goodArgNum bool
  	// panicking is set by catchPanic to avoid infinite panic, recover, panic, ... recursion.
  	panicking bool
  	// erroring is set when printing an error string to guard against calling handleMethods.
  	erroring bool
  }
  
  var ppFree = sync.Pool{
  	New: func() interface{} { return new(pp) },
  }
  
  // newPrinter allocates a new pp struct or grabs a cached one.
  func newPrinter() *pp {
  	p := ppFree.Get().(*pp)
  	p.panicking = false
  	p.erroring = false
  	p.fmt.init(&p.buf)
  	return p
  }
  
  // free saves used pp structs in ppFree; avoids an allocation per invocation.
  func (p *pp) free() {
  	p.buf = p.buf[:0]
  	p.arg = nil
  	p.value = reflect.Value{}
  	ppFree.Put(p)
  }
  
  func (p *pp) Width() (wid int, ok bool) { return p.fmt.wid, p.fmt.widPresent }
  
  func (p *pp) Precision() (prec int, ok bool) { return p.fmt.prec, p.fmt.precPresent }
  
  func (p *pp) Flag(b int) bool {
  	switch b {
  	case '-':
  		return p.fmt.minus
  	case '+':
  		return p.fmt.plus || p.fmt.plusV
  	case '#':
  		return p.fmt.sharp || p.fmt.sharpV
  	case ' ':
  		return p.fmt.space
  	case '0':
  		return p.fmt.zero
  	}
  	return false
  }
  
  // Implement Write so we can call Fprintf on a pp (through State), for
  // recursive use in custom verbs.
  func (p *pp) Write(b []byte) (ret int, err error) {
  	p.buf.Write(b)
  	return len(b), nil
  }
  
  // These routines end in 'f' and take a format string.
  
  // Fprintf formats according to a format specifier and writes to w.
  // It returns the number of bytes written and any write error encountered.
  func Fprintf(w io.Writer, format string, a ...interface{}) (n int, err error) {
  	p := newPrinter()
  	p.doPrintf(format, a)
  	n, err = w.Write(p.buf)
  	p.free()
  	return
  }
  
  // Printf formats according to a format specifier and writes to standard output.
  // It returns the number of bytes written and any write error encountered.
  func Printf(format string, a ...interface{}) (n int, err error) {
  	return Fprintf(os.Stdout, format, a...)
  }
  
  // Sprintf formats according to a format specifier and returns the resulting string.
  func Sprintf(format string, a ...interface{}) string {
  	p := newPrinter()
  	p.doPrintf(format, a)
  	s := string(p.buf)
  	p.free()
  	return s
  }
  
  // Errorf formats according to a format specifier and returns the string
  // as a value that satisfies error.
  func Errorf(format string, a ...interface{}) error {
  	return errors.New(Sprintf(format, a...))
  }
  
  // These routines do not take a format string
  
  // Fprint formats using the default formats for its operands and writes to w.
  // Spaces are added between operands when neither is a string.
  // It returns the number of bytes written and any write error encountered.
  func Fprint(w io.Writer, a ...interface{}) (n int, err error) {
  	p := newPrinter()
  	p.doPrint(a)
  	n, err = w.Write(p.buf)
  	p.free()
  	return
  }
  
  // Print formats using the default formats for its operands and writes to standard output.
  // Spaces are added between operands when neither is a string.
  // It returns the number of bytes written and any write error encountered.
  func Print(a ...interface{}) (n int, err error) {
  	return Fprint(os.Stdout, a...)
  }
  
  // Sprint formats using the default formats for its operands and returns the resulting string.
  // Spaces are added between operands when neither is a string.
  func Sprint(a ...interface{}) string {
  	p := newPrinter()
  	p.doPrint(a)
  	s := string(p.buf)
  	p.free()
  	return s
  }
  
  // These routines end in 'ln', do not take a format string,
  // always add spaces between operands, and add a newline
  // after the last operand.
  
  // Fprintln formats using the default formats for its operands and writes to w.
  // Spaces are always added between operands and a newline is appended.
  // It returns the number of bytes written and any write error encountered.
  func Fprintln(w io.Writer, a ...interface{}) (n int, err error) {
  	p := newPrinter()
  	p.doPrintln(a)
  	n, err = w.Write(p.buf)
  	p.free()
  	return
  }
  
  // Println formats using the default formats for its operands and writes to standard output.
  // Spaces are always added between operands and a newline is appended.
  // It returns the number of bytes written and any write error encountered.
  func Println(a ...interface{}) (n int, err error) {
  	return Fprintln(os.Stdout, a...)
  }
  
  // Sprintln formats using the default formats for its operands and returns the resulting string.
  // Spaces are always added between operands and a newline is appended.
  func Sprintln(a ...interface{}) string {
  	p := newPrinter()
  	p.doPrintln(a)
  	s := string(p.buf)
  	p.free()
  	return s
  }
  
  // getField gets the i'th field of the struct value.
  // If the field is itself is an interface, return a value for
  // the thing inside the interface, not the interface itself.
  func getField(v reflect.Value, i int) reflect.Value {
  	val := v.Field(i)
  	if val.Kind() == reflect.Interface && !val.IsNil() {
  		val = val.Elem()
  	}
  	return val
  }
  
  // tooLarge reports whether the magnitude of the integer is
  // too large to be used as a formatting width or precision.
  func tooLarge(x int) bool {
  	const max int = 1e6
  	return x > max || x < -max
  }
  
  // parsenum converts ASCII to integer.  num is 0 (and isnum is false) if no number present.
  func parsenum(s string, start, end int) (num int, isnum bool, newi int) {
  	if start >= end {
  		return 0, false, end
  	}
  	for newi = start; newi < end && '0' <= s[newi] && s[newi] <= '9'; newi++ {
  		if tooLarge(num) {
  			return 0, false, end // Overflow; crazy long number most likely.
  		}
  		num = num*10 + int(s[newi]-'0')
  		isnum = true
  	}
  	return
  }
  
  func (p *pp) unknownType(v reflect.Value) {
  	if !v.IsValid() {
  		p.buf.WriteString(nilAngleString)
  		return
  	}
  	p.buf.WriteByte('?')
  	p.buf.WriteString(v.Type().String())
  	p.buf.WriteByte('?')
  }
  
  func (p *pp) badVerb(verb rune) {
  	p.erroring = true
  	p.buf.WriteString(percentBangString)
  	p.buf.WriteRune(verb)
  	p.buf.WriteByte('(')
  	switch {
  	case p.arg != nil:
  		p.buf.WriteString(reflect.TypeOf(p.arg).String())
  		p.buf.WriteByte('=')
  		p.printArg(p.arg, 'v')
  	case p.value.IsValid():
  		p.buf.WriteString(p.value.Type().String())
  		p.buf.WriteByte('=')
  		p.printValue(p.value, 'v', 0)
  	default:
  		p.buf.WriteString(nilAngleString)
  	}
  	p.buf.WriteByte(')')
  	p.erroring = false
  }
  
  func (p *pp) fmtBool(v bool, verb rune) {
  	switch verb {
  	case 't', 'v':
  		p.fmt.fmt_boolean(v)
  	default:
  		p.badVerb(verb)
  	}
  }
  
  // fmt0x64 formats a uint64 in hexadecimal and prefixes it with 0x or
  // not, as requested, by temporarily setting the sharp flag.
  func (p *pp) fmt0x64(v uint64, leading0x bool) {
  	sharp := p.fmt.sharp
  	p.fmt.sharp = leading0x
  	p.fmt.fmt_integer(v, 16, unsigned, ldigits)
  	p.fmt.sharp = sharp
  }
  
  // fmtInteger formats a signed or unsigned integer.
  func (p *pp) fmtInteger(v uint64, isSigned bool, verb rune) {
  	switch verb {
  	case 'v':
  		if p.fmt.sharpV && !isSigned {
  			p.fmt0x64(v, true)
  		} else {
  			p.fmt.fmt_integer(v, 10, isSigned, ldigits)
  		}
  	case 'd':
  		p.fmt.fmt_integer(v, 10, isSigned, ldigits)
  	case 'b':
  		p.fmt.fmt_integer(v, 2, isSigned, ldigits)
  	case 'o':
  		p.fmt.fmt_integer(v, 8, isSigned, ldigits)
  	case 'x':
  		p.fmt.fmt_integer(v, 16, isSigned, ldigits)
  	case 'X':
  		p.fmt.fmt_integer(v, 16, isSigned, udigits)
  	case 'c':
  		p.fmt.fmt_c(v)
  	case 'q':
  		if v <= utf8.MaxRune {
  			p.fmt.fmt_qc(v)
  		} else {
  			p.badVerb(verb)
  		}
  	case 'U':
  		p.fmt.fmt_unicode(v)
  	default:
  		p.badVerb(verb)
  	}
  }
  
  // fmtFloat formats a float. The default precision for each verb
  // is specified as last argument in the call to fmt_float.
  func (p *pp) fmtFloat(v float64, size int, verb rune) {
  	switch verb {
  	case 'v':
  		p.fmt.fmt_float(v, size, 'g', -1)
  	case 'b', 'g', 'G':
  		p.fmt.fmt_float(v, size, verb, -1)
  	case 'f', 'e', 'E':
  		p.fmt.fmt_float(v, size, verb, 6)
  	case 'F':
  		p.fmt.fmt_float(v, size, 'f', 6)
  	default:
  		p.badVerb(verb)
  	}
  }
  
  // fmtComplex formats a complex number v with
  // r = real(v) and j = imag(v) as (r+ji) using
  // fmtFloat for r and j formatting.
  func (p *pp) fmtComplex(v complex128, size int, verb rune) {
  	// Make sure any unsupported verbs are found before the
  	// calls to fmtFloat to not generate an incorrect error string.
  	switch verb {
  	case 'v', 'b', 'g', 'G', 'f', 'F', 'e', 'E':
  		oldPlus := p.fmt.plus
  		p.buf.WriteByte('(')
  		p.fmtFloat(real(v), size/2, verb)
  		// Imaginary part always has a sign.
  		p.fmt.plus = true
  		p.fmtFloat(imag(v), size/2, verb)
  		p.buf.WriteString("i)")
  		p.fmt.plus = oldPlus
  	default:
  		p.badVerb(verb)
  	}
  }
  
  func (p *pp) fmtString(v string, verb rune) {
  	switch verb {
  	case 'v':
  		if p.fmt.sharpV {
  			p.fmt.fmt_q(v)
  		} else {
  			p.fmt.fmt_s(v)
  		}
  	case 's':
  		p.fmt.fmt_s(v)
  	case 'x':
  		p.fmt.fmt_sx(v, ldigits)
  	case 'X':
  		p.fmt.fmt_sx(v, udigits)
  	case 'q':
  		p.fmt.fmt_q(v)
  	default:
  		p.badVerb(verb)
  	}
  }
  
  func (p *pp) fmtBytes(v []byte, verb rune, typeString string) {
  	switch verb {
  	case 'v', 'd':
  		if p.fmt.sharpV {
  			p.buf.WriteString(typeString)
  			if v == nil {
  				p.buf.WriteString(nilParenString)
  				return
  			}
  			p.buf.WriteByte('{')
  			for i, c := range v {
  				if i > 0 {
  					p.buf.WriteString(commaSpaceString)
  				}
  				p.fmt0x64(uint64(c), true)
  			}
  			p.buf.WriteByte('}')
  		} else {
  			p.buf.WriteByte('[')
  			for i, c := range v {
  				if i > 0 {
  					p.buf.WriteByte(' ')
  				}
  				p.fmt.fmt_integer(uint64(c), 10, unsigned, ldigits)
  			}
  			p.buf.WriteByte(']')
  		}
  	case 's':
  		p.fmt.fmt_s(string(v))
  	case 'x':
  		p.fmt.fmt_bx(v, ldigits)
  	case 'X':
  		p.fmt.fmt_bx(v, udigits)
  	case 'q':
  		p.fmt.fmt_q(string(v))
  	default:
  		p.printValue(reflect.ValueOf(v), verb, 0)
  	}
  }
  
  func (p *pp) fmtPointer(value reflect.Value, verb rune) {
  	var u uintptr
  	switch value.Kind() {
  	case reflect.Chan, reflect.Func, reflect.Map, reflect.Ptr, reflect.Slice, reflect.UnsafePointer:
  		u = value.Pointer()
  	default:
  		p.badVerb(verb)
  		return
  	}
  
  	switch verb {
  	case 'v':
  		if p.fmt.sharpV {
  			p.buf.WriteByte('(')
  			p.buf.WriteString(value.Type().String())
  			p.buf.WriteString(")(")
  			if u == 0 {
  				p.buf.WriteString(nilString)
  			} else {
  				p.fmt0x64(uint64(u), true)
  			}
  			p.buf.WriteByte(')')
  		} else {
  			if u == 0 {
  				p.fmt.padString(nilAngleString)
  			} else {
  				p.fmt0x64(uint64(u), !p.fmt.sharp)
  			}
  		}
  	case 'p':
  		p.fmt0x64(uint64(u), !p.fmt.sharp)
  	case 'b', 'o', 'd', 'x', 'X':
  		p.fmtInteger(uint64(u), unsigned, verb)
  	default:
  		p.badVerb(verb)
  	}
  }
  
  func (p *pp) catchPanic(arg interface{}, verb rune) {
  	if err := recover(); err != nil {
  		// If it's a nil pointer, just say "<nil>". The likeliest causes are a
  		// Stringer that fails to guard against nil or a nil pointer for a
  		// value receiver, and in either case, "<nil>" is a nice result.
  		if v := reflect.ValueOf(arg); v.Kind() == reflect.Ptr && v.IsNil() {
  			p.buf.WriteString(nilAngleString)
  			return
  		}
  		// Otherwise print a concise panic message. Most of the time the panic
  		// value will print itself nicely.
  		if p.panicking {
  			// Nested panics; the recursion in printArg cannot succeed.
  			panic(err)
  		}
  
  		oldFlags := p.fmt.fmtFlags
  		// For this output we want default behavior.
  		p.fmt.clearflags()
  
  		p.buf.WriteString(percentBangString)
  		p.buf.WriteRune(verb)
  		p.buf.WriteString(panicString)
  		p.panicking = true
  		p.printArg(err, 'v')
  		p.panicking = false
  		p.buf.WriteByte(')')
  
  		p.fmt.fmtFlags = oldFlags
  	}
  }
  
  func (p *pp) handleMethods(verb rune) (handled bool) {
  	if p.erroring {
  		return
  	}
  	// Is it a Formatter?
  	if formatter, ok := p.arg.(Formatter); ok {
  		handled = true
  		defer p.catchPanic(p.arg, verb)
  		formatter.Format(p, verb)
  		return
  	}
  
  	// If we're doing Go syntax and the argument knows how to supply it, take care of it now.
  	if p.fmt.sharpV {
  		if stringer, ok := p.arg.(GoStringer); ok {
  			handled = true
  			defer p.catchPanic(p.arg, verb)
  			// Print the result of GoString unadorned.
  			p.fmt.fmt_s(stringer.GoString())
  			return
  		}
  	} else {
  		// If a string is acceptable according to the format, see if
  		// the value satisfies one of the string-valued interfaces.
  		// Println etc. set verb to %v, which is "stringable".
  		switch verb {
  		case 'v', 's', 'x', 'X', 'q':
  			// Is it an error or Stringer?
  			// The duplication in the bodies is necessary:
  			// setting handled and deferring catchPanic
  			// must happen before calling the method.
  			switch v := p.arg.(type) {
  			case error:
  				handled = true
  				defer p.catchPanic(p.arg, verb)
  				p.fmtString(v.Error(), verb)
  				return
  
  			case Stringer:
  				handled = true
  				defer p.catchPanic(p.arg, verb)
  				p.fmtString(v.String(), verb)
  				return
  			}
  		}
  	}
  	return false
  }
  
  func (p *pp) printArg(arg interface{}, verb rune) {
  	p.arg = arg
  	p.value = reflect.Value{}
  
  	if arg == nil {
  		switch verb {
  		case 'T', 'v':
  			p.fmt.padString(nilAngleString)
  		default:
  			p.badVerb(verb)
  		}
  		return
  	}
  
  	// Special processing considerations.
  	// %T (the value's type) and %p (its address) are special; we always do them first.
  	switch verb {
  	case 'T':
  		p.fmt.fmt_s(reflect.TypeOf(arg).String())
  		return
  	case 'p':
  		p.fmtPointer(reflect.ValueOf(arg), 'p')
  		return
  	}
  
  	// Some types can be done without reflection.
  	switch f := arg.(type) {
  	case bool:
  		p.fmtBool(f, verb)
  	case float32:
  		p.fmtFloat(float64(f), 32, verb)
  	case float64:
  		p.fmtFloat(f, 64, verb)
  	case complex64:
  		p.fmtComplex(complex128(f), 64, verb)
  	case complex128:
  		p.fmtComplex(f, 128, verb)
  	case int:
  		p.fmtInteger(uint64(f), signed, verb)
  	case int8:
  		p.fmtInteger(uint64(f), signed, verb)
  	case int16:
  		p.fmtInteger(uint64(f), signed, verb)
  	case int32:
  		p.fmtInteger(uint64(f), signed, verb)
  	case int64:
  		p.fmtInteger(uint64(f), signed, verb)
  	case uint:
  		p.fmtInteger(uint64(f), unsigned, verb)
  	case uint8:
  		p.fmtInteger(uint64(f), unsigned, verb)
  	case uint16:
  		p.fmtInteger(uint64(f), unsigned, verb)
  	case uint32:
  		p.fmtInteger(uint64(f), unsigned, verb)
  	case uint64:
  		p.fmtInteger(f, unsigned, verb)
  	case uintptr:
  		p.fmtInteger(uint64(f), unsigned, verb)
  	case string:
  		p.fmtString(f, verb)
  	case []byte:
  		p.fmtBytes(f, verb, "[]byte")
  	case reflect.Value:
  		// Handle extractable values with special methods
  		// since printValue does not handle them at depth 0.
  		if f.IsValid() && f.CanInterface() {
  			p.arg = f.Interface()
  			if p.handleMethods(verb) {
  				return
  			}
  		}
  		p.printValue(f, verb, 0)
  	default:
  		// If the type is not simple, it might have methods.
  		if !p.handleMethods(verb) {
  			// Need to use reflection, since the type had no
  			// interface methods that could be used for formatting.
  			p.printValue(reflect.ValueOf(f), verb, 0)
  		}
  	}
  }
  
  var byteType = reflect.TypeOf(byte(0))
  
  // printValue is similar to printArg but starts with a reflect value, not an interface{} value.
  // It does not handle 'p' and 'T' verbs because these should have been already handled by printArg.
  func (p *pp) printValue(value reflect.Value, verb rune, depth int) {
  	// Handle values with special methods if not already handled by printArg (depth == 0).
  	if depth > 0 && value.IsValid() && value.CanInterface() {
  		p.arg = value.Interface()
  		if p.handleMethods(verb) {
  			return
  		}
  	}
  	p.arg = nil
  	p.value = value
  
  	switch f := value; value.Kind() {
  	case reflect.Invalid:
  		if depth == 0 {
  			p.buf.WriteString(invReflectString)
  		} else {
  			switch verb {
  			case 'v':
  				p.buf.WriteString(nilAngleString)
  			default:
  				p.badVerb(verb)
  			}
  		}
  	case reflect.Bool:
  		p.fmtBool(f.Bool(), verb)
  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
  		p.fmtInteger(uint64(f.Int()), signed, verb)
  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
  		p.fmtInteger(f.Uint(), unsigned, verb)
  	case reflect.Float32:
  		p.fmtFloat(f.Float(), 32, verb)
  	case reflect.Float64:
  		p.fmtFloat(f.Float(), 64, verb)
  	case reflect.Complex64:
  		p.fmtComplex(f.Complex(), 64, verb)
  	case reflect.Complex128:
  		p.fmtComplex(f.Complex(), 128, verb)
  	case reflect.String:
  		p.fmtString(f.String(), verb)
  	case reflect.Map:
  		if p.fmt.sharpV {
  			p.buf.WriteString(f.Type().String())
  			if f.IsNil() {
  				p.buf.WriteString(nilParenString)
  				return
  			}
  			p.buf.WriteByte('{')
  		} else {
  			p.buf.WriteString(mapString)
  		}
  		keys := f.MapKeys()
  		for i, key := range keys {
  			if i > 0 {
  				if p.fmt.sharpV {
  					p.buf.WriteString(commaSpaceString)
  				} else {
  					p.buf.WriteByte(' ')
  				}
  			}
  			p.printValue(key, verb, depth+1)
  			p.buf.WriteByte(':')
  			p.printValue(f.MapIndex(key), verb, depth+1)
  		}
  		if p.fmt.sharpV {
  			p.buf.WriteByte('}')
  		} else {
  			p.buf.WriteByte(']')
  		}
  	case reflect.Struct:
  		if p.fmt.sharpV {
  			p.buf.WriteString(f.Type().String())
  		}
  		p.buf.WriteByte('{')
  		for i := 0; i < f.NumField(); i++ {
  			if i > 0 {
  				if p.fmt.sharpV {
  					p.buf.WriteString(commaSpaceString)
  				} else {
  					p.buf.WriteByte(' ')
  				}
  			}
  			if p.fmt.plusV || p.fmt.sharpV {
  				if name := f.Type().Field(i).Name; name != "" {
  					p.buf.WriteString(name)
  					p.buf.WriteByte(':')
  				}
  			}
  			p.printValue(getField(f, i), verb, depth+1)
  		}
  		p.buf.WriteByte('}')
  	case reflect.Interface:
  		value := f.Elem()
  		if !value.IsValid() {
  			if p.fmt.sharpV {
  				p.buf.WriteString(f.Type().String())
  				p.buf.WriteString(nilParenString)
  			} else {
  				p.buf.WriteString(nilAngleString)
  			}
  		} else {
  			p.printValue(value, verb, depth+1)
  		}
  	case reflect.Array, reflect.Slice:
  		switch verb {
  		case 's', 'q', 'x', 'X':
  			// Handle byte and uint8 slices and arrays special for the above verbs.
  			t := f.Type()
  			if t.Elem().Kind() == reflect.Uint8 {
  				var bytes []byte
  				if f.Kind() == reflect.Slice {
  					bytes = f.Bytes()
  				} else if f.CanAddr() {
  					bytes = f.Slice(0, f.Len()).Bytes()
  				} else {
  					// We have an array, but we cannot Slice() a non-addressable array,
  					// so we build a slice by hand. This is a rare case but it would be nice
  					// if reflection could help a little more.
  					bytes = make([]byte, f.Len())
  					for i := range bytes {
  						bytes[i] = byte(f.Index(i).Uint())
  					}
  				}
  				p.fmtBytes(bytes, verb, t.String())
  				return
  			}
  		}
  		if p.fmt.sharpV {
  			p.buf.WriteString(f.Type().String())
  			if f.Kind() == reflect.Slice && f.IsNil() {
  				p.buf.WriteString(nilParenString)
  				return
  			}
  			p.buf.WriteByte('{')
  			for i := 0; i < f.Len(); i++ {
  				if i > 0 {
  					p.buf.WriteString(commaSpaceString)
  				}
  				p.printValue(f.Index(i), verb, depth+1)
  			}
  			p.buf.WriteByte('}')
  		} else {
  			p.buf.WriteByte('[')
  			for i := 0; i < f.Len(); i++ {
  				if i > 0 {
  					p.buf.WriteByte(' ')
  				}
  				p.printValue(f.Index(i), verb, depth+1)
  			}
  			p.buf.WriteByte(']')
  		}
  	case reflect.Ptr:
  		// pointer to array or slice or struct?  ok at top level
  		// but not embedded (avoid loops)
  		if depth == 0 && f.Pointer() != 0 {
  			switch a := f.Elem(); a.Kind() {
  			case reflect.Array, reflect.Slice, reflect.Struct, reflect.Map:
  				p.buf.WriteByte('&')
  				p.printValue(a, verb, depth+1)
  				return
  			}
  		}
  		fallthrough
  	case reflect.Chan, reflect.Func, reflect.UnsafePointer:
  		p.fmtPointer(f, verb)
  	default:
  		p.unknownType(f)
  	}
  }
  
  // intFromArg gets the argNumth element of a. On return, isInt reports whether the argument has integer type.
  func intFromArg(a []interface{}, argNum int) (num int, isInt bool, newArgNum int) {
  	newArgNum = argNum
  	if argNum < len(a) {
  		num, isInt = a[argNum].(int) // Almost always OK.
  		if !isInt {
  			// Work harder.
  			switch v := reflect.ValueOf(a[argNum]); v.Kind() {
  			case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
  				n := v.Int()
  				if int64(int(n)) == n {
  					num = int(n)
  					isInt = true
  				}
  			case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
  				n := v.Uint()
  				if int64(n) >= 0 && uint64(int(n)) == n {
  					num = int(n)
  					isInt = true
  				}
  			default:
  				// Already 0, false.
  			}
  		}
  		newArgNum = argNum + 1
  		if tooLarge(num) {
  			num = 0
  			isInt = false
  		}
  	}
  	return
  }
  
  // parseArgNumber returns the value of the bracketed number, minus 1
  // (explicit argument numbers are one-indexed but we want zero-indexed).
  // The opening bracket is known to be present at format[0].
  // The returned values are the index, the number of bytes to consume
  // up to the closing paren, if present, and whether the number parsed
  // ok. The bytes to consume will be 1 if no closing paren is present.
  func parseArgNumber(format string) (index int, wid int, ok bool) {
  	// There must be at least 3 bytes: [n].
  	if len(format) < 3 {
  		return 0, 1, false
  	}
  
  	// Find closing bracket.
  	for i := 1; i < len(format); i++ {
  		if format[i] == ']' {
  			width, ok, newi := parsenum(format, 1, i)
  			if !ok || newi != i {
  				return 0, i + 1, false
  			}
  			return width - 1, i + 1, true // arg numbers are one-indexed and skip paren.
  		}
  	}
  	return 0, 1, false
  }
  
  // argNumber returns the next argument to evaluate, which is either the value of the passed-in
  // argNum or the value of the bracketed integer that begins format[i:]. It also returns
  // the new value of i, that is, the index of the next byte of the format to process.
  func (p *pp) argNumber(argNum int, format string, i int, numArgs int) (newArgNum, newi int, found bool) {
  	if len(format) <= i || format[i] != '[' {
  		return argNum, i, false
  	}
  	p.reordered = true
  	index, wid, ok := parseArgNumber(format[i:])
  	if ok && 0 <= index && index < numArgs {
  		return index, i + wid, true
  	}
  	p.goodArgNum = false
  	return argNum, i + wid, ok
  }
  
  func (p *pp) badArgNum(verb rune) {
  	p.buf.WriteString(percentBangString)
  	p.buf.WriteRune(verb)
  	p.buf.WriteString(badIndexString)
  }
  
  func (p *pp) missingArg(verb rune) {
  	p.buf.WriteString(percentBangString)
  	p.buf.WriteRune(verb)
  	p.buf.WriteString(missingString)
  }
  
  func (p *pp) doPrintf(format string, a []interface{}) {
  	end := len(format)
  	argNum := 0         // we process one argument per non-trivial format
  	afterIndex := false // previous item in format was an index like [3].
  	p.reordered = false
  formatLoop:
  	for i := 0; i < end; {
  		p.goodArgNum = true
  		lasti := i
  		for i < end && format[i] != '%' {
  			i++
  		}
  		if i > lasti {
  			p.buf.WriteString(format[lasti:i])
  		}
  		if i >= end {
  			// done processing format string
  			break
  		}
  
  		// Process one verb
  		i++
  
  		// Do we have flags?
  		p.fmt.clearflags()
  	simpleFormat:
  		for ; i < end; i++ {
  			c := format[i]
  			switch c {
  			case '#':
  				p.fmt.sharp = true
  			case '0':
  				p.fmt.zero = !p.fmt.minus // Only allow zero padding to the left.
  			case '+':
  				p.fmt.plus = true
  			case '-':
  				p.fmt.minus = true
  				p.fmt.zero = false // Do not pad with zeros to the right.
  			case ' ':
  				p.fmt.space = true
  			default:
  				// Fast path for common case of ascii lower case simple verbs
  				// without precision or width or argument indices.
  				if 'a' <= c && c <= 'z' && argNum < len(a) {
  					if c == 'v' {
  						// Go syntax
  						p.fmt.sharpV = p.fmt.sharp
  						p.fmt.sharp = false
  						// Struct-field syntax
  						p.fmt.plusV = p.fmt.plus
  						p.fmt.plus = false
  					}
  					p.printArg(a[argNum], rune(c))
  					argNum++
  					i++
  					continue formatLoop
  				}
  				// Format is more complex than simple flags and a verb or is malformed.
  				break simpleFormat
  			}
  		}
  
  		// Do we have an explicit argument index?
  		argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
  
  		// Do we have width?
  		if i < end && format[i] == '*' {
  			i++
  			p.fmt.wid, p.fmt.widPresent, argNum = intFromArg(a, argNum)
  
  			if !p.fmt.widPresent {
  				p.buf.WriteString(badWidthString)
  			}
  
  			// We have a negative width, so take its value and ensure
  			// that the minus flag is set
  			if p.fmt.wid < 0 {
  				p.fmt.wid = -p.fmt.wid
  				p.fmt.minus = true
  				p.fmt.zero = false // Do not pad with zeros to the right.
  			}
  			afterIndex = false
  		} else {
  			p.fmt.wid, p.fmt.widPresent, i = parsenum(format, i, end)
  			if afterIndex && p.fmt.widPresent { // "%[3]2d"
  				p.goodArgNum = false
  			}
  		}
  
  		// Do we have precision?
  		if i+1 < end && format[i] == '.' {
  			i++
  			if afterIndex { // "%[3].2d"
  				p.goodArgNum = false
  			}
  			argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
  			if i < end && format[i] == '*' {
  				i++
  				p.fmt.prec, p.fmt.precPresent, argNum = intFromArg(a, argNum)
  				// Negative precision arguments don't make sense
  				if p.fmt.prec < 0 {
  					p.fmt.prec = 0
  					p.fmt.precPresent = false
  				}
  				if !p.fmt.precPresent {
  					p.buf.WriteString(badPrecString)
  				}
  				afterIndex = false
  			} else {
  				p.fmt.prec, p.fmt.precPresent, i = parsenum(format, i, end)
  				if !p.fmt.precPresent {
  					p.fmt.prec = 0
  					p.fmt.precPresent = true
  				}
  			}
  		}
  
  		if !afterIndex {
  			argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
  		}
  
  		if i >= end {
  			p.buf.WriteString(noVerbString)
  			break
  		}
  
  		verb, w := utf8.DecodeRuneInString(format[i:])
  		i += w
  
  		switch {
  		case verb == '%': // Percent does not absorb operands and ignores f.wid and f.prec.
  			p.buf.WriteByte('%')
  		case !p.goodArgNum:
  			p.badArgNum(verb)
  		case argNum >= len(a): // No argument left over to print for the current verb.
  			p.missingArg(verb)
  		case verb == 'v':
  			// Go syntax
  			p.fmt.sharpV = p.fmt.sharp
  			p.fmt.sharp = false
  			// Struct-field syntax
  			p.fmt.plusV = p.fmt.plus
  			p.fmt.plus = false
  			fallthrough
  		default:
  			p.printArg(a[argNum], verb)
  			argNum++
  		}
  	}
  
  	// Check for extra arguments unless the call accessed the arguments
  	// out of order, in which case it's too expensive to detect if they've all
  	// been used and arguably OK if they're not.
  	if !p.reordered && argNum < len(a) {
  		p.fmt.clearflags()
  		p.buf.WriteString(extraString)
  		for i, arg := range a[argNum:] {
  			if i > 0 {
  				p.buf.WriteString(commaSpaceString)
  			}
  			if arg == nil {
  				p.buf.WriteString(nilAngleString)
  			} else {
  				p.buf.WriteString(reflect.TypeOf(arg).String())
  				p.buf.WriteByte('=')
  				p.printArg(arg, 'v')
  			}
  		}
  		p.buf.WriteByte(')')
  	}
  }
  
  func (p *pp) doPrint(a []interface{}) {
  	prevString := false
  	for argNum, arg := range a {
  		isString := arg != nil && reflect.TypeOf(arg).Kind() == reflect.String
  		// Add a space between two non-string arguments.
  		if argNum > 0 && !isString && !prevString {
  			p.buf.WriteByte(' ')
  		}
  		p.printArg(arg, 'v')
  		prevString = isString
  	}
  }
  
  // doPrintln is like doPrint but always adds a space between arguments
  // and a newline after the last argument.
  func (p *pp) doPrintln(a []interface{}) {
  	for argNum, arg := range a {
  		if argNum > 0 {
  			p.buf.WriteByte(' ')
  		}
  		p.printArg(arg, 'v')
  	}
  	p.buf.WriteByte('\n')
  }
  

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