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// 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 (
        "bytes"
        "errors"
        "io"
        "os"
        "reflect"
        "sync"
        "unicode"
        "unicode/utf8"
)

// Some constants in the form of bytes, to avoid string overhead.
// Needlessly fastidious, I suppose.
var (
        commaSpaceBytes = []byte(", ")
        nilAngleBytes   = []byte("<nil>")
        nilParenBytes   = []byte("(nil)")
        nilBytes        = []byte("nil")
        mapBytes        = []byte("map[")
        missingBytes    = []byte("(MISSING)")
        panicBytes      = []byte("(PANIC=")
        extraBytes      = []byte("%!(EXTRA ")
        irparenBytes    = []byte("i)")
        bytesBytes      = []byte("[]byte{")
        widthBytes      = []byte("%!(BADWIDTH)")
        precBytes       = []byte("%!(BADPREC)")
        noVerbBytes     = []byte("%!(NOVERB)")
)

// 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) (ret 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 returns 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 Sprintf or Fprintf(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 a %s or %v format 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
}

type pp struct {
        n         int
        panicking bool
        erroring  bool // printing an error condition
        buf       bytes.Buffer
        // field holds the current item, as an interface{}.
        field interface{}
        // value holds the current item, as a reflect.Value, and will be
        // the zero Value if the item has not been reflected.
        value   reflect.Value
        runeBuf [utf8.UTFMax]byte
        fmt     fmt
}

// A cache holds a set of reusable objects.
// The slice is a stack (LIFO).
// If more are needed, the cache creates them by calling new.
type cache struct {
        mu    sync.Mutex
        saved []interface{}
        new   func() interface{}
}

func (c *cache) put(x interface{}) {
        c.mu.Lock()
        if len(c.saved) < cap(c.saved) {
                c.saved = append(c.saved, x)
        }
        c.mu.Unlock()
}

func (c *cache) get() interface{} {
        c.mu.Lock()
        n := len(c.saved)
        if n == 0 {
                c.mu.Unlock()
                return c.new()
        }
        x := c.saved[n-1]
        c.saved = c.saved[0 : n-1]
        c.mu.Unlock()
        return x
}

func newCache(f func() interface{}) *cache {
        return &cache{saved: make([]interface{}, 0, 100), new: f}
}

var ppFree = newCache(func() interface{} { return new(pp) })

// Allocate a new pp struct or grab a cached one.
func newPrinter() *pp {
        p := ppFree.get().(*pp)
        p.panicking = false
        p.erroring = false
        p.fmt.init(&p.buf)
        return p
}

// Save used pp structs in ppFree; avoids an allocation per invocation.
func (p *pp) free() {
        // Don't hold on to pp structs with large buffers.
        if cap(p.buf.Bytes()) > 1024 {
                return
        }
        p.buf.Reset()
        p.field = 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
        case '#':
                return p.fmt.sharp
        case ' ':
                return p.fmt.space
        case '0':
                return p.fmt.zero
        }
        return false
}

func (p *pp) add(c rune) {
        p.buf.WriteRune(c)
}

// 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) {
        return p.buf.Write(b)
}

// 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)
        n64, err := p.buf.WriteTo(w)
        p.free()
        return int(n64), err
}

// 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 := p.buf.String()
        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, false, false)
        n64, err := p.buf.WriteTo(w)
        p.free()
        return int(n64), err
}

// 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, false, false)
        s := p.buf.String()
        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.doPrint(a, true, true)
        n64, err := p.buf.WriteTo(w)
        p.free()
        return int(n64), err
}

// 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.doPrint(a, true, true)
        s := p.buf.String()
        p.free()
        return s
}

// Get the i'th arg of the struct value.
// If the arg 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
}

// Convert ASCII to integer.  n is 0 (and got 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++ {
                num = num*10 + int(s[newi]-'0')
                isnum = true
        }
        return
}

func (p *pp) unknownType(v interface{}) {
        if v == nil {
                p.buf.Write(nilAngleBytes)
                return
        }
        p.buf.WriteByte('?')
        p.buf.WriteString(reflect.TypeOf(v).String())
        p.buf.WriteByte('?')
}

func (p *pp) badVerb(verb rune) {
        p.erroring = true
        p.add('%')
        p.add('!')
        p.add(verb)
        p.add('(')
        switch {
        case p.field != nil:
                p.buf.WriteString(reflect.TypeOf(p.field).String())
                p.add('=')
                p.printField(p.field, 'v', false, false, 0)
        case p.value.IsValid():
                p.buf.WriteString(p.value.Type().String())
                p.add('=')
                p.printValue(p.value, 'v', false, false, 0)
        default:
                p.buf.Write(nilAngleBytes)
        }
        p.add(')')
        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)
        }
}

// fmtC formats a rune for the 'c' format.
func (p *pp) fmtC(c int64) {
        r := rune(c) // Check for overflow.
        if int64(r) != c {
                r = utf8.RuneError
        }
        w := utf8.EncodeRune(p.runeBuf[0:utf8.UTFMax], r)
        p.fmt.pad(p.runeBuf[0:w])
}

func (p *pp) fmtInt64(v int64, verb rune) {
        switch verb {
        case 'b':
                p.fmt.integer(v, 2, signed, ldigits)
        case 'c':
                p.fmtC(v)
        case 'd', 'v':
                p.fmt.integer(v, 10, signed, ldigits)
        case 'o':
                p.fmt.integer(v, 8, signed, ldigits)
        case 'q':
                if 0 <= v && v <= unicode.MaxRune {
                        p.fmt.fmt_qc(v)
                } else {
                        p.badVerb(verb)
                }
        case 'x':
                p.fmt.integer(v, 16, signed, ldigits)
        case 'U':
                p.fmtUnicode(v)
        case 'X':
                p.fmt.integer(v, 16, signed, udigits)
        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.integer(int64(v), 16, unsigned, ldigits)
        p.fmt.sharp = sharp
}

// fmtUnicode formats a uint64 in U+1234 form by
// temporarily turning on the unicode flag and tweaking the precision.
func (p *pp) fmtUnicode(v int64) {
        precPresent := p.fmt.precPresent
        sharp := p.fmt.sharp
        p.fmt.sharp = false
        prec := p.fmt.prec
        if !precPresent {
                // If prec is already set, leave it alone; otherwise 4 is minimum.
                p.fmt.prec = 4
                p.fmt.precPresent = true
        }
        p.fmt.unicode = true // turn on U+
        p.fmt.uniQuote = sharp
        p.fmt.integer(int64(v), 16, unsigned, udigits)
        p.fmt.unicode = false
        p.fmt.uniQuote = false
        p.fmt.prec = prec
        p.fmt.precPresent = precPresent
        p.fmt.sharp = sharp
}

func (p *pp) fmtUint64(v uint64, verb rune, goSyntax bool) {
        switch verb {
        case 'b':
                p.fmt.integer(int64(v), 2, unsigned, ldigits)
        case 'c':
                p.fmtC(int64(v))
        case 'd':
                p.fmt.integer(int64(v), 10, unsigned, ldigits)
        case 'v':
                if goSyntax {
                        p.fmt0x64(v, true)
                } else {
                        p.fmt.integer(int64(v), 10, unsigned, ldigits)
                }
        case 'o':
                p.fmt.integer(int64(v), 8, unsigned, ldigits)
        case 'q':
                if 0 <= v && v <= unicode.MaxRune {
                        p.fmt.fmt_qc(int64(v))
                } else {
                        p.badVerb(verb)
                }
        case 'x':
                p.fmt.integer(int64(v), 16, unsigned, ldigits)
        case 'X':
                p.fmt.integer(int64(v), 16, unsigned, udigits)
        case 'U':
                p.fmtUnicode(int64(v))
        default:
                p.badVerb(verb)
        }
}

func (p *pp) fmtFloat32(v float32, verb rune) {
        switch verb {
        case 'b':
                p.fmt.fmt_fb32(v)
        case 'e':
                p.fmt.fmt_e32(v)
        case 'E':
                p.fmt.fmt_E32(v)
        case 'f':
                p.fmt.fmt_f32(v)
        case 'g', 'v':
                p.fmt.fmt_g32(v)
        case 'G':
                p.fmt.fmt_G32(v)
        default:
                p.badVerb(verb)
        }
}

func (p *pp) fmtFloat64(v float64, verb rune) {
        switch verb {
        case 'b':
                p.fmt.fmt_fb64(v)
        case 'e':
                p.fmt.fmt_e64(v)
        case 'E':
                p.fmt.fmt_E64(v)
        case 'f':
                p.fmt.fmt_f64(v)
        case 'g', 'v':
                p.fmt.fmt_g64(v)
        case 'G':
                p.fmt.fmt_G64(v)
        default:
                p.badVerb(verb)
        }
}

func (p *pp) fmtComplex64(v complex64, verb rune) {
        switch verb {
        case 'e', 'E', 'f', 'F', 'g', 'G':
                p.fmt.fmt_c64(v, verb)
        case 'v':
                p.fmt.fmt_c64(v, 'g')
        default:
                p.badVerb(verb)
        }
}

func (p *pp) fmtComplex128(v complex128, verb rune) {
        switch verb {
        case 'e', 'E', 'f', 'F', 'g', 'G':
                p.fmt.fmt_c128(v, verb)
        case 'v':
                p.fmt.fmt_c128(v, 'g')
        default:
                p.badVerb(verb)
        }
}

func (p *pp) fmtString(v string, verb rune, goSyntax bool) {
        switch verb {
        case 'v':
                if goSyntax {
                        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, goSyntax bool, depth int) {
        if verb == 'v' || verb == 'd' {
                if goSyntax {
                        p.buf.Write(bytesBytes)
                } else {
                        p.buf.WriteByte('[')
                }
                for i, c := range v {
                        if i > 0 {
                                if goSyntax {
                                        p.buf.Write(commaSpaceBytes)
                                } else {
                                        p.buf.WriteByte(' ')
                                }
                        }
                        p.printField(c, 'v', p.fmt.plus, goSyntax, depth+1)
                }
                if goSyntax {
                        p.buf.WriteByte('}')
                } else {
                        p.buf.WriteByte(']')
                }
                return
        }
        s := string(v)
        switch verb {
        case 's':
                p.fmt.fmt_s(s)
        case 'x':
                p.fmt.fmt_sx(s, ldigits)
        case 'X':
                p.fmt.fmt_sx(s, udigits)
        case 'q':
                p.fmt.fmt_q(s)
        default:
                p.badVerb(verb)
        }
}

func (p *pp) fmtPointer(value reflect.Value, verb rune, goSyntax bool) {
        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
        }
        if goSyntax {
                p.add('(')
                p.buf.WriteString(value.Type().String())
                p.add(')')
                p.add('(')
                if u == 0 {
                        p.buf.Write(nilBytes)
                } else {
                        p.fmt0x64(uint64(u), true)
                }
                p.add(')')
        } else {
                p.fmt0x64(uint64(u), !p.fmt.sharp)
        }
}

var (
        intBits     = reflect.TypeOf(0).Bits()
        floatBits   = reflect.TypeOf(0.0).Bits()
        complexBits = reflect.TypeOf(1i).Bits()
        uintptrBits = reflect.TypeOf(uintptr(0)).Bits()
)

func (p *pp) catchPanic(field 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(field); v.Kind() == reflect.Ptr && v.IsNil() {
                        p.buf.Write(nilAngleBytes)
                        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 printField cannot succeed.
                        panic(err)
                }
                p.buf.WriteByte('%')
                p.add(verb)
                p.buf.Write(panicBytes)
                p.panicking = true
                p.printField(err, 'v', false, false, 0)
                p.panicking = false
                p.buf.WriteByte(')')
        }
}

func (p *pp) handleMethods(verb rune, plus, goSyntax bool, depth int) (wasString, handled bool) {
        if p.erroring {
                return
        }
        // Is it a Formatter?
        if formatter, ok := p.field.(Formatter); ok {
                handled = true
                wasString = false
                defer p.catchPanic(p.field, verb)
                formatter.Format(p, verb)
                return
        }
        // Must not touch flags before Formatter looks at them.
        if plus {
                p.fmt.plus = false
        }

        // If we're doing Go syntax and the field knows how to supply it, take care of it now.
        if goSyntax {
                p.fmt.sharp = false
                if stringer, ok := p.field.(GoStringer); ok {
                        wasString = false
                        handled = true
                        defer p.catchPanic(p.field, verb)
                        // Print the result of GoString unadorned.
                        p.fmtString(stringer.GoString(), 's', false)
                        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 wasString and handled, and deferring catchPanic,
                        // must happen before calling the method.
                        switch v := p.field.(type) {
                        case error:
                                wasString = false
                                handled = true
                                defer p.catchPanic(p.field, verb)
                                p.printField(v.Error(), verb, plus, false, depth)
                                return

                        case Stringer:
                                wasString = false
                                handled = true
                                defer p.catchPanic(p.field, verb)
                                p.printField(v.String(), verb, plus, false, depth)
                                return
                        }
                }
        }
        handled = false
        return
}

func (p *pp) printField(field interface{}, verb rune, plus, goSyntax bool, depth int) (wasString bool) {
        if field == nil {
                if verb == 'T' || verb == 'v' {
                        p.buf.Write(nilAngleBytes)
                } else {
                        p.badVerb(verb)
                }
                return false
        }

        p.field = field
        p.value = reflect.Value{}
        // Special processing considerations.
        // %T (the value's type) and %p (its address) are special; we always do them first.
        switch verb {
        case 'T':
                p.printField(reflect.TypeOf(field).String(), 's', false, false, 0)
                return false
        case 'p':
                p.fmtPointer(reflect.ValueOf(field), verb, goSyntax)
                return false
        }

        if wasString, handled := p.handleMethods(verb, plus, goSyntax, depth); handled {
                return wasString
        }

        // Some types can be done without reflection.
        switch f := field.(type) {
        case bool:
                p.fmtBool(f, verb)
        case float32:
                p.fmtFloat32(f, verb)
        case float64:
                p.fmtFloat64(f, verb)
        case complex64:
                p.fmtComplex64(complex64(f), verb)
        case complex128:
                p.fmtComplex128(f, verb)
        case int:
                p.fmtInt64(int64(f), verb)
        case int8:
                p.fmtInt64(int64(f), verb)
        case int16:
                p.fmtInt64(int64(f), verb)
        case int32:
                p.fmtInt64(int64(f), verb)
        case int64:
                p.fmtInt64(f, verb)
        case uint:
                p.fmtUint64(uint64(f), verb, goSyntax)
        case uint8:
                p.fmtUint64(uint64(f), verb, goSyntax)
        case uint16:
                p.fmtUint64(uint64(f), verb, goSyntax)
        case uint32:
                p.fmtUint64(uint64(f), verb, goSyntax)
        case uint64:
                p.fmtUint64(f, verb, goSyntax)
        case uintptr:
                p.fmtUint64(uint64(f), verb, goSyntax)
        case string:
                p.fmtString(f, verb, goSyntax)
                wasString = verb == 's' || verb == 'v'
        case []byte:
                p.fmtBytes(f, verb, goSyntax, depth)
                wasString = verb == 's'
        default:
                // Need to use reflection
                return p.printReflectValue(reflect.ValueOf(field), verb, plus, goSyntax, depth)
        }
        p.field = nil
        return
}

// printValue is like printField but starts with a reflect value, not an interface{} value.
func (p *pp) printValue(value reflect.Value, verb rune, plus, goSyntax bool, depth int) (wasString bool) {
        if !value.IsValid() {
                if verb == 'T' || verb == 'v' {
                        p.buf.Write(nilAngleBytes)
                } else {
                        p.badVerb(verb)
                }
                return false
        }

        // Special processing considerations.
        // %T (the value's type) and %p (its address) are special; we always do them first.
        switch verb {
        case 'T':
                p.printField(value.Type().String(), 's', false, false, 0)
                return false
        case 'p':
                p.fmtPointer(value, verb, goSyntax)
                return false
        }

        // Handle values with special methods.
        // Call always, even when field == nil, because handleMethods clears p.fmt.plus for us.
        p.field = nil // Make sure it's cleared, for safety.
        if value.CanInterface() {
                p.field = value.Interface()
        }
        if wasString, handled := p.handleMethods(verb, plus, goSyntax, depth); handled {
                return wasString
        }

        return p.printReflectValue(value, verb, plus, goSyntax, depth)
}

// printReflectValue is the fallback for both printField and printValue.
// It uses reflect to print the value.
func (p *pp) printReflectValue(value reflect.Value, verb rune, plus, goSyntax bool, depth int) (wasString bool) {
        oldValue := p.value
        p.value = value
BigSwitch:
        switch f := value; f.Kind() {
        case reflect.Bool:
                p.fmtBool(f.Bool(), verb)
        case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
                p.fmtInt64(f.Int(), verb)
        case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
                p.fmtUint64(uint64(f.Uint()), verb, goSyntax)
        case reflect.Float32, reflect.Float64:
                if f.Type().Size() == 4 {
                        p.fmtFloat32(float32(f.Float()), verb)
                } else {
                        p.fmtFloat64(float64(f.Float()), verb)
                }
        case reflect.Complex64, reflect.Complex128:
                if f.Type().Size() == 8 {
                        p.fmtComplex64(complex64(f.Complex()), verb)
                } else {
                        p.fmtComplex128(complex128(f.Complex()), verb)
                }
        case reflect.String:
                p.fmtString(f.String(), verb, goSyntax)
        case reflect.Map:
                if goSyntax {
                        p.buf.WriteString(f.Type().String())
                        if f.IsNil() {
                                p.buf.WriteString("(nil)")
                                break
                        }
                        p.buf.WriteByte('{')
                } else {
                        p.buf.Write(mapBytes)
                }
                keys := f.MapKeys()
                for i, key := range keys {
                        if i > 0 {
                                if goSyntax {
                                        p.buf.Write(commaSpaceBytes)
                                } else {
                                        p.buf.WriteByte(' ')
                                }
                        }
                        p.printValue(key, verb, plus, goSyntax, depth+1)
                        p.buf.WriteByte(':')
                        p.printValue(f.MapIndex(key), verb, plus, goSyntax, depth+1)
                }
                if goSyntax {
                        p.buf.WriteByte('}')
                } else {
                        p.buf.WriteByte(']')
                }
        case reflect.Struct:
                if goSyntax {
                        p.buf.WriteString(value.Type().String())
                }
                p.add('{')
                v := f
                t := v.Type()
                for i := 0; i < v.NumField(); i++ {
                        if i > 0 {
                                if goSyntax {
                                        p.buf.Write(commaSpaceBytes)
                                } else {
                                        p.buf.WriteByte(' ')
                                }
                        }
                        if plus || goSyntax {
                                if f := t.Field(i); f.Name != "" {
                                        p.buf.WriteString(f.Name)
                                        p.buf.WriteByte(':')
                                }
                        }
                        p.printValue(getField(v, i), verb, plus, goSyntax, depth+1)
                }
                p.buf.WriteByte('}')
        case reflect.Interface:
                value := f.Elem()
                if !value.IsValid() {
                        if goSyntax {
                                p.buf.WriteString(f.Type().String())
                                p.buf.Write(nilParenBytes)
                        } else {
                                p.buf.Write(nilAngleBytes)
                        }
                } else {
                        wasString = p.printValue(value, verb, plus, goSyntax, depth+1)
                }
        case reflect.Array, reflect.Slice:
                // Byte slices are special.
                if f.Type().Elem().Kind() == reflect.Uint8 {
                        // We know it's a slice of bytes, but we also know it does not have static type
                        // []byte, or it would have been caught above.  Therefore we cannot convert
                        // it directly in the (slightly) obvious way: f.Interface().([]byte); it doesn't have
                        // that type, and we can't write an expression of the right type and do a
                        // conversion because we don't have a static way to write the right type.
                        // 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, goSyntax, depth)
                        wasString = verb == 's'
                        break
                }
                if goSyntax {
                        p.buf.WriteString(value.Type().String())
                        if f.Kind() == reflect.Slice && f.IsNil() {
                                p.buf.WriteString("(nil)")
                                break
                        }
                        p.buf.WriteByte('{')
                } else {
                        p.buf.WriteByte('[')
                }
                for i := 0; i < f.Len(); i++ {
                        if i > 0 {
                                if goSyntax {
                                        p.buf.Write(commaSpaceBytes)
                                } else {
                                        p.buf.WriteByte(' ')
                                }
                        }
                        p.printValue(f.Index(i), verb, plus, goSyntax, depth+1)
                }
                if goSyntax {
                        p.buf.WriteByte('}')
                } else {
                        p.buf.WriteByte(']')
                }
        case reflect.Ptr:
                v := f.Pointer()
                // pointer to array or slice or struct?  ok at top level
                // but not embedded (avoid loops)
                if v != 0 && depth == 0 {
                        switch a := f.Elem(); a.Kind() {
                        case reflect.Array, reflect.Slice:
                                p.buf.WriteByte('&')
                                p.printValue(a, verb, plus, goSyntax, depth+1)
                                break BigSwitch
                        case reflect.Struct:
                                p.buf.WriteByte('&')
                                p.printValue(a, verb, plus, goSyntax, depth+1)
                                break BigSwitch
                        }
                }
                if goSyntax {
                        p.buf.WriteByte('(')
                        p.buf.WriteString(value.Type().String())
                        p.buf.WriteByte(')')
                        p.buf.WriteByte('(')
                        if v == 0 {
                                p.buf.Write(nilBytes)
                        } else {
                                p.fmt0x64(uint64(v), true)
                        }
                        p.buf.WriteByte(')')
                        break
                }
                if v == 0 {
                        p.buf.Write(nilAngleBytes)
                        break
                }
                p.fmt0x64(uint64(v), true)
        case reflect.Chan, reflect.Func, reflect.UnsafePointer:
                p.fmtPointer(value, verb, goSyntax)
        default:
                p.unknownType(f)
        }
        p.value = oldValue
        return wasString
}

// intFromArg gets the fieldnumth element of a. On return, isInt reports whether the argument has type int.
func intFromArg(a []interface{}, end, i, fieldnum int) (num int, isInt bool, newi, newfieldnum int) {
        newi, newfieldnum = end, fieldnum
        if i < end && fieldnum < len(a) {
                num, isInt = a[fieldnum].(int)
                newi, newfieldnum = i+1, fieldnum+1
        }
        return
}

func (p *pp) doPrintf(format string, a []interface{}) {
        end := len(format)
        fieldnum := 0 // we process one field per non-trivial format
        for i := 0; i < end; {
                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++
                // flags and widths
                p.fmt.clearflags()
        F:
                for ; i < end; i++ {
                        switch format[i] {
                        case '#':
                                p.fmt.sharp = true
                        case '0':
                                p.fmt.zero = true
                        case '+':
                                p.fmt.plus = true
                        case '-':
                                p.fmt.minus = true
                        case ' ':
                                p.fmt.space = true
                        default:
                                break F
                        }
                }
                // do we have width?
                if i < end && format[i] == '*' {
                        p.fmt.wid, p.fmt.widPresent, i, fieldnum = intFromArg(a, end, i, fieldnum)
                        if !p.fmt.widPresent {
                                p.buf.Write(widthBytes)
                        }
                } else {
                        p.fmt.wid, p.fmt.widPresent, i = parsenum(format, i, end)
                }
                // do we have precision?
                if i < end && format[i] == '.' {
                        if format[i+1] == '*' {
                                p.fmt.prec, p.fmt.precPresent, i, fieldnum = intFromArg(a, end, i+1, fieldnum)
                                if !p.fmt.precPresent {
                                        p.buf.Write(precBytes)
                                }
                        } else {
                                p.fmt.prec, p.fmt.precPresent, i = parsenum(format, i+1, end)
                                if !p.fmt.precPresent {
                                        p.fmt.prec = 0
                                        p.fmt.precPresent = true
                                }
                        }
                }
                if i >= end {
                        p.buf.Write(noVerbBytes)
                        continue
                }
                c, w := utf8.DecodeRuneInString(format[i:])
                i += w
                // percent is special - absorbs no operand
                if c == '%' {
                        p.buf.WriteByte('%') // We ignore width and prec.
                        continue
                }
                if fieldnum >= len(a) { // out of operands
                        p.buf.WriteByte('%')
                        p.add(c)
                        p.buf.Write(missingBytes)
                        continue
                }
                field := a[fieldnum]
                fieldnum++

                goSyntax := c == 'v' && p.fmt.sharp
                plus := c == 'v' && p.fmt.plus
                p.printField(field, c, plus, goSyntax, 0)
        }

        if fieldnum < len(a) {
                p.buf.Write(extraBytes)
                for ; fieldnum < len(a); fieldnum++ {
                        field := a[fieldnum]
                        if field != nil {
                                p.buf.WriteString(reflect.TypeOf(field).String())
                                p.buf.WriteByte('=')
                        }
                        p.printField(field, 'v', false, false, 0)
                        if fieldnum+1 < len(a) {
                                p.buf.Write(commaSpaceBytes)
                        }
                }
                p.buf.WriteByte(')')
        }
}

func (p *pp) doPrint(a []interface{}, addspace, addnewline bool) {
        prevString := false
        for fieldnum := 0; fieldnum < len(a); fieldnum++ {
                p.fmt.clearflags()
                // always add spaces if we're doing println
                field := a[fieldnum]
                if fieldnum > 0 {
                        isString := field != nil && reflect.TypeOf(field).Kind() == reflect.String
                        if addspace || !isString && !prevString {
                                p.buf.WriteByte(' ')
                        }
                }
                prevString = p.printField(field, 'v', false, false, 0)
        }
        if addnewline {
                p.buf.WriteByte('\n')
        }
}