// Package repr attempts to represent Go values in a form that can be copy-and-pasted into source
// code directly.
//
// Some values (such as pointers to basic types) can not be represented directly in
// Go. These values will be output as `&<value>`. eg. `&23`
package repr
import (
"bytes"
"fmt"
"io"
"os"
"reflect"
"sort"
"time"
"unsafe"
)
var (
// "Real" names of basic kinds, used to differentiate type aliases.
realKindName = map[reflect.Kind]string{
reflect.Bool: "bool",
reflect.Int: "int",
reflect.Int8: "int8",
reflect.Int16: "int16",
reflect.Int32: "int32",
reflect.Int64: "int64",
reflect.Uint: "uint",
reflect.Uint8: "uint8",
reflect.Uint16: "uint16",
reflect.Uint32: "uint32",
reflect.Uint64: "uint64",
reflect.Uintptr: "uintptr",
reflect.Float32: "float32",
reflect.Float64: "float64",
reflect.Complex64: "complex64",
reflect.Complex128: "complex128",
reflect.Array: "array",
reflect.Chan: "chan",
reflect.Func: "func",
reflect.Map: "map",
reflect.Slice: "slice",
reflect.String: "string",
}
goStringerType = reflect.TypeOf((*fmt.GoStringer)(nil)).Elem()
byteSliceType = reflect.TypeOf([]byte{})
)
// Default prints to os.Stdout with two space indentation.
var Default = New(os.Stdout, Indent(" "))
// An Option modifies the default behaviour of a Printer.
type Option func(o *Printer)
// Indent output by this much.
func Indent(indent string) Option { return func(o *Printer) { o.indent = indent } }
// NoIndent disables indenting.
func NoIndent() Option { return Indent("") }
// OmitEmpty sets whether empty field members should be omitted from output.
func OmitEmpty(omitEmpty bool) Option { return func(o *Printer) { o.omitEmpty = omitEmpty } }
// ExplicitTypes adds explicit typing to slice and map struct values that would normally be inferred by Go.
func ExplicitTypes(ok bool) Option { return func(o *Printer) { o.explicitTypes = true } }
// IgnoreGoStringer disables use of the .GoString() method.
func IgnoreGoStringer() Option { return func(o *Printer) { o.ignoreGoStringer = true } }
// Hide excludes the given types from representation, instead just printing the name of the type.
func Hide(ts ...interface{}) Option {
return func(o *Printer) {
for _, t := range ts {
rt := reflect.Indirect(reflect.ValueOf(t)).Type()
o.exclude[rt] = true
}
}
}
// AlwaysIncludeType always includes explicit type information for each item.
func AlwaysIncludeType() Option { return func(o *Printer) { o.alwaysIncludeType = true } }
// Printer represents structs in a printable manner.
type Printer struct {
indent string
omitEmpty bool
ignoreGoStringer bool
alwaysIncludeType bool
explicitTypes bool
exclude map[reflect.Type]bool
w io.Writer
}
// New creates a new Printer on w with the given Options.
func New(w io.Writer, options ...Option) *Printer {
p := &Printer{
w: w,
indent: " ",
omitEmpty: true,
exclude: map[reflect.Type]bool{},
}
for _, option := range options {
option(p)
}
return p
}
func (p *Printer) nextIndent(indent string) string {
if p.indent != "" {
return indent + p.indent
}
return ""
}
func (p *Printer) thisIndent(indent string) string {
if p.indent != "" {
return indent
}
return ""
}
// Print the values.
func (p *Printer) Print(vs ...interface{}) {
for i, v := range vs {
if i > 0 {
fmt.Fprint(p.w, " ")
}
p.reprValue(map[reflect.Value]bool{}, reflect.ValueOf(v), "", true)
}
}
// Println prints each value on a new line.
func (p *Printer) Println(vs ...interface{}) {
for i, v := range vs {
if i > 0 {
fmt.Fprint(p.w, " ")
}
p.reprValue(map[reflect.Value]bool{}, reflect.ValueOf(v), "", true)
}
fmt.Fprintln(p.w)
}
func (p *Printer) reprValue(seen map[reflect.Value]bool, v reflect.Value, indent string, showType bool) { // nolint: gocyclo
if seen[v] {
fmt.Fprint(p.w, "...")
return
}
seen[v] = true
defer delete(seen, v)
if v.Kind() == reflect.Invalid || (v.Kind() == reflect.Ptr || v.Kind() == reflect.Map || v.Kind() == reflect.Chan || v.Kind() == reflect.Slice || v.Kind() == reflect.Func || v.Kind() == reflect.Interface) && v.IsNil() {
fmt.Fprint(p.w, "nil")
return
}
if p.exclude[v.Type()] {
fmt.Fprintf(p.w, "%s...", v.Type().Name())
return
}
t := v.Type()
if t == byteSliceType {
fmt.Fprintf(p.w, "[]byte(%q)", v.Bytes())
return
}
// If we can't access a private field directly with reflection, try and do so via unsafe.
if !v.CanInterface() && v.CanAddr() {
uv := reflect.NewAt(t, unsafe.Pointer(v.UnsafeAddr())).Elem()
if uv.CanInterface() {
v = uv
}
}
// Attempt to use fmt.GoStringer interface.
if !p.ignoreGoStringer && t.Implements(goStringerType) {
fmt.Fprint(p.w, v.Interface().(fmt.GoStringer).GoString())
return
}
in := p.thisIndent(indent)
ni := p.nextIndent(indent)
switch v.Kind() {
case reflect.Slice, reflect.Array:
fmt.Fprintf(p.w, "%s{", v.Type())
if v.Len() == 0 {
fmt.Fprint(p.w, "}")
} else {
if p.indent != "" {
fmt.Fprintf(p.w, "\n")
}
for i := 0; i < v.Len(); i++ {
e := v.Index(i)
fmt.Fprintf(p.w, "%s", ni)
p.reprValue(seen, e, ni, p.alwaysIncludeType || p.explicitTypes)
if p.indent != "" {
fmt.Fprintf(p.w, ",\n")
} else if i < v.Len()-1 {
fmt.Fprintf(p.w, ", ")
}
}
fmt.Fprintf(p.w, "%s}", in)
}
case reflect.Chan:
fmt.Fprintf(p.w, "make(")
fmt.Fprintf(p.w, "%s", v.Type())
fmt.Fprintf(p.w, ", %d)", v.Cap())
case reflect.Map:
fmt.Fprintf(p.w, "%s{", v.Type())
if p.indent != "" && v.Len() != 0 {
fmt.Fprintf(p.w, "\n")
}
keys := v.MapKeys()
sort.Slice(keys, func(i, j int) bool {
return fmt.Sprint(keys[i]) < fmt.Sprint(keys[j])
})
for i, k := range keys {
kv := v.MapIndex(k)
fmt.Fprintf(p.w, "%s", ni)
p.reprValue(seen, k, ni, p.alwaysIncludeType || p.explicitTypes)
fmt.Fprintf(p.w, ": ")
p.reprValue(seen, kv, ni, true)
if p.indent != "" {
fmt.Fprintf(p.w, ",\n")
} else if i < v.Len()-1 {
fmt.Fprintf(p.w, ", ")
}
}
fmt.Fprintf(p.w, "%s}", in)
case reflect.Struct:
if td, ok := v.Interface().(time.Time); ok {
timeToGo(p.w, td)
} else {
if showType {
fmt.Fprintf(p.w, "%s{", v.Type())
} else {
fmt.Fprint(p.w, "{")
}
if p.indent != "" && v.NumField() != 0 {
fmt.Fprintf(p.w, "\n")
}
for i := 0; i < v.NumField(); i++ {
t := v.Type().Field(i)
f := v.Field(i)
if p.omitEmpty && isZero(f) {
continue
}
fmt.Fprintf(p.w, "%s%s: ", ni, t.Name)
p.reprValue(seen, f, ni, true)
if p.indent != "" {
fmt.Fprintf(p.w, ",\n")
} else if i < v.NumField()-1 {
fmt.Fprintf(p.w, ", ")
}
}
fmt.Fprintf(p.w, "%s}", indent)
}
case reflect.Ptr:
if v.IsNil() {
fmt.Fprintf(p.w, "nil")
return
}
if showType {
fmt.Fprintf(p.w, "&")
}
p.reprValue(seen, v.Elem(), indent, showType)
case reflect.String:
if t.Name() != "string" || p.alwaysIncludeType {
fmt.Fprintf(p.w, "%s(%q)", t, v.String())
} else {
fmt.Fprintf(p.w, "%q", v.String())
}
case reflect.Interface:
if v.IsNil() {
fmt.Fprintf(p.w, "interface {}(nil)")
} else {
p.reprValue(seen, v.Elem(), indent, true)
}
default:
if t.Name() != realKindName[t.Kind()] || p.alwaysIncludeType {
fmt.Fprintf(p.w, "%s(%v)", t, v)
} else {
fmt.Fprintf(p.w, "%v", v)
}
}
}
// String returns a string representing v.
func String(v interface{}, options ...Option) string {
w := bytes.NewBuffer(nil)
options = append([]Option{NoIndent()}, options...)
p := New(w, options...)
p.Print(v)
return w.String()
}
func extractOptions(vs ...interface{}) (args []interface{}, options []Option) {
for _, v := range vs {
if o, ok := v.(Option); ok {
options = append(options, o)
} else {
args = append(args, v)
}
}
return
}
// Println prints v to os.Stdout, one per line.
func Println(vs ...interface{}) {
args, options := extractOptions(vs...)
New(os.Stdout, options...).Println(args...)
}
// Print writes a representation of v to os.Stdout, separated by spaces.
func Print(vs ...interface{}) {
args, options := extractOptions(vs...)
New(os.Stdout, options...).Print(args...)
}
func isZero(v reflect.Value) bool {
switch v.Kind() {
case reflect.Array, reflect.String:
return v.Len() == 0
case reflect.Bool:
return !v.Bool()
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
return v.Int() == 0
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
return v.Uint() == 0
case reflect.Float32, reflect.Float64:
return v.Float() == 0
case reflect.Interface, reflect.Map, reflect.Ptr, reflect.Slice:
return v.IsNil()
}
return false
}
func timeToGo(w io.Writer, t time.Time) {
if t.IsZero() {
fmt.Fprint(w, "time.Time{}")
return
}
var zone string
switch loc := t.Location(); loc {
case nil:
zone = "nil"
case time.UTC:
zone = "time.UTC"
case time.Local:
zone = "time.Local"
default:
n, off := t.Zone()
zone = fmt.Sprintf("time.FixedZone(%q, %d)", n, off)
}
y, m, d := t.Date()
fmt.Fprintf(w, `time.Date(%d, %d, %d, %d, %d, %d, %d, %s)`, y, m, d, t.Hour(), t.Minute(), t.Second(), t.Nanosecond(), zone)
}