2. my Community contribution
Talking
● Networking features
● New 'net' in 1.8
● Reflection
● Channel Internals
● Concurrency with
shared variables
● Working with C code
and plugins
Doing
github.com/golang/go/wiki/Projects
● Lxd
● Juju
● Go-merkle
● Etcd
● Epazote
● Go-kit
● Go-micro
● Prometheus
● llgo
3. outline
● What is Reflection
● Reflection vs Introspection
● 'reflect' package
● Interesting issues
● Packages using reflection
– Protocol encoding (gob)
– Encode-decode model (json, xml)
– template mechanisms
– Tracing
● Dealing uniformly with values of a type
4. Reflection
● the ability of a computer program to
– examine and
– modify its own structure and behavior at runtime.
6. reflect.Type
● A Type represents a golang type.
● It is an interface with multiple methods for
– distinguishing amongst types
– Inspecting the constituent components
● Type descriptors provide information about each
type (it's name and methods)
type Type
func ArrayOf(count int, elem Type) Type
func ChanOf(dir ChanDir, t Type) Type
func FuncOf(in, out []Type, variadic bool) Type
func MapOf(key, elem Type) Type
func PtrTo(t Type) Type
func SliceOf(t Type) Type
func StructOf(fields []StructField) Type
func TypeOf(i interface{}) Type
var w io.Writer
w = os.Stdout
w = new (bytes.Buffer)
w = nil
?
7. reflect.Type
● reflect.TypeOf() accepts any interface{ } and
returns its dynamic type as a reflect.Type
● Note: assignment from concrete value to interface type
performs implicit interface conversion
type ChanDir
func (d ChanDir) String() string
type Kind
func (k Kind) String() string
type Method
type SelectCase
type SelectDir
type SliceHeader
type StringHeader
type StructField
type StructTag
func (tag StructTag) Get(key string) string
func (tag StructTag) Lookup(key string) (value string, ok bool)
8. reflect.Value
type Value
func Append(s Value, x ...Value) Value
func AppendSlice(s, t Value) Value
func Indirect(v Value) Value
func MakeChan(typ Type, buffer int) Value
func MakeFunc(typ Type, fn func(args []Value) (results []Value)) Value
func MakeMap(typ Type) Value
func MakeSlice(typ Type, len, cap int) Value
func New(typ Type) Value
func NewAt(typ Type, p unsafe.Pointer) Value
func ValueOf(i interface{}) Value
func Zero(typ Type) Value
● reflect.Value can hold a value of any type.
● reflect.ValueOf() accepts any interface{} and
returns a reflect.Value containing the interface's
dynamic value (aka concrete value)
9. reflect.Value
type Value
...
func (v Value) Addr() Value
func (v Value) Bool() bool
func (v Value) Bytes() []byte
func (v Value) Call(in []Value) []Value
func (v Value) CallSlice(in []Value) []Value
func (v Value) CanAddr() bool
func (v Value) CanInterface() bool
func (v Value) CanSet() bool
func (v Value) Cap() int
func (v Value) Close()
func (v Value) Complex() complex128
func (v Value) Convert(t Type) Value
func (v Value) Elem() Value
func (v Value) Field(i int) Value
func (v Value) FieldByIndex(index []int) Value
func (v Value) FieldByName(name string) Value
func (v Value) FieldByNameFunc(match func(string) bool) Value
func (v Value) Float() float64
func (v Value) Index(i int) Value
func (v Value) Int() int64
...
10. reflect.Value
type Value
...
func (v Value) Interface() (i interface{})
func (v Value) InterfaceData() [2]uintptr
func (v Value) IsNil() bool
func (v Value) IsValid() bool
func (v Value) Kind() Kind
func (v Value) Len() int
func (v Value) MapIndex(key Value) Value
func (v Value) MapKeys() []Value
func (v Value) Method(i int) Value
func (v Value) MethodByName(name string) Value
func (v Value) NumField() int
func (v Value) NumMethod() int
...
func (v Value) OverflowComplex(x complex128) bool
func (v Value) OverflowFloat(x float64) bool
func (v Value) OverflowInt(x int64) bool
func (v Value) OverflowUint(x uint64) bool
func (v Value) Pointer() uintptr
func (v Value) Recv() (x Value, ok bool)
func (v Value) Send(x Value)
11. reflect.Value
type Value
...
func (v Value) Set(x Value)
func (v Value) SetBool(x bool)
func (v Value) SetBytes(x []byte)
func (v Value) SetCap(n int)
func (v Value) SetComplex(x complex128)
func (v Value) SetFloat(x float64)
func (v Value) SetInt(x int64)
func (v Value) SetLen(n int)
func (v Value) SetMapIndex(key, val Value)
func (v Value) SetPointer(x unsafe.Pointer)
func (v Value) SetString(x string)
func (v Value) SetUint(x uint64)
func (v Value) Slice(i, j int) Value
func (v Value) Slice3(i, j, k int) Value
func (v Value) String() string
func (v Value) TryRecv() (x Value, ok bool)
func (v Value) TrySend(x Value) bool
func (v Value) Type() Type
func (v Value) Uint() uint64
func (v Value) UnsafeAddr() uintptr
12. example show_type
package main
import (
"fmt"
"reflect"
)
func main() {
t := reflect.TypeOf (7)
fmt.Println (t)
fmt.Println (t.String())
}
/* commentary
TypeOf() call assigns the value 7 to the interface{} parameter.
assignment from a concrete value to an interface type performs an implicit conversion
which creates an interface value consisting of two components
. dynamic type (int)
. dynamic value (7)
*/
cf: donovan
13. Example work with interface
package main
import (
"fmt"
"reflect"
"os"
"io"
)
func main() {
var w io.Writer = os.Stdout
fmt.Println (reflect.TypeOf(w))
}
/* commentary
assignment from a concrete value to an interface type performs an implicit conversion
which creates an interface value consisting of two components
. dynamic type os.Stdout
. dynamic value *os.File not io.Writer.
*/
cf: donovan
15. example set the value of a type
package main
import (
"fmt"
"reflect"
)
func main() {
x :=29
xref := reflect.ValueOf(&x).Elem()
px := xref.Addr().Interface().(*int)
*px = 7
fmt.Println(x)
xref.Set (reflect.ValueOf (99))
fmt.Println(x)
}
16. code commentary
/*
commentary
. create addressable value by &x
. return inteface dynamic value reflect.ValueOf(&x)
. Elem() returns the value that the interface v contains or that the pointer v points to.
It panics if v's Kind is not Interface or Ptr. It returns the zero Value if v is nil.
. Addr() returns a value holding a pointer to the variable
. Interface() returns interface{} value containing the pointer
. use type assertion to retrieve the contents of the interface
direct
. use reflect.Value.Set()
*/
17. Some interesting cases
#4876 https://github.com/golang/go/issues/4876
– clarify behavior for unexported names
#5706 https://github.com/golang/go/issues/5706
– field lookup ignores methods that cancel fields
(ambiguity is ignored)
– https://golang.org/src/reflect/type.go#L856
#12918 https://github.com/golang/go/issues/12918
– DeepEqual returns false for equal slices
19. reflection
● Dealing uniformly with values of a type that
– Do not have a common interface
– Do not have a known representation
– Do not exist at the time we design the function
● fmt.Fprintf
20. References {URL}
● S. Feferman (1962), Transfinite Recursions of
Axiomatic Theories, Journal of Symbolic Logic,
27:259-316, 1962.
Conceptual Paper
● Francois Nicola-Demers, Jacques Malenfant
(1995), Reflection in Logic, Functional and
Object-Oriented programming
https://www-master.ufr-info-p6.jussieu
Comparison with CLR model
● Reflection C++/CLI
https://msdn.microsoft.com/en-us/libra
21. References {Golang centric}
● Golang 'reflect' package
https://golang.org/pkg/reflect/
● The Laws of Reflection
https://blog.golang.org/laws-of-reflection
● Russ Cox, Representation of interface values
http://research.swtch.com/2009/12/go-data-structure
● Phil Pearl, Anatomy of function call in Go
https://syslog.ravelin.com/anatomy-of-a-function-cal
●
22. References {json projects}
● easyjson
https://github.com/mailru/easyjson
● ffjson
https://github.com/pquerna/ffjson
● Go lang encoding
https://github.com/golang/go/tree/master/src/encodin
●
23. Legal { Attribution(s) }
The usage of image is purely for illustrative purposes.
The copyright of each image resides with their respective authors.
