Given an arbitrary instance of a struct, I'd like to be able to execute all of its public methods which don't accept arguments.
For example in the code below, I'd like to be able to execute X{}.Foo() and X{}.Bar() without knowing that they exist.
package main
import (
"fmt"
"reflect"
)
type X struct {
Y string
}
func (x X) Foo() string {
return x.Y
}
func (x X) Bar() {
}
func (x X) Baz(q string) {
}
func main() {
fooType := reflect.TypeOf(X{})
for i := 0; i < fooType.NumMethod(); i++ {
method := fooType.Method(i)
fmt.Println(method.Name)
}
}
Change reflect.TypeOf to reflect.ValueOf
Check the type of the Method to ensure that is accepts zero parameters
Call the method with Call
foo := reflect.ValueOf(X{})
for i := 0; i < foo.NumMethod(); i++ {
method := foo.Method(i)
if method.Type().NumIn() == 0 {
method.Call(nil)
}
}
https://play.golang.org/p/KYAfaFlEjVt
Related
Let's say we have a library provide a function Double to double the integer, we use pointer i to get the result value not by return:
package api
type Action interface {
Double(i *int) error
}
type NUM struct{}
func (n NUM) Double(i *int) error {
*i *= 2
return nil
}
in our main function we use this library to do our task. like this:
package app
import (
"fmt"
"github.com/hotsnow/api"
)
func main() {
j := job{a: &api.NUM{}}
d := j.task(3)
fmt.Println(3, d)
}
type job struct {
a api.Action
}
// double me
func (j job) task(i int) int {
j.a.Double(&i)
return i
}
Now we need to test the task() function, how can we get the pointer return bye mock the Double function?
Here is the test:
package app
import (
"github.com/golang/mock/gomock"
"github.com/hotsnow/mocks"
"testing"
)
func TestReq(t *testing.T) {
ctrl := gomock.NewController(t)
defer ctrl.Finish()
m := mocks.NewMockAction(ctrl)
m.EXPECT().Double(gomock.Any()).Return(nil)
j := job{a: m}
got := j.task(3)
if got != 6 {
t.Errorf("got = %#v; want 6", got)
}
}
The code here: https://github.com/hotsnow/mock.git (stackoverflow branch)
you can use gomock setarg function for this
yourPackage.EXPECT().insert(&pointer).SetArg(0, newPointer)
You can achieve this with the provided Eq() matcher, which internally calls reflect.DeepEqual() on the expected and actual values; as per the documentation for this method:
Pointer values are deeply equal if they are equal using Go's == operator or if they point to deeply equal values.
Say we have a function that depends upon an interface method that takes a pointer parameter:
package resource
type ServiceRequest struct {
Name string
Owner *string // this is a pointer so it can be omitted with `nil`
}
type Model struct {
// resource model...
}
type ResourceService interface {
Fetch(req *ServiceRequest) (Model, error)
}
type getResourceHandler struct {
resourceService ResourceService
}
type GetResourceEvent struct {
Resource string
Owner *string
}
func NewResourceHandler(resourceService ResourceService) *getResourceHandler {
return &getResourceHandler{resourceService}
}
func (h *getResourceHandler) Handle(event GetResourceEvent) (Model, error) {
return h.resourceService.Fetch(&ServiceRequest{event.Resource, event.Owner})
}
We can use the Eq() matcher when setting up the expectation against our generated mock of the ResourceService interface:
package test
import (
"testing"
"github.com/golang/mock/gomock"
"github.com/stretchr/testify/assert"
"github.com/org/repo/internal/mock"
"github.com/org/repo/internal/resource"
)
func optionalString(str string) *string {
return &str
}
func Test_GetResourceHandler_ReturnsResultFromService(t *testing.T) {
resourceName := "my-resource"
owner := optionalString("Joe Bloggs")
resourceReq := &resource.ServiceRequest{resourceName, owner}
event := resource.GetResourceEvent{resourceName, owner}
model := resource.Model{ /* fields here... */ }
ctrl := gomock.NewController(t)
mockResourceService := mock.NewMockResourceService(ctrl)
handler := resource.NewResourceHandler(mockResourceService)
mockResourceService.EXPECT().Fetch(gomock.Eq(resourceReq)).Return(model, nil)
res, err := handler.Handle(event)
assert.Nil(t, err)
assert.Equal(t, model, res)
}
If you change the contents of the service request in either the test or the unit under test, you'll see that the test no longer passes. Otherwise, it will pass in spite of the test and the unit under test having their own respective pointers to separate ServiceRequest{} values.
It seems you don't have to use gomock to test the task method.
Since you have an interface, why not just create a mock implementation of the interface, for example:
type dummy struct{
callCount int
}
func (d *dummy) Double(i *int) error {
d.callCount++
return nil
}
d := dummy{}
j := job{a: &d}
got := j.task(3)
if d.callCount != 1 {
// XXX
}
Is there anyway to make a map of function pointers, but functions that take recievers? I know how to do it with regular functions:
package main
func someFunc(x int) int {
return x
}
func main() {
m := make(map[string]func(int)int, 0)
m["1"] = someFunc
print(m["1"](56))
}
But can you do that with functions that take recievers? Something like this (though I've tried this and it doesn't work):
package main
type someStruct struct {
x int
}
func (s someStruct) someFunc() int {
return s.x
}
func main() {
m := make(map[string](someStruct)func()int, 0)
s := someStruct{56}
m["1"] = someFunc
print(s.m["1"]())
}
An obvious work around is to just pass the struct as a parameter, but that's a little dirtier than I would have liked
You can do that using Method Expressions:
https://golang.org/ref/spec#Method_expressions
The call is a bit different, since the method expression takes the receiver as the first argument.
Here's your example modified:
package main
type someStruct struct {
x int
}
func (s someStruct) someFunc() int {
return s.x
}
func main() {
m := make(map[string]func(someStruct)int, 0)
s := someStruct{56}
m["1"] = (someStruct).someFunc
print(m["1"](s))
}
And here's a Go playground for you to test it:
https://play.golang.org/p/PLi5A9of-U
Is it possible get information about caller function in Golang? For example if I have
func foo() {
//Do something
}
func main() {
foo()
}
How can I get that foo has been called from main?
I'm able to this in other language (for example in C# I just need to use CallerMemberName class attribute)
You can use runtime.Caller for easily retrieving information about the caller:
func Caller(skip int) (pc uintptr, file string, line int, ok bool)
Example #1: Print caller file name and line number: https://play.golang.org/p/cdO4Z4ApHS
package main
import (
"fmt"
"runtime"
)
func foo() {
_, file, no, ok := runtime.Caller(1)
if ok {
fmt.Printf("called from %s#%d\n", file, no)
}
}
func main() {
foo()
}
Example #2: Get more information with runtime.FuncForPC: https://play.golang.org/p/y8mpQq2mAv
package main
import (
"fmt"
"runtime"
)
func foo() {
pc, _, _, ok := runtime.Caller(1)
details := runtime.FuncForPC(pc)
if ok && details != nil {
fmt.Printf("called from %s\n", details.Name())
}
}
func main() {
foo()
}
expanding on my comment, here's some code that returns the current func's caller
import(
"fmt"
"runtime"
)
func getFrame(skipFrames int) runtime.Frame {
// We need the frame at index skipFrames+2, since we never want runtime.Callers and getFrame
targetFrameIndex := skipFrames + 2
// Set size to targetFrameIndex+2 to ensure we have room for one more caller than we need
programCounters := make([]uintptr, targetFrameIndex+2)
n := runtime.Callers(0, programCounters)
frame := runtime.Frame{Function: "unknown"}
if n > 0 {
frames := runtime.CallersFrames(programCounters[:n])
for more, frameIndex := true, 0; more && frameIndex <= targetFrameIndex; frameIndex++ {
var frameCandidate runtime.Frame
frameCandidate, more = frames.Next()
if frameIndex == targetFrameIndex {
frame = frameCandidate
}
}
}
return frame
}
// MyCaller returns the caller of the function that called it :)
func MyCaller() string {
// Skip GetCallerFunctionName and the function to get the caller of
return getFrame(2).Function
}
// foo calls MyCaller
func foo() {
fmt.Println(MyCaller())
}
// bar is what we want to see in the output - it is our "caller"
func bar() {
foo()
}
func main(){
bar()
}
For more examples: https://play.golang.org/p/cv-SpkvexuM
What is the way of printing "Foo" here? In this example, what prints is "string".
http://play.golang.org/p/ZnK6PRwEPp
type A struct {
Foo string
}
func (a *A) PrintFoo() {
fmt.Println("Foo value is " + a.Foo)
}
func main() {
a := &A{Foo: "afoo"}
val := reflect.Indirect(reflect.ValueOf(a))
fmt.Println(val.Field(0).Type().Name())
}
You want val.Type().Field(0).Name. The Field method on reflect.Type will return a struct describing that field, which includes the name, among other information.
There is no way to retrieve the field name for a reflect.Value representing a particular field value, since that is a property of the containing struct.
I think the better way to get the fields' name in the struct is
func main() {
a := &A{Foo: "afoo"}
val := reflect.ValueOf(a).Elem()
for i:=0; i<val.NumField();i++{
fmt.Println(val.Type().Field(i).Name)
}
}
There are two tips:
use .Elem() after you reflect.ValueOf(a), because in your case, a is a pointer.
val.Field(i).Type().Name is totally different from val.Type().Field(i).Name. The latter one can get the name of the field in the struct
Hope that it is helpful..
If you want to have a look at more cases, please check my 2mins article
You need to Get the Field of the Type Definition not of the Value.
http://play.golang.org/p/7Bc7MJikbJ
package main
import "fmt"
import "reflect"
type A struct {
Foo string
}
func (a *A) PrintFoo() {
fmt.Println("Foo value is " + a.Foo)
}
func main() {
a := &A{Foo: "afoo"}
val := reflect.Indirect(reflect.ValueOf(a))
fmt.Println(val.Type().Field(0).Name)
}
With the new Names method of the structs package it's even more easier:
package main
import (
"fmt"
"github.com/fatih/structs"
)
type A struct {
Foo string
Bar int
}
func main() {
names := structs.Names(&A{})
fmt.Println(names) // ["Foo", "Bar"]
}
You can also use https://github.com/fatih/structs
// Convert the fields of a struct to a []*Field
fields := s.Fields()
for _, f := range fields {
fmt.Printf("field name: %+v\n", f.Name())
}
package main
import "fmt"
import "reflect"
type A struct {
Foo string
}
func (a *A) PrintFoo() {
fmt.Println("Foo value is " + a.Foo)
}
func main() {
a := &A{Foo: "afoo"}
//long and bored code
t := reflect.TypeOf(*a)
if t.Kind() == reflect.Struct {
for i := 0; i < t.NumField(); i++ {
fmt.Println(t.Field(i).Name)
}
} else {
fmt.Println("not a stuct")
}
//shorthanded call
fmt.Println(reflect.TypeOf(*a).Field(0).Name)//can panic if no field exists
}
You can use this function, which takes the struct as the first parameter, and then its fields. It returns the map type, which is convenient to use
If you use fields from another structure, nothing will happen
If you try to use a different type, it will cause panic
Note that the field has an ordinal number according to the list (starting from 0). All fields in the structure must start with uppercase
func GetStructFieldName(Struct interface{}, StructField ...interface{}) (fields map[int]string) {
fields = make(map[int]string)
s := reflect.ValueOf(Struct).Elem()
for r := range StructField {
f := reflect.ValueOf(StructField[r]).Elem()
for i := 0; i < s.NumField(); i++ {
valueField := s.Field(i)
if valueField.Addr().Interface() == f.Addr().Interface() {
fields[i] = s.Type().Field(i).Name
}
}
}
return fields
}
Full example and playground
package main
import (
"fmt"
"reflect"
)
type Example struct {
Apple bool
Pear int
}
func GetStructFieldName(Struct interface{}, StructField ...interface{}) (fields map[int]string) {
fields = make(map[int]string)
for r := range StructField {
s := reflect.ValueOf(Struct).Elem()
f := reflect.ValueOf(StructField[r]).Elem()
for i := 0; i < s.NumField(); i++ {
valueField := s.Field(i)
if valueField.Addr().Interface() == f.Addr().Interface() {
fields[i] = s.Type().Field(i).Name
}
}
}
return fields
}
func main() {
e := Example{}
names := GetStructFieldName(&e, &e.Apple, &e.Pear)
fmt.Println(names)
fmt.Println(names[0], names[1])
for i := range names {
fmt.Println(names[i])
}
/* Output:
map[0:Apple 1:Pear]
Apple Pear
Apple
Pear
*/
}
I am looking for help understanding how to access struct fields that are inside a container.vector.Vector.
The following code:
package main
import "fmt"
import "container/vector"
func main() {
type Hdr struct {
H string
}
type Blk struct {
B string
}
a := new(vector.Vector)
a.Push(Hdr{"Header_1"})
a.Push(Blk{"Block_1"})
for i := 0; i < a.Len(); i++ {
fmt.Printf("a.At(%d) == %+v\n", i, a.At(i))
x := a.At(i)
fmt.Printf("%+v\n", x.H)
}
}
Produces the error prog.go:22: x.H undefined (type interface { } has no field or method H)
removing lines 21 and 22 produces:
a.At(0) == {H:Header_1}
a.At(1) == {B:Block_1}
So, how exactly does one access 'H' or 'B'? It seems like I need to convert those interfaces to structs, but... I dunno. I'm at a loss.
Thanks for any help.
Use a Go type switch or type assertion to distinguish between the Hdr and Blk types. For example,
package main
import (
"fmt"
"container/vector"
)
func main() {
type Hdr struct {
H string
}
type Blk struct {
B string
}
a := new(vector.Vector)
a.Push(Hdr{"Header_1"})
a.Push(Blk{"Block_1"})
for i := 0; i < a.Len(); i++ {
fmt.Printf("a.At(%d) == %+v\n", i, a.At(i))
x := a.At(i)
switch x := x.(type) {
case Hdr:
fmt.Printf("%+v\n", x.H)
case Blk:
fmt.Printf("%+v\n", x.B)
}
}
}
However, effective the weekly.2011-10-18 release:
The container/vector package has been deleted. Slices are better:
SliceTricks.
Therefore, for the latest releases,
package main
import "fmt"
func main() {
type Hdr struct {
H string
}
type Blk struct {
B string
}
var a []interface{}
a = append(a, Hdr{"Header_1"})
a = append(a, Blk{"Block_1"})
for i := 0; i < len(a); i++ {
fmt.Printf("a[%d]) == %+v\n", i, a[i])
x := a[i]
switch x := x.(type) {
case Hdr:
fmt.Printf("%+v\n", x.H)
case Blk:
fmt.Printf("%+v\n", x.B)
}
}
}