How does I check if a type implement an interface?
gnu.bash
example:
type iface interface {
bla()
}
type inty int
func (i *inty) bla() {
}
I need a something like
func CheckForInterface(object, interface) bool
thanks for help, aotto1968
jimt
if ok := inty.(iface); ok {
yay()
jimmy frasche
Type assertions go the other way.
You could write a CheckForInterface function with the reflection
package, I suppose. But I don't see the utility.
chris dollin
> Hi,
>
> example:
>
> type iface interface {
> bla()
> }
>
> type inty int
>
> func (i *inty) bla() {
> }
>
> I need a something like
>
> func CheckForInterface(object, interface) bool
jimt has mentioned using type assertions, but I'd be interested
to know what you're trying to do with this check.
Chris
--
Chris "allusive" Dollin
gnu.bash
===========================================
package gomsgque
type IServerSetup interface {
ServerSetup() MqSException
}
===========================================
package main
type Server struct {
*gomsgque.MqS
}
func NewServer() *Server {
//fmt.Println("NewServer...")
ret := &Server{gomsgque.NewMqS()}
//ret.ConfigServerSetup()
return ret
}
func (this *Server) ServerSetup() gomsgque.MqSException {
var ret gomsgque.MqSException
return ret
}
func main() {
var srv = NewServer()
defer srv.Exit("END")
fmt.Println("val = ", reflect.Typeof(srv))
fmt.Println("val = ", Server.(gomsgque.IServerSetup))
}
=> server.go:45: type Server is not an expression
using the pointer object "srv"
func main() {
var srv = NewServer()
defer srv.Exit("END")
fmt.Println("val = ", reflect.Typeof(srv))
fmt.Println("val = ", srv.(gomsgque.IServerSetup))
}
=> server.go:45: invalid type assertion: srv.(gomsgque.IServerSetup)
(non-interface type *Server on left)
using the object "*srv"
func main() {
var srv = NewServer()
defer srv.Exit("END")
fmt.Println("val = ", reflect.Typeof(srv))
fmt.Println("val = ", (*srv).(gomsgque.IServerSetup))
}
=> server.go:45: invalid type assertion: *srv.(gomsgque.IServerSetup)
(non-interface type Server on left)
is an other option available ?
gnu.bash
I come from c++/java/c# and the behavior of an object changes
depending on the
interfaces implemented
example c++ =================================
void MqC::Init () {
...
// init the server interface
IServerSetup * const iSetup =
dynamic_cast<IServerSetup*const>(this);
if (iSetup != NULL) {
struct ProcCallS * ptr = (struct ProcCallS *)
MqSysMalloc(MQ_ERROR_PANIC, sizeof(*ptr));
ptr->type = ProcCallS::PC_IServerSetup;
ptr->call.ServerSetup = iSetup;
MqConfigSetServerSetup (&context, ProcCall,
static_cast<MQ_PTR>(ptr), ProcFree, NULL);
}
....
JAVA
JNIEXPORT void JNICALL NS(ContextCreate) (
JNIEnv *env,
jobject self
)
{
...
// check for Server
if ((*env)->IsInstanceOf(env, self, NS(Class_IServerSetup)) ==
JNI_TRUE) {
ErrorMqToJavaWithCheck (NS(ProcCreate)(context, self, NULL,
NS(MID_IServerSetup_ServerSetup), NULL, &call));
MqConfigSetServerSetup (context, NS(ProcCall), call, NS(ProcFree),
NS(ProcCopy));
}
C#
public MqS() {
...
if (this is IServerSetup) {
MqConfigSetServerSetup (context, fProcCall, (IntPtr)
GCHandle.Alloc(
new ProcData((Callback)((IServerSetup) this).ServerSetup)),
fProcFree, IntPtr.Zero);
}
...
mfg, Andreas Otto
chris dollin
> is an other option available ?
What are you trying to /do/?
In:
<<<<<<<
func main() {
var srv = NewServer()
defer srv.Exit("END")
fmt.Println("val = ", reflect.Typeof(srv))
fmt.Println("val = ", (*srv).(gomsgque.IServerSetup))
}
>>>>>>>
you are trying to print out a type representation for srv.
(You could use %T, which would be a lot nicer than
doing the reflect by hand.) But you /know/ what the
type of srv is: it's the type returned by NewServer, which
is *Server.
You can't type-test a non-interface type but you can
an interface type; so try
fmt.Println("val = ", interface{}(srv).(gomsgque.IServerSetup))
The `interface{}(s)` is a cast of srv to the type interface{},
which you can now apply the type-check to.
chris dollin
> Hi,
>
> I come from c++/java/c# and the behavior of an object changes
> depending on the
> interfaces implemented
Different interfaces expose different behaviours, yes.
> JAVA
>
> JNIEXPORT void JNICALL NS(ContextCreate) (
> JNIEnv *env,
> jobject self
> )
> {
> ...
> // check for Server
> if ((*env)->IsInstanceOf(env, self, NS(Class_IServerSetup)) ==
> JNI_TRUE) {
> ErrorMqToJavaWithCheck (NS(ProcCreate)(context, self, NULL,
> NS(MID_IServerSetup_ServerSetup), NULL, &call));
> MqConfigSetServerSetup (context, NS(ProcCall), call, NS(ProcFree),
> NS(ProcCopy));
> }
That's not Java.
roger peppe
by simply assigning to a variable of the required interface
type. the compiler will tell you if it does not implement the
interface.
On 16 November 2010 18:48, gnu.bash <aott...@t-online.de> wrote:
jimmy frasche
its type, you can use a type switch.
Jessta
> I need a something like
>
> func CheckForInterface(object, interface) bool
>
There is no reason to need to know what interfaces a type satisfies at runtime.
You just make an interface for the behaviour your function requires
and the compiler will tell you if the types you're passing in satisfy
that interface.
- jessta
--
=====================
http://jessta.id.au
gnu.bash
the type print out is just for testing.
I want to bind an external library to GO and I use Interfaces
modify the behavior.
For example JAVA
final class Server extends MqS implements IServerSetup, ...... {
public void ServerSetup() throws MqSException {
....
}
}
during setup (using JNI) I check if the interface is available ...
JNIEXPORT void JNICALL NS(ContextCreate) (
JNIEnv *env,
jobject self
)
{
JNI_TRUE) {
ErrorMqToJavaWithCheck (NS(ProcCreate)(context, self, NULL,
NS(MID_IServerSetup_ServerSetup), NULL, &call));
MqConfigSetServerSetup (context, NS(ProcCall), call, NS(ProcFree),
NS(ProcCopy));
}
}
and if YES is call my own C code to call this Interface function. In
this case the code behave as Server and
use the "ServerSetup" method to configure the server.
Every language supporting interfaces support a function like
"IsInstanceOf" in Java to check for the
availability of this interface
the Println code from down is just for testing
mfg, aotto1968
On 16 Nov., 20:55, chris dollin <ehog.he...@googlemail.com> wrote:
gnu.bash
this is JNI, I post a full JAVA example above
andrey mirtchovski
MID_IServerSetup_ServerSetup just blows my mind!
chris dollin
> Every language supporting interfaces support a function like
> "IsInstanceOf" in Java to check for the
> availability of this interface
And indeed you can do this in Go, as the message from me you quoted:
>> You can't type-test a non-interface type but you can
>> an interface type; so try
>>
>> fmt.Println("val = ", interface{}(srv).(gomsgque.IServerSetup))
>>
>> The `interface{}(s)` is a cast of srv to the type interface{},
>> which you can now apply the type-check to.
points out.
gnu.bash
I found a temporary solution
1. gomsgque =====================================
func (this *MqS) ConfigSetServerSetup(ifc IServerSetup) {
C.MqConfigSetServerSetup(this.ctx, nil, nil, nil, nil)
}
func (this *MqS) ConfigSetServerCleanup(ifc IServerCleanup) {
C.MqConfigSetServerCleanup(this.ctx, nil, nil, nil, nil)
}
2. main =========================================
*gomsgque.MqS
}
func NewServer() *Server {
ret := &Server{gomsgque.NewMqS()}
ret.ConfigSetServerCleanup(ret)
//ret.ConfigServerSetup()
return ret
}
// //export ServerSetup
var ret gomsgque.MqSException
return ret
}
var srv = NewServer()
defer srv.Exit("END")
}
the compiler *complain* about missing interface "ServerCleanup"
but you still have the "double (ret)" coding...
ret.ConfigSetServerSetup(ret)
The problem is the "embedded" object "MqS"
the first "ret" will be the "MqS->this" and the second "ret" will be
the "Server->this"
mfg, Andreas Otto (aotto1968)
gnu.bash
I do the following check ....
func main() {
var srv = NewServer()
defer srv.Exit("END")
}
IServerSetup is "implemented" and IServerCleanup is *not*
"implemented"
and this is the solution ....
> ./server
NewServer...
val = *main.Server
val = &{0x7f47dd97f0f0}
the code stops after the first println
mfg, andreas otto
chris dollin
My mistake.
What I should have added was that to /test/ whether some interface
value V can be used as some type T, you need to use a type-testing
assignment (or declaration):
someT, isT := V.(T)
[or its big brother, the type switch)]
which will set isT to true if V can work as a T and someT to the T-shaped
value for V.
Using V.(T) as a single expression will deliver the T-value of V if
possible but otherwise panic.
jimmy frasche
if s, ok := x.(ServerSetup); ok {
return s.ServerSetup()
}
return nil
}
and similiarly for the cleanup. Do not prepend an I to your interface names.
gnu.bash
now the "inline" test is working as well ....
func main() {
var srv = NewServer()
defer srv.Exit("END")
fmt.Printf("val = %T\n", srv)
fmt.Printf("val = has gomsgque.IServerSetup -> %T\n", s)
}
if s, ok := interface{}(srv).(gomsgque.IServerCleanup); ok {
fmt.Printf("val = has gomsgque.IServerCleanup -> %T\n", s)
}
fmt.Println("END")
}
wit the result ....
NewServer...
val = *main.Server
val = has gomsgque.IServerSetup -> *main.Server
END
=> this is right .... well done
some thing left over .... if I use the code ...
var srv = NewServer()
defer srv.Exit("END")
fmt.Printf("val = %T\n", srv)
fmt.Printf("val = has gomsgque.IServerSetup -> \n")
}
if s, ok := interface{}(srv).(gomsgque.IServerCleanup); ok {
fmt.Printf("val = has gomsgque.IServerCleanup -> \n")
}
fmt.Println("END")
}
... without reusing the variable "s" ... i get an compiler error ...
server.go:47: s declared and not used
server.go:50: s declared and not used
make: *** [server] Fehler 1
... to solve this I have to use the "_" dummy variable ....
thanks to everybody ....
mfg, Andreas Otto