Re: How to dispatch a class function for an object accessed by handle?
On Friday, 6 March 2020 at 15:19:39 UTC, Adam D. Ruppe wrote: On Friday, 6 March 2020 at 15:05:56 UTC, wjoe wrote: But didn't like the string part and that's when I introduced the alias fn because I figured maybe it's possible to do something like: factory.dispatch!(Bitmap.load)(handle, path); and get the Bitmap part from that alias and hence save the duplicate Bitmap type in factory.dispatch!(Bitmap, Bitmap.load)(...); ooh you can do that. on the alias, use __traits(identifier) to get thef ucntion name and __traits(parent) to get the class name! then it reduces to what we already wrote. Awesome! I read the docs up and down but I couldn't figure it out. Thank you!
Re: How to dispatch a class function for an object accessed by handle?
On Friday, 6 March 2020 at 15:05:56 UTC, wjoe wrote: But didn't like the string part and that's when I introduced the alias fn because I figured maybe it's possible to do something like: factory.dispatch!(Bitmap.load)(handle, path); and get the Bitmap part from that alias and hence save the duplicate Bitmap type in factory.dispatch!(Bitmap, Bitmap.load)(...); ooh you can do that. on the alias, use __traits(identifier) to get thef ucntion name and __traits(parent) to get the class name! then it reduces to what we already wrote.
Re: How to dispatch a class function for an object accessed by handle?
On Friday, 6 March 2020 at 14:14:04 UTC, Adam D. Ruppe wrote:
On Friday, 6 March 2020 at 14:05:55 UTC, Steven Schveighoffer
wrote:
Adam's way doesn't work either, because the call doesn't use
the alias, but just instantiates opDispatch with the new name!'
oh yikes, how did I not notice that?!
so yeah just kinda screwed. I'd probably suggest at tis point
having the opDispatch be a trivial implementation that just
forwards to another named method.
struct A {
template opDispatch(string name) {
auto opDispatch(T, Args...)(Args args) {
return other_name!(name, T, Args)(args);
}
}
auto other_name(string name, T, Args...)(Args args) {
// real implementation
}
}
and then to test it externally you do
a.other_name!("whatever", Bitmap)(args, here);
This isn't the worst thing to use and since it's just for testing
it's fine.
I came up with a similar interface like a.other_name!("whatever",
Bitmap)(args, here); after discarding .opDispatch() and I called
the thing
.dispatch(T, string fn, ARGS...)(...).
But didn't like the string part and that's when I introduced the
alias fn because I figured maybe it's possible to do something
like:
factory.dispatch!(Bitmap.load)(handle, path);
and get the Bitmap part from that alias and hence save the
duplicate Bitmap type in factory.dispatch!(Bitmap,
Bitmap.load)(...);
Anyways thanks for your help.
Re: How to dispatch a class function for an object accessed by handle?
On Friday, 6 March 2020 at 13:55:25 UTC, Steven Schveighoffer
wrote:
On 3/6/20 6:51 AM, wjoe wrote:
On Thursday, 5 March 2020 at 18:33:41 UTC, Adam D. Ruppe wrote:
On Thursday, 5 March 2020 at 14:24:33 UTC, wjoe wrote:
[...]
template opDispatch(string name) {
auto opDispatch(T, Args...)(Args args) {
...
}
}
[...]
NOTE: opDispatch suppresses internal compile errors, it will
just say "no such property whatever". you can explicitly
instantiate with `f.opDispatch!"whatever` to help see better
errors.
Follow-up question:
Calling f.whatever!SomeResource(...); works no problem.
However I can't figure out how to call a function by
explicitly instantiating opDispatch.
Since f.opDispatch!"load"(handle, "wallpaper.png");
doesn't compile, I refreshed my memory about the shortcut
syntax and the eponymous syntax and the way I read it is that
this is a template of a template.
So I tried this: f.opDispatch!"load".opDispatch!Bitmap(handle,
"path/to/wallpaper.png");
This doesn't work, because an eponymous template does not
provide access to the internals of the template.
But this doesn't compile either and errors out with:
Error: Cannot resolve type for f.opDispatch(T,
ARGS...)(ResourceHandle handle, ARGS args)
I don't understand this error message. Which type can't be
resolved?
Is there a way to look at output of what the compiler
generates for f.whatever!SomeResource(...); ?
You can use -vcg-ast, but this isn't necessarily going to be
compilable code.
D doesn't allow chained instantiation (i.e. (A!B)!C), so you
need to use either a mixin or a helper:
import std.meta;
enum fname = "load";
Instantiate!(f.opDispatch!fname,
Bitmap)("path/to/wallpaper.png")
or
mixin("f." ~ fname ~ "!(Bitmap)(...);");
I'm assuming fname is given to you as a compile-time string and
that's why you'd need to run opDispatch manually.
-Steve
I tried Instantiate this morning after I found a reply you made
to someone else who was trying to chain instantiate. But for the
reason you stated it didn't work.
Funny you mention: mixin("f." ~ fname ~ "!(Bitmap)(...);");
Because that's like my initial implementation :)
As for the the command line switch. My plan wasn't to copy paste.
Sometimes I have a hard time to comprehend results because it's
like I've put water, flour and eggs on the table. Then I'm
presented with a loaf of bread and I'm baffled. Then I want to
understand what happened between putting the ingredients on the
table and the ready baked loaf.
Anyways, thanks for your answers.
Re: How to dispatch a class function for an object accessed by handle?
On 3/6/20 9:14 AM, Adam D. Ruppe wrote:
On Friday, 6 March 2020 at 14:05:55 UTC, Steven Schveighoffer wrote:
Adam's way doesn't work either, because the call doesn't use the
alias, but just instantiates opDispatch with the new name!'
oh yikes, how did I not notice that?!
so yeah just kinda screwed. I'd probably suggest at tis point having the
opDispatch be a trivial implementation that just forwards to another
named method.
struct A {
template opDispatch(string name) {
auto opDispatch(T, Args...)(Args args) {
return other_name!(name, T, Args)(args);
}
}
Do this instead, I think this will work and avoids an extra call (and
having to do the argument plumbing that inevitably comes with this kind
of wrapping):
template opDispatch(string name) {
alias opdispatch(T) = other_name!(name, T);
}
template other_name(string name, T) {
auto other_name(Args...)(Args args) {
// real implementation
}
}
-Steve
Re: How to dispatch a class function for an object accessed by handle?
On 3/6/20 9:42 AM, Steven Schveighoffer wrote: alias opdispatch(T) = other_name!(name, T); And obviously, this should be opDispatch with a capital D ! -Steve
Re: How to dispatch a class function for an object accessed by handle?
On Friday, 6 March 2020 at 14:05:55 UTC, Steven Schveighoffer
wrote:
Adam's way doesn't work either, because the call doesn't use
the alias, but just instantiates opDispatch with the new name!'
oh yikes, how did I not notice that?!
so yeah just kinda screwed. I'd probably suggest at tis point
having the opDispatch be a trivial implementation that just
forwards to another named method.
struct A {
template opDispatch(string name) {
auto opDispatch(T, Args...)(Args args) {
return other_name!(name, T, Args)(args);
}
}
auto other_name(string name, T, Args...)(Args args) {
// real implementation
}
}
and then to test it externally you do
a.other_name!("whatever", Bitmap)(args, here);
Re: How to dispatch a class function for an object accessed by handle?
On 3/6/20 8:55 AM, Steven Schveighoffer wrote:
Instantiate!(f.opDispatch!fname, Bitmap)("path/to/wallpaper.png")
I realized, this doesn't work. Because f.opDispatch is a `this` call,
but is not called that way in this case.
Adam's way doesn't work either, because the call doesn't use the alias,
but just instantiates opDispatch with the new name!
I think the only solution might be the mixin.
-Steve
Re: How to dispatch a class function for an object accessed by handle?
On 3/6/20 6:51 AM, wjoe wrote:
On Thursday, 5 March 2020 at 18:33:41 UTC, Adam D. Ruppe wrote:
On Thursday, 5 March 2020 at 14:24:33 UTC, wjoe wrote:
[...]
template opDispatch(string name) {
auto opDispatch(T, Args...)(Args args) {
...
}
}
[...]
NOTE: opDispatch suppresses internal compile errors, it will just say
"no such property whatever". you can explicitly instantiate with
`f.opDispatch!"whatever` to help see better errors.
Follow-up question:
Calling f.whatever!SomeResource(...); works no problem.
However I can't figure out how to call a function by explicitly
instantiating opDispatch.
Since f.opDispatch!"load"(handle, "wallpaper.png");
doesn't compile, I refreshed my memory about the shortcut syntax and the
eponymous syntax and the way I read it is that this is a template of a
template.
So I tried this: f.opDispatch!"load".opDispatch!Bitmap(handle,
"path/to/wallpaper.png");
This doesn't work, because an eponymous template does not provide access
to the internals of the template.
But this doesn't compile either and errors out with:
Error: Cannot resolve type for f.opDispatch(T, ARGS...)(ResourceHandle
handle, ARGS args)
I don't understand this error message. Which type can't be resolved?
Is there a way to look at output of what the compiler generates for
f.whatever!SomeResource(...); ?
You can use -vcg-ast, but this isn't necessarily going to be compilable
code.
D doesn't allow chained instantiation (i.e. (A!B)!C), so you need to use
either a mixin or a helper:
import std.meta;
enum fname = "load";
Instantiate!(f.opDispatch!fname, Bitmap)("path/to/wallpaper.png")
or
mixin("f." ~ fname ~ "!(Bitmap)(...);");
I'm assuming fname is given to you as a compile-time string and that's
why you'd need to run opDispatch manually.
-Steve
Re: How to dispatch a class function for an object accessed by handle?
On Friday, 6 March 2020 at 11:51:54 UTC, wjoe wrote:
I don't understand this error message. Which type can't be
resolved?
I don't know. It works if you rename the inner one but it
doesn't like eponymous templates like this. I suspect either the
spec subtly doesn't allow it or a compiler bug. I think the type
it is referring to is the `this` type.
You can work around with an alias:
// test rig
import std.stdio;
struct A {
template opDispatch(string name) {
auto opDispatch(T, Args...)(Args args) {
writeln(name, ".", T.stringof, "(", args, ")");
}
}
}
// workaround
void main() {
A a;
alias helper = a.opDispatch!("foo");
a.helper!(int)(5, "omg");
}
So the helper does one level, then the next level is done on the
next line to avoid the stupid "multiple ! not allowed". You need
to specify the `a` again to avoid `need this for...` due to how
aliases are kinda weird.
Huge hassle to use but if just doing it temporarily to debug it
can be livable.
Is there a way to look at output of what the compiler generates
for f.whatever!SomeResource(...); ?
-vcg-ast or something like to dmd but i never use it since
there's TONS of spam in a file called `yourfile.d.cg`
Re: How to dispatch a class function for an object accessed by handle?
On Thursday, 5 March 2020 at 18:33:41 UTC, Adam D. Ruppe wrote:
On Thursday, 5 March 2020 at 14:24:33 UTC, wjoe wrote:
[...]
template opDispatch(string name) {
auto opDispatch(T, Args...)(Args args) {
...
}
}
[...]
NOTE: opDispatch suppresses internal compile errors, it will
just say "no such property whatever". you can explicitly
instantiate with `f.opDispatch!"whatever` to help see better
errors.
Follow-up question:
Calling f.whatever!SomeResource(...); works no problem.
However I can't figure out how to call a function by explicitly
instantiating opDispatch.
Since f.opDispatch!"load"(handle, "wallpaper.png");
doesn't compile, I refreshed my memory about the shortcut syntax
and the eponymous syntax and the way I read it is that this is a
template of a template.
So I tried this: f.opDispatch!"load".opDispatch!Bitmap(handle,
"path/to/wallpaper.png");
But this doesn't compile either and errors out with:
Error: Cannot resolve type for f.opDispatch(T,
ARGS...)(ResourceHandle handle, ARGS args)
I don't understand this error message. Which type can't be
resolved?
Is there a way to look at output of what the compiler generates
for f.whatever!SomeResource(...); ?
Re: How to dispatch a class function for an object accessed by handle?
On Thursday, 5 March 2020 at 18:33:41 UTC, Adam D. Ruppe wrote:
On Thursday, 5 March 2020 at 14:24:33 UTC, wjoe wrote:
Implement this for free functions i would do something like
this
void dispatch(alias fn, ARGS...)(Handle handle, ARGS args)
Why do you need an `alias fn` like that?
My suggestion would be to just use the `opDispatch` magic
method that gives you a string, then `__traits(getMember, obj,
memberName)(args)` to call it.
But if you specifically need the alias param that won't work as
well. (You could still do `__traits(getMember, obj,
__traits(identifier, fn))` though, so it isn't ruled out
entirely, just not as nice. That is also more likely to break
with overloads btw)
struct Handle {
private Whatever obj;
auto opDispatch(string name, Args...)(Args args) {
return __traits(getMember, obj, name)(args);
}
}
And the usage would look like:
auto size = f.getSize(wallpaperhandle);
assuming the Handle knows how to store Whatever without being
told what it is again at the call site (e.g. if you actually
use an `interface` internally, or an encapsulated tagged union
or whatever).
If you do need to tell it what it is, a two-level function
gives that opportunity:
template opDispatch(string name) {
auto opDispatch(T, Args...)(Args args) {
auto obj = cast(T) o; // or whatever you do to convert
return __traits(getMember, obj, name)(args);
}
}
then the usage looks like
auto size = f.getSize!Bitmap(wallpaperhandle);
NOTE: opDispatch suppresses internal compile errors, it will
just say "no such property whatever". you can explicitly
instantiate with `f.opDispatch!"whatever` to help see better
errors.
But it depends on what exactly you are doing.
Thanks for your reply:)
I don't need an alias at all. I was trying to figure something
out with opDispatch first but something like __traits(getMember,
obj, name)(args); never occurred to me. Awesome!
The handle knows whether or not it's valid and where to find the
object and it only makes sense in the context of the factory that
made it.
The template opDispatch looks like what I was looking for :)
Re: How to dispatch a class function for an object accessed by handle?
On Thursday, 5 March 2020 at 14:46:24 UTC, Steven Schveighoffer
wrote:
On 3/5/20 9:24 AM, wjoe wrote:
but how can I call fn in the context of an object instance?
You could do it with delegates. But it's ugly:
import std.stdio;
class C
{
void foo() { writeln("Yup");}
}
void main()
{
alias f = C.foo;
auto c = new C;
void delegate() dg;
dg.funcptr = &f;
dg.ptr = cast(void*)c;
dg(); // prints "Yup"
}
I don't know of a way to call f with c aside from this.
-Steve
I have an ugly implementation with a one liner mixin and I don't
like it. Your solution
looks interesting but I think that's more code than my current
solution. Thanks for your reply though.
Re: How to dispatch a class function for an object accessed by handle?
On Thursday, 5 March 2020 at 14:24:33 UTC, wjoe wrote:
Implement this for free functions i would do something like this
void dispatch(alias fn, ARGS...)(Handle handle, ARGS args)
Why do you need an `alias fn` like that?
My suggestion would be to just use the `opDispatch` magic method
that gives you a string, then `__traits(getMember, obj,
memberName)(args)` to call it.
But if you specifically need the alias param that won't work as
well. (You could still do `__traits(getMember, obj,
__traits(identifier, fn))` though, so it isn't ruled out
entirely, just not as nice. That is also more likely to break
with overloads btw)
struct Handle {
private Whatever obj;
auto opDispatch(string name, Args...)(Args args) {
return __traits(getMember, obj, name)(args);
}
}
And the usage would look like:
auto size = f.getSize(wallpaperhandle);
assuming the Handle knows how to store Whatever without being
told what it is again at the call site (e.g. if you actually use
an `interface` internally, or an encapsulated tagged union or
whatever).
If you do need to tell it what it is, a two-level function gives
that opportunity:
template opDispatch(string name) {
auto opDispatch(T, Args...)(Args args) {
auto obj = cast(T) o; // or whatever you do to convert
return __traits(getMember, obj, name)(args);
}
}
then the usage looks like
auto size = f.getSize!Bitmap(wallpaperhandle);
NOTE: opDispatch suppresses internal compile errors, it will just
say "no such property whatever". you can explicitly instantiate
with `f.opDispatch!"whatever` to help see better errors.
But it depends on what exactly you are doing.
Re: How to dispatch a class function for an object accessed by handle?
On 3/5/20 9:24 AM, wjoe wrote:
but how can I call fn in the context of an object instance?
You could do it with delegates. But it's ugly:
import std.stdio;
class C
{
void foo() { writeln("Yup");}
}
void main()
{
alias f = C.foo;
auto c = new C;
void delegate() dg;
dg.funcptr = &f;
dg.ptr = cast(void*)c;
dg(); // prints "Yup"
}
I don't know of a way to call f with c aside from this.
-Steve
