Re: Passing myself, a struct, as a C callback context
On Monday, 30 March 2015 at 02:53:36 UTC, Paul O'Neil wrote:
I'm registering a callback with some C code. The simplified
story is
here, but the actual code is on GitHub [1] at the end if you
care.
The call looks something like this.
void register(void(*fp)(void*), void* context);
I have a class that holds state for the callback and registers
itself:
final class Klass
{
void method()
{
register(callback_function, this);
}
}
`this` is already a reference. You're taking the address of that
reference. A simple cast should work: `cast(void*) this`.
Re: Passing myself, a struct, as a C callback context
On 3/30/15 5:12 AM, Marc =?UTF-8?B?U2Now7x0eiI=?= schue...@gmx.net
wrote:
On Monday, 30 March 2015 at 02:53:36 UTC, Paul O'Neil wrote:
I'm registering a callback with some C code. The simplified story is
here, but the actual code is on GitHub [1] at the end if you care.
The call looks something like this.
void register(void(*fp)(void*), void* context);
I have a class that holds state for the callback and registers itself:
final class Klass
{
void method()
{
register(callback_function, this);
}
}
`this` is already a reference. You're taking the address of that
reference. A simple cast should work: `cast(void*) this`.
To build on this further, this for a class is actually taking a local
stack reference, this is why it's not allowed.
And technically, cast(void*) this is dangerous in the general case
because opCast can be overridden. If you absolutely need to get a
pointer to a class reference, you would need to do this:
auto x = this;
auto p = x;
For example, for a foolproof implementation of converting a class
reference to void *, you would need to do:
auto x = this;
auto p = *(cast(void **)x);
I wonder if those who made this change thought of this problem?
-Steve
Re: Passing myself, a struct, as a C callback context
On 03/30/2015 11:32 AM, Steven Schveighoffer wrote: On 3/30/15 5:12 AM, Marc =?UTF-8?B?U2Now7x0eiI=?= schue...@gmx.net wrote: `this` is already a reference. You're taking the address of that reference. A simple cast should work: `cast(void*) this`. To build on this further, this for a class is actually taking a local stack reference, this is why it's not allowed. And technically, cast(void*) this is dangerous in the general case because opCast can be overridden. If you absolutely need to get a pointer to a class reference, you would need to do this: auto x = this; auto p = x; For example, for a foolproof implementation of converting a class reference to void *, you would need to do: auto x = this; auto p = *(cast(void **)x); I wonder if those who made this change thought of this problem? -Steve Thanks for the explanation. This makes a lot of sense - I forgot that ref actually means special pointer. Luckily, I don't plan on overriding opCast! -- Paul O'Neil Github / IRC: todayman
Passing myself, a struct, as a C callback context
I'm registering a callback with some C code. The simplified story is
here, but the actual code is on GitHub [1] at the end if you care.
The call looks something like this.
void register(void(*fp)(void*), void* context);
I have a class that holds state for the callback and registers itself:
final class Klass
{
void method()
{
register(callback_function, this);
}
}
As of dmd 2.067, doing this is deprecated. Is there an idiomatic way
to do this?
[0] Actual code is at
https://github.com/todayman/dubik/blob/master/source/vibe/core/drivers/rx.d#L177
. The msg object eventually gets passed to the registration function.
Thanks,
--
Paul O'Neil
Github / IRC: todayman
Re: Passing myself, a struct, as a C callback context
On Monday, 30 March 2015 at 02:53:36 UTC, Paul O'Neil wrote: As of dmd 2.067, doing this is deprecated. where is this documented? I don't see it in the release notes.
Re: Passing myself, a struct, as a C callback context
On 03/29/2015 10:57 PM, weaselcat wrote: On Monday, 30 March 2015 at 02:53:36 UTC, Paul O'Neil wrote: As of dmd 2.067, doing this is deprecated. where is this documented? I don't see it in the release notes. I don't see it in the release notes either, but it's happening. Maybe it's an instance of a more general thing? -- Paul O'Neil Github / IRC: todayman
Re: Passing myself, a struct, as a C callback context
On Sun, 29 Mar 2015 22:53:35 -0400, Paul O'Neil wrote:
I'm registering a callback with some C code. The simplified story is
here, but the actual code is on GitHub [1] at the end if you care.
The call looks something like this.
void register(void(*fp)(void*), void* context);
I have a class that holds state for the callback and registers itself:
final class Klass {
void method()
{
register(callback_function, this);
}
}
As of dmd 2.067, doing this is deprecated. Is there an idiomatic way
to do this?
[0] Actual code is at
https://github.com/todayman/dubik/blob/master/source/vibe/core/drivers/
rx.d#L177
. The msg object eventually gets passed to the registration function.
Thanks,
you still can cast `this` to void pointer: `cast(void*)this`
but beware of possible `opCast` overloads for `void*` (there are no in
stdlib, but...)
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Description: PGP signature
Re: Passing myself, a struct, as a C callback context
On Monday, 30 March 2015 at 02:53:36 UTC, Paul O'Neil wrote:
I'm registering a callback with some C code. The simplified
story is
here, but the actual code is on GitHub [1] at the end if you
care.
The call looks something like this.
void register(void(*fp)(void*), void* context);
I have a class that holds state for the callback and registers
itself:
final class Klass
{
void method()
{
register(callback_function, this);
}
}
As of dmd 2.067, doing this is deprecated. Is there an
idiomatic way
to do this?
[0] Actual code is at
https://github.com/todayman/dubik/blob/master/source/vibe/core/drivers/rx.d#L177
. The msg object eventually gets passed to the registration
function.
Thanks,
This is only deprecated for class not struct. This code below
works fine:
---
import std.stdio;
extern(C) void f2(void* ins) {
auto s = cast(S*)(ins);
writefln(f2():%s, s);
writefln(f2():%s, *s);
}
void f1(void* ins) {
auto s = cast(S*)(ins);
writefln(f1():%s, s);
writefln(f1():%s, *s);
}
struct S { // -- change to class to get deprecated message
int value = 10;
void f() {
f1(this);
f2(this);
}
}
void main()
{
auto s = S();
s.f();
}
---
bye,
lobo
Re: Passing myself, a struct, as a C callback context
On Monday, 30 March 2015 at 03:02:07 UTC, Paul O'Neil wrote: On 03/29/2015 10:57 PM, weaselcat wrote: On Monday, 30 March 2015 at 02:53:36 UTC, Paul O'Neil wrote: As of dmd 2.067, doing this is deprecated. where is this documented? I don't see it in the release notes. I don't see it in the release notes either, but it's happening. Maybe it's an instance of a more general thing? if it works in 2.066 you should submit a bug report, either this shouldn't be a deprecation or it should be in the release notes.
