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digitalmars.D.learn - Inconsistency with function pointers

reply Russel Winder <russel winder.org.uk> writes:
I am sure I am just missing something simple, but I need the nudge=E2=80=A6

I can do:

        import core.thread ;
        import std.stdio ;
       =20
        int main(immutable string[] args) {
          auto f() { return delegate () { writeln("Hello World."); }; }
          auto t =3D new Thread(f);
          t.start();
          t.join();
          return 0;
        }

it is Thread(f) rather than Thread(&f) because f is a function returning
a void delegate() rather than being a void(). However:

        import core.thread ;
        import std.stdio ;
       =20
        int main(immutable string[] args) {
          auto t =3D new Thread( delegate () { return delegate () { writeln=
("Hello World."); }; } ) ;
          t.start();
          t.join();
          return 0;
        }

trial.d(7): Error: constructor core.thread.Thread.this (void function()
fn, ulong sz =3D cast(ulong)0) is not callable using argument types (void
delegate() delegate() pure nothrow  safe)
Failed: 'dmd' '-v' '-o-' 'trial.d' '-I.'

So I cannot use an anonymous delegate where I can use a named delegate?
--=20
Russel.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
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=3D=3D
Dr Russel Winder      t: +44 20 7585 2200   voip: sip:russel.winder ekiga.n=
et
41 Buckmaster Road    m: +44 7770 465 077   xmpp: russel winder.org.uk
London SW11 1EN, UK   w: www.russel.org.uk  skype: russel_winder
Aug 04 2012
next sibling parent reply Jacob Carlborg <doob me.com> writes:
On 2012-08-04 17:06, Russel Winder wrote:

 I am sure I am just missing something simple, but I need the nudge…

 I can do:

          import core.thread ;
          import std.stdio ;

          int main(immutable string[] args) {
            auto f() { return delegate () { writeln("Hello World."); }; }
            auto t = new Thread(f);
            t.start();
            t.join();
            return 0;
          }

 it is Thread(f) rather than Thread(&f) because f is a function returning
 a void delegate() rather than being a void(). However:

          import core.thread ;
          import std.stdio ;

          int main(immutable string[] args) {
            auto t = new Thread( delegate () { return delegate () {
writeln("Hello World."); }; } ) ;
            t.start();
            t.join();
            return 0;
          }

 trial.d(7): Error: constructor core.thread.Thread.this (void function()
 fn, ulong sz = cast(ulong)0) is not callable using argument types (void
 delegate() delegate() pure nothrow  safe)
 Failed: 'dmd' '-v' '-o-' 'trial.d' '-I.'

 So I cannot use an anonymous delegate where I can use a named delegate?


If you take a look at the declaration of the constructor for "Thread" 
you can see that it expects a function pointer. I'm not sure what's 
happening in the first example. I don't think any of the above examples 
should work.

-- 
/Jacob Carlborg
Aug 04 2012
parent reply Russel Winder <russel winder.org.uk> writes:
Jacob,

On Sat, 2012-08-04 at 18:02 +0200, Jacob Carlborg wrote:

 On 2012-08-04 17:06, Russel Winder wrote:

 I am sure I am just missing something simple, but I need the nudge=E2=




=80=A6

 I can do:

          import core.thread ;
          import std.stdio ;

          int main(immutable string[] args) {
            auto f() { return delegate () { writeln("Hello World."); }; =




}

Changing this to function makes no difference to the fact that this
works.


            auto t =3D new Thread(f);




Put &f here and the compiler says:

threadFunctionPointerTrial.d(6): Error: constructor core.thread.Thread.this=
 (void function() fn, ulong sz =3D cast(ulong)0) is not callable using argu=
ment types (void function() delegate())
threadFunctionPointerTrial.d(6): Error: cannot implicitly convert expressio=
n (&f) of type void function() delegate() to void delegate()
Failed: 'dmd' '-v' '-o-' 'threadFunctionPointerTrial.d' '-I.'


            t.start();
            t.join();
            return 0;
          }

 it is Thread(f) rather than Thread(&f) because f is a function returnin=




g

 a void delegate() rather than being a void(). However:

          import core.thread ;
          import std.stdio ;

          int main(immutable string[] args) {
            auto t =3D new Thread( delegate () { return delegate () { wr=




iteln("Hello World."); }; } ) ;

            t.start();
            t.join();
            return 0;
          }

 trial.d(7): Error: constructor core.thread.Thread.this (void function()
 fn, ulong sz =3D cast(ulong)0) is not callable using argument types (vo=




id

 delegate() delegate() pure nothrow  safe)
 Failed: 'dmd' '-v' '-o-' 'trial.d' '-I.'

 So I cannot use an anonymous delegate where I can use a named delegate?


=20
 If you take a look at the declaration of the constructor for "Thread"=20
 you can see that it expects a function pointer. I'm not sure what's=20
 happening in the first example. I don't think any of the above examples=


=20

 should work.


Isn't there an overload for function and one for delegate?

threadFunctionPointerUnnamed.d(5): Error: constructor core.thread.Thread.th=
is called with argument types:
	((void function()))
matches both:
	core.thread.Thread.this(void function() fn, ulong sz =3D cast(ulong)0)
and:
	core.thread.Thread.this(void delegate() dg, ulong sz =3D cast(ulong)0)
Failed: 'dmd' '-v' '-o-' 'threadFunctionPointerUnnamed.d' '-I.'

--=20
Russel.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
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=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D
Dr Russel Winder      t: +44 20 7585 2200   voip: sip:russel.winder ekiga.n=
et
41 Buckmaster Road    m: +44 7770 465 077   xmpp: russel winder.org.uk
London SW11 1EN, UK   w: www.russel.org.uk  skype: russel_winder
Aug 04 2012
parent Jacob Carlborg <doob me.com> writes:
On 2012-08-04 18:41, Russel Winder wrote:


 Isn't there an overload for function and one for delegate?

 threadFunctionPointerUnnamed.d(5): Error: constructor core.thread.Thread.this
called with argument types:
 	((void function()))
 matches both:
 	core.thread.Thread.this(void function() fn, ulong sz = cast(ulong)0)
 and:
 	core.thread.Thread.this(void delegate() dg, ulong sz = cast(ulong)0)
 Failed: 'dmd' '-v' '-o-' 'threadFunctionPointerUnnamed.d' '-I.'


Hmm, right. I didn't scroll down far enough. Then I don't know.

-- 
/Jacob Carlborg
Aug 04 2012
prev sibling next sibling parent "anonymous" <anonymous example.com> writes:
On Saturday, 4 August 2012 at 15:23:39 UTC, Russel Winder wrote:
[...]

 I can do:


[...]

           auto f() { return delegate () { writeln("Hello 
 World."); }; }
           auto t = new Thread(f);


[...]

 However:


[...]

           auto t = new Thread( delegate () { return delegate () 
 { writeln("Hello World."); }; } ) ;


[doesn't work]

You need parentheses to call the anonymous delegate:
auto t = new Thread( delegate () { return delegate () {
writeln("Hello World."); }; }()) ;

You don't need them with f, because there you have to write &f to
refer to the delegate itself. (And because you don't use
-property.)
Aug 04 2012
prev sibling parent reply "David Nadlinger" <see klickverbot.at> writes:
On Saturday, 4 August 2012 at 15:23:39 UTC, Russel Winder wrote:

 trial.d(7): Error: constructor core.thread.Thread.this (void 
 function()
 fn, ulong sz = cast(ulong)0) is not callable using argument 
 types (void
 delegate() delegate() pure nothrow  safe)
 Failed: 'dmd' '-v' '-o-' 'trial.d' '-I.'

 So I cannot use an anonymous delegate where I can use a named 
 delegate?


You are trying to pass a delegate which returns a delegate – 
this isn't going to work. ;)

In your first example is that f is implicitly called due to the 
non-strict property syntax.

David
Aug 04 2012
next sibling parent "David Nadlinger" <see klickverbot.at> writes:
On Saturday, 4 August 2012 at 19:03:30 UTC, David Nadlinger wrote:

 In your first example is that […]


Darn, make this »In your first example, …«.
Aug 04 2012
prev sibling parent Russel Winder <russel winder.org.uk> writes:
On Sat, 2012-08-04 at 21:03 +0200, David Nadlinger wrote:
[=E2=80=A6]

 You are trying to pass a delegate which returns a delegate =E2=80=93=20
 this isn't going to work. ;)


But that is my whole point, it does a lot of the time, and it depends on
whether you are working with named functions and delegates or with
anonymous functions and delegates.


 In your first example is that f is implicitly called due to the=20
 non-strict property syntax.


OK, so this is looking like the nudge that anonymous was also talking
about, but from a different viewpoint. It seems there is implicit
behaviour going on here that is creating right royal confusion on the
part of at least one programmer, me.

The parameter I think I am passing to thread construction is sometimes,
but not mostly, not the parameter the Thread constructors are receiving.
This looks like it is going to violate the Principle of Least
Surprise :-(

--=20
Russel.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
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=3D=3D
Dr Russel Winder      t: +44 20 7585 2200   voip: sip:russel.winder ekiga.n=
et
41 Buckmaster Road    m: +44 7770 465 077   xmpp: russel winder.org.uk
London SW11 1EN, UK   w: www.russel.org.uk  skype: russel_winder
Aug 04 2012