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digitalmars.D.learn - function pointer as the enum base type

reply mumba <qniol o2.pl> writes:
Idea: to make an enum type with function pointers as it's elements.
Problem: no more than one element can be inserted!

$echo '
void foo() {}
void bar() {}

enum Enum : void function() {
    FOO = &foo,
    BAR = &bar
}

int main() { return 0;	}' > enum.d
$dmd --help
Digital Mars D Compiler v2.014
Copyright (c) 1999-2008 by Digital Mars written by Walter Bright
Documentation: http://www.digitalmars.com/d/2.0/index.html
...
$dmd enum.d
enum.d(5): Error: Integer constant expression expected instead of (& bar) < (&
foo)
enum.d(5): Error: Integer constant expression expected instead of (& bar) > (&
foo)


I don't understand the error message. 
First - why integer constant expression expected, if it's supposed to be the
function based enum? Second - instead of what? (& bar) expression, which is
smaller than (& foo), or boolean expression (& bar) < (& foo)? 
Third - in both cases: if only one of these messages appeard - it would be just
strange for me. But as they are together and both refer to the same line - I'm
knocked out. What logic leads to such mutually exclusive pieces of information?

Please someone explain it to me.

By the way:

enum Enum : void function() {
    FOO = &foo
}

works fine.


cheers
Oct 05 2008
next sibling parent mumba <qniol o2.pl> writes:
mumba Wrote:

uh, sorry :( . The error message refers to the 7th line. To this, to be precise:

BAR = &bar
Oct 05 2008
prev sibling next sibling parent reply "Denis Koroskin" <2korden gmail.com> writes:
On Mon, 06 Oct 2008 03:21:09 +0400, mumba <qniol o2.pl> wrote:


 Idea: to make an enum type with function pointers as it's elements.
 Problem: no more than one element can be inserted!

 $echo '
 void foo() {}
 void bar() {}

 enum Enum : void function() {
     FOO = &foo,
     BAR = &bar
 }

 int main() { return 0;	}' > enum.d
 $dmd --help
 Digital Mars D Compiler v2.014
 Copyright (c) 1999-2008 by Digital Mars written by Walter Bright
 Documentation: http://www.digitalmars.com/d/2.0/index.html
 ...
 $dmd enum.d
 enum.d(5): Error: Integer constant expression expected instead of (&  
 bar) < (& foo)
 enum.d(5): Error: Integer constant expression expected instead of (&  
 bar) > (& foo)


 I don't understand the error message.
 First - why integer constant expression expected, if it's supposed to be  
 the function based enum? Second - instead of what? (& bar) expression,  
 which is smaller than (& foo), or boolean expression (& bar) < (& foo)?
 Third - in both cases: if only one of these messages appeard - it would  
 be just strange for me. But as they are together and both refer to the  
 same line - I'm knocked out. What logic leads to such mutually exclusive  
 pieces of information?

 Please someone explain it to me.

 By the way:

 enum Enum : void function() {
     FOO = &foo
 }

 works fine.


 cheers



Looks like it can't sort the enum values at compile time. That's because  
&foo and &bar are not known until codegen phase.
Oct 05 2008
next sibling parent reply "Jarrett Billingsley" <jarrett.billingsley gmail.com> writes:
On Sun, Oct 5, 2008 at 7:26 PM, Denis Koroskin <2korden gmail.com> wrote:

 On Mon, 06 Oct 2008 03:21:09 +0400, mumba <qniol o2.pl> wrote:


 Idea: to make an enum type with function pointers as it's elements.
 Problem: no more than one element can be inserted!

 $echo '
 void foo() {}
 void bar() {}

 enum Enum : void function() {
    FOO = &foo,
    BAR = &bar
 }

 int main() { return 0;  }' > enum.d
 $dmd --help
 Digital Mars D Compiler v2.014
 Copyright (c) 1999-2008 by Digital Mars written by Walter Bright
 Documentation: http://www.digitalmars.com/d/2.0/index.html
 ...
 $dmd enum.d
 enum.d(5): Error: Integer constant expression expected instead of (& bar)
 < (& foo)
 enum.d(5): Error: Integer constant expression expected instead of (& bar)

 (& foo)



 I don't understand the error message.
 First - why integer constant expression expected, if it's supposed to be
 the function based enum? Second - instead of what? (& bar) expression, which
 is smaller than (& foo), or boolean expression (& bar) < (& foo)?
 Third - in both cases: if only one of these messages appeard - it would be
 just strange for me. But as they are together and both refer to the same
 line - I'm knocked out. What logic leads to such mutually exclusive pieces
 of information?

 Please someone explain it to me.

 By the way:

 enum Enum : void function() {
    FOO = &foo
 }

 works fine.


 cheers



 Looks like it can't sort the enum values at compile time. That's because
 &foo and &bar are not known until codegen phase.


Nothing of the sort.  Enums must derive from an integer or boolean
type, which function pointers certainly are not.  It's perfectly fine
to say:

const FOO = &foo;
Oct 05 2008
next sibling parent reply "Denis Koroskin" <2korden gmail.com> writes:
On Mon, 06 Oct 2008 03:33:05 +0400, Jarrett Billingsley  
<jarrett.billingsley gmail.com> wrote:


 On Sun, Oct 5, 2008 at 7:26 PM, Denis Koroskin <2korden gmail.com> wrote:

 On Mon, 06 Oct 2008 03:21:09 +0400, mumba <qniol o2.pl> wrote:


 Idea: to make an enum type with function pointers as it's elements.
 Problem: no more than one element can be inserted!

 $echo '
 void foo() {}
 void bar() {}

 enum Enum : void function() {
    FOO = &foo,
    BAR = &bar
 }

 int main() { return 0;  }' > enum.d
 $dmd --help
 Digital Mars D Compiler v2.014
 Copyright (c) 1999-2008 by Digital Mars written by Walter Bright
 Documentation: http://www.digitalmars.com/d/2.0/index.html
 ...
 $dmd enum.d
 enum.d(5): Error: Integer constant expression expected instead of (&  
 bar)
 < (& foo)
 enum.d(5): Error: Integer constant expression expected instead of (&  
 bar)

 (& foo)



 I don't understand the error message.
 First - why integer constant expression expected, if it's supposed to  
 be
 the function based enum? Second - instead of what? (& bar) expression,  
 which
 is smaller than (& foo), or boolean expression (& bar) < (& foo)?
 Third - in both cases: if only one of these messages appeard - it  
 would be
 just strange for me. But as they are together and both refer to the  
 same
 line - I'm knocked out. What logic leads to such mutually exclusive  
 pieces
 of information?

 Please someone explain it to me.

 By the way:

 enum Enum : void function() {
    FOO = &foo
 }

 works fine.


 cheers



 Looks like it can't sort the enum values at compile time. That's because
 &foo and &bar are not known until codegen phase.


 Nothing of the sort.  Enums must derive from an integer or boolean
 type, which function pointers certainly are not.  It's perfectly fine
 to say:

 const FOO = &foo;


Yeah, of course. But why the following works?

import std.stdio;

int foo() { return 42; }

enum Enum : int function() {
     FOO = &foo,
//  BAR = &foo    // uncomment the line and it stops working
}

int main()
{
	writefln(Enum.FOO());
	return 0;
}
Oct 05 2008
parent Robert Fraser <fraserofthenight gmail.com> writes:
Denis Koroskin wrote:

 On Mon, 06 Oct 2008 03:33:05 +0400, Jarrett Billingsley 
 <jarrett.billingsley gmail.com> wrote:
 

 On Sun, Oct 5, 2008 at 7:26 PM, Denis Koroskin <2korden gmail.com> wrote:

 On Mon, 06 Oct 2008 03:21:09 +0400, mumba <qniol o2.pl> wrote:


 Idea: to make an enum type with function pointers as it's elements.
 Problem: no more than one element can be inserted!

 $echo '
 void foo() {}
 void bar() {}

 enum Enum : void function() {
    FOO = &foo,
    BAR = &bar
 }

 int main() { return 0;  }' > enum.d
 $dmd --help
 Digital Mars D Compiler v2.014
 Copyright (c) 1999-2008 by Digital Mars written by Walter Bright
 Documentation: http://www.digitalmars.com/d/2.0/index.html
 ...
 $dmd enum.d
 enum.d(5): Error: Integer constant expression expected instead of (& 
 bar)
 < (& foo)
 enum.d(5): Error: Integer constant expression expected instead of (& 
 bar)

 (& foo)



 I don't understand the error message.
 First - why integer constant expression expected, if it's supposed 
 to be
 the function based enum? Second - instead of what? (& bar) 
 expression, which
 is smaller than (& foo), or boolean expression (& bar) < (& foo)?
 Third - in both cases: if only one of these messages appeard - it 
 would be
 just strange for me. But as they are together and both refer to the 
 same
 line - I'm knocked out. What logic leads to such mutually exclusive 
 pieces
 of information?

 Please someone explain it to me.

 By the way:

 enum Enum : void function() {
    FOO = &foo
 }

 works fine.


 cheers



 Looks like it can't sort the enum values at compile time. That's because
 &foo and &bar are not known until codegen phase.


 Nothing of the sort.  Enums must derive from an integer or boolean
 type, which function pointers certainly are not.  It's perfectly fine
 to say:

 const FOO = &foo;


 
 Yeah, of course. But why the following works?
 
 import std.stdio;
 
 int foo() { return 42; }
 
 enum Enum : int function() {
     FOO = &foo,
 //  BAR = &foo    // uncomment the line and it stops working
 }
 
 int main()
 {
     writefln(Enum.FOO());
     return 0;
 }


I would call that a "bug".
Oct 05 2008
prev sibling parent "Steven Schveighoffer" <schveiguy yahoo.com> writes:
"Jarrett Billingsley" wrote

 On Sun, Oct 5, 2008 at 7:26 PM, Denis Koroskin <2korden gmail.com> wrote:

 On Mon, 06 Oct 2008 03:21:09 +0400, mumba <qniol o2.pl> wrote:


 Idea: to make an enum type with function pointers as it's elements.
 Problem: no more than one element can be inserted!

 $echo '
 void foo() {}
 void bar() {}

 enum Enum : void function() {
    FOO = &foo,
    BAR = &bar
 }

 int main() { return 0;  }' > enum.d
 $dmd --help
 Digital Mars D Compiler v2.014
 Copyright (c) 1999-2008 by Digital Mars written by Walter Bright
 Documentation: http://www.digitalmars.com/d/2.0/index.html
 ...
 $dmd enum.d
 enum.d(5): Error: Integer constant expression expected instead of (& 
 bar)
 < (& foo)
 enum.d(5): Error: Integer constant expression expected instead of (& 
 bar)

 (& foo)



 I don't understand the error message.
 First - why integer constant expression expected, if it's supposed to be
 the function based enum? Second - instead of what? (& bar) expression, 
 which
 is smaller than (& foo), or boolean expression (& bar) < (& foo)?
 Third - in both cases: if only one of these messages appeard - it would 
 be
 just strange for me. But as they are together and both refer to the same
 line - I'm knocked out. What logic leads to such mutually exclusive 
 pieces
 of information?

 Please someone explain it to me.

 By the way:

 enum Enum : void function() {
    FOO = &foo
 }

 works fine.


 cheers



 Looks like it can't sort the enum values at compile time. That's because
 &foo and &bar are not known until codegen phase.


 Nothing of the sort.  Enums must derive from an integer or boolean
 type, which function pointers certainly are not.  It's perfectly fine
 to say:

 const FOO = &foo;


AFAIK, enums can derive from any type in D2, including non-integer types.  I 
think the request is reasonable for D2, where enum wears many hats.

-Steve
Oct 06 2008
prev sibling parent mumba <qniol o2.pl> writes:
Denis Koroskin Wrote:


 Looks like it can't sort the enum values at compile time. That's because  
 &foo and &bar are not known until codegen phase.


That's another thing I'm meditating on. Why do we need any kind of ordering in
enum types? Isn't it supposed to be the SET of possible values? Set containing
not necessarily orderable elements?
Oct 05 2008
prev sibling parent BCS <ao pathlink.com> writes:
Reply to mumba,


 Idea: to make an enum type with function pointers as it's elements.


If some way was included to enforce the values being in the set.. Vote++;
Oct 05 2008