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digitalmars.D.bugs - [Issue 6617] New: Two problems using enum lenghs

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=6617

           Summary: Two problems using enum lenghs
           Product: D
           Version: D2
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Keywords: rejects-valid
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: bearophile_hugs eml.cc



This is a bug report. I have found two different problems while creating a
fixed-sized array as long as the number members of an enum (DMD 2.055beta3):


import std.traits: EnumMembers;
enum Foo : size_t { A = 0, B = 1, C = 2 }
void main() {
    int[(EnumMembers!(Foo)).length] bar1; // Error: EnumMembers!(Foo) is used
as a type
    enum size_t nmembers0 = (EnumMembers!(Foo)).length; // Error:
EnumMembers!(Foo) is used as a type
    alias EnumMembers!(Foo) members;
    int[members.length] bar2; // Error: identifier 'length' of 'members.length'
is not defined
    enum size_t nmembers = members.length;
    int[nmembers] bar3; // OK
}


---------------

In practice I think a length attribute for enums is handy to have (this is a
low-priority enhacement request):


enum Foo : size_t { A = 0, B = 1, C = 2 }
void main() {
    int[Foo.length] bar;
}

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Sep 07 2011
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=6617


Tommi <tommitissari hotmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tommitissari hotmail.com





 In practice I think a length attribute for enums is handy to have (this is a
 low-priority enhacement request):


I think it's a good enhancement, but instead of "length" it should be called
"count".

Tool {hammer, drill, screwdriver}

Tool.count;  // a lot better than Tool.length

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Jul 16 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Andrej Mitrovic <andrej.mitrovich gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|rejects-valid               |
                 CC|                            |andrej.mitrovich gmail.com
           Severity|normal                      |enhancement



10:06:34 PST ---


 This is a bug report. I have found two different problems while creating a
 fixed-sized array as long as the number members of an enum (DMD 2.055beta3)


All of these now work.


 In practice I think a length attribute for enums is handy to have (this is a
 low-priority enhacement request):
 enum Foo : size_t { A = 0, B = 1, C = 2 }
 void main() {
     int[Foo.length] bar;
 }


The problem with this is that lookups also go to the base type of the enum, so:

struct T
{
     property static size_t length() { return 0; }
}

enum Foo : T { a = T() }

void main()
{
    assert(Foo.length == 1);  // fails
}

We could instead provide a template in std.traits:

template EnumLength(E) if (is(E == enum))
{
    enum size_t EnumLength = EnumMembers!E.length;
}

void main()
{
    assert(EnumLength!Foo == 1);
}

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED







 This is a bug report. I have found two different problems while creating a
 fixed-sized array as long as the number members of an enum (DMD 2.055beta3)


 
 All of these now work.


Right, I close this bug report. Issue 4997 covers the enhancement request.



 The problem with this is that lookups also go to the base type of the enum, so:
 
 struct T
 {
      property static size_t length() { return 0; }
 }
 
 enum Foo : T { a = T() }
 
 void main()
 {
     assert(Foo.length == 1);  // fails
 }


Enums already have some built-in attributes, that cause some troubles. In 
Issue 4997 I have suggested a namespace named "meta", so you write
"MyEnum.meta.length". But then a problem is that MyEnum.meta.max breaks the
convention that D integral types have a "max" attribute.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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 We could instead provide a template in std.traits:
 
 template EnumLength(E) if (is(E == enum))
 {
     enum size_t EnumLength = EnumMembers!E.length;
 }
 
 void main()
 {
     assert(EnumLength!Foo == 1);
 }


I think this gives too much little improvement :-) Such EnumLength template is
not needed in Phobos.

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Dec 02 2012
prev sibling parent d-bugmail puremagic.com writes:
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10:52:48 PST ---


 Enums already have some built-in attributes, that cause some troubles. In 
 Issue 4997 I have suggested a namespace named "meta", so you write
 "MyEnum.meta.length".


This is also implementable via a template that exposes some fields that you
need. There's no need to hack around the compiler for this.

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