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digitalmars.D.learn - Emulating enums

reply "JS" <js.mdnq gmail.com> writes:
http://dpaste.dzfl.pl/dbb40dbc

The code was pared down from a lot of string mixin code 
generation. I nest the structs because I want a nested enums. I 
don't want have to have eState and eStateType but eState and 
eState.Type.

Having the ability to nest enums would solve my problem.

Regardless, I can almost achieve the effect with nested structs 
but not quite.

In the code, I cannot assign to the struct for some reason even 
with alias this on iB, which should make State act like the int 
Value.

i.e.,

b.State.Value = Enums.State.A;

works but

b.State = Enums.State.A;

doesn't

It maybe some stupid error on my part but I can't keep my eyes 
open enough to figure it out...
Jul 31 2013
parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 07/31/2013 06:10 PM, JS wrote:

 http://dpaste.dzfl.pl/dbb40dbc

 The code was pared down from a lot of string mixin code generation. I
 nest the structs because I want a nested enums. I don't want have to
 have eState and eStateType but eState and eState.Type.

 Having the ability to nest enums would solve my problem.

 Regardless, I can almost achieve the effect with nested structs but not
 quite.

 In the code, I cannot assign to the struct for some reason even with
 alias this on iB, which should make State act like the int Value.

 i.e.,

 b.State.Value = Enums.State.A;

 works but

 b.State = Enums.State.A;

 doesn't

 It maybe some stupid error on my part but I can't keep my eyes open
 enough to figure it out...


For that assignment to work, the left-hand side must be assignable. 
However, the property function State() returns Enums.eState by-value.

The following has the same issue:

struct S
{
     int i_;

      property int i() {
         return i_;
     }

     alias i this;
}

void main()
{
     auto s = S();
     s = 42;
     assert(s.i == 42);
}

Error: cannot implicitly convert expression (42) of type int to S

To compile, i() must return an lvalue:

      property ref int i() {

Ali
Jul 31 2013
parent reply "JS" <js.mdnq gmail.com> writes:
On Thursday, 1 August 2013 at 05:22:46 UTC, Ali Çehreli wrote:

 On 07/31/2013 06:10 PM, JS wrote:

 http://dpaste.dzfl.pl/dbb40dbc

 The code was pared down from a lot of string mixin code 
 generation. I
 nest the structs because I want a nested enums. I don't want 
 have to
 have eState and eStateType but eState and eState.Type.

 Having the ability to nest enums would solve my problem.

 Regardless, I can almost achieve the effect with nested 
 structs but not
 quite.

 In the code, I cannot assign to the struct for some reason 
 even with
 alias this on iB, which should make State act like the int 
 Value.

 i.e.,

 b.State.Value = Enums.State.A;

 works but

 b.State = Enums.State.A;

 doesn't

 It maybe some stupid error on my part but I can't keep my eyes 
 open
 enough to figure it out...


 For that assignment to work, the left-hand side must be 
 assignable. However, the property function State() returns 
 Enums.eState by-value.

 The following has the same issue:

 struct S
 {
     int i_;

      property int i() {
         return i_;
     }

     alias i this;
 }

 void main()
 {
     auto s = S();
     s = 42;
     assert(s.i == 42);
 }

 Error: cannot implicitly convert expression (42) of type int to 
 S

 To compile, i() must return an lvalue:

      property ref int i() {

 Ali


Thanks...
Aug 01 2013
parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 08/01/2013 03:29 AM, JS wrote:


 On Thursday, 1 August 2013 at 05:22:46 UTC, Ali Çehreli wrote:

 On 07/31/2013 06:10 PM, JS wrote:

 http://dpaste.dzfl.pl/dbb40dbc

 The code was pared down from a lot of string mixin code generation. I
 nest the structs because I want a nested enums. I don't want have to
 have eState and eStateType but eState and eState.Type.

 Having the ability to nest enums would solve my problem.

 Regardless, I can almost achieve the effect with nested structs but not
 quite.

 In the code, I cannot assign to the struct for some reason even with
 alias this on iB, which should make State act like the int Value.

 i.e.,

 b.State.Value = Enums.State.A;

 works but

 b.State = Enums.State.A;

 doesn't

 It maybe some stupid error on my part but I can't keep my eyes open
 enough to figure it out...


 For that assignment to work, the left-hand side must be assignable.
 However, the property function State() returns Enums.eState by-value.

 The following has the same issue:

 struct S
 {
     int i_;

      property int i() {
         return i_;
     }

     alias i this;
 }

 void main()
 {
     auto s = S();
     s = 42;
     assert(s.i == 42);
 }

 Error: cannot implicitly convert expression (42) of type int to S

 To compile, i() must return an lvalue:

      property ref int i() {




Although, what I said seems more like a workaround because you already 
had a setter  property. You shouldn't need to make the getter return a 
reference as well... I guess...

I think what is at play here is the current implementation limitation of 
"a single 'alias this' per type." I think 'alias this' happens to pick 
the getter perhaps because the getter function is defined first in the 
class. I don't know...

Ali
Aug 01 2013
next sibling parent "JS" <js.mdnq gmail.com> writes:
On Thursday, 1 August 2013 at 16:36:34 UTC, Ali Çehreli wrote:

 On 08/01/2013 03:29 AM, JS wrote:


 On Thursday, 1 August 2013 at 05:22:46 UTC, Ali Çehreli wrote:

 On 07/31/2013 06:10 PM, JS wrote:

 http://dpaste.dzfl.pl/dbb40dbc

 The code was pared down from a lot of string mixin code






 generation. I

 nest the structs because I want a nested enums. I don't






 want have to

 have eState and eStateType but eState and eState.Type.

 Having the ability to nest enums would solve my problem.

 Regardless, I can almost achieve the effect with nested






 structs but not

 quite.

 In the code, I cannot assign to the struct for some reason






 even with

 alias this on iB, which should make State act like the int






 Value.

 i.e.,

 b.State.Value = Enums.State.A;

 works but

 b.State = Enums.State.A;

 doesn't

 It maybe some stupid error on my part but I can't keep my






 eyes open

 enough to figure it out...


 For that assignment to work, the left-hand side must be




 assignable.

 However, the property function State() returns Enums.eState




 by-value.

 The following has the same issue:

 struct S
 {
     int i_;

      property int i() {
         return i_;
     }

     alias i this;
 }

 void main()
 {
     auto s = S();
     s = 42;
     assert(s.i == 42);
 }

 Error: cannot implicitly convert expression (42) of type int




 to S

 To compile, i() must return an lvalue:

      property ref int i() {




 Although, what I said seems more like a workaround because you 
 already had a setter  property. You shouldn't need to make the 
 getter return a reference as well... I guess...

 I think what is at play here is the current implementation 
 limitation of "a single 'alias this' per type." I think 'alias 
 this' happens to pick the getter perhaps because the getter 
 function is defined first in the class. I don't know...

 Ali



Yeah, I think I remember that being an issue before which kinda 
sucks as one doesn't want to have to necessarily return 
references.

alias this should also alias all the overloads.

In any case, how long has the multiple alias issue been going on? 
10 years?
Aug 01 2013
prev sibling parent "JS" <js.mdnq gmail.com> writes:
On Thursday, 1 August 2013 at 16:36:34 UTC, Ali Çehreli wrote:

 On 08/01/2013 03:29 AM, JS wrote:


 On Thursday, 1 August 2013 at 05:22:46 UTC, Ali Çehreli wrote:

 On 07/31/2013 06:10 PM, JS wrote:

 http://dpaste.dzfl.pl/dbb40dbc

 The code was pared down from a lot of string mixin code






 generation. I

 nest the structs because I want a nested enums. I don't






 want have to

 have eState and eStateType but eState and eState.Type.

 Having the ability to nest enums would solve my problem.

 Regardless, I can almost achieve the effect with nested






 structs but not

 quite.

 In the code, I cannot assign to the struct for some reason






 even with

 alias this on iB, which should make State act like the int






 Value.

 i.e.,

 b.State.Value = Enums.State.A;

 works but

 b.State = Enums.State.A;

 doesn't

 It maybe some stupid error on my part but I can't keep my






 eyes open

 enough to figure it out...


 For that assignment to work, the left-hand side must be




 assignable.

 However, the property function State() returns Enums.eState




 by-value.

 The following has the same issue:

 struct S
 {
     int i_;

      property int i() {
         return i_;
     }

     alias i this;
 }

 void main()
 {
     auto s = S();
     s = 42;
     assert(s.i == 42);
 }

 Error: cannot implicitly convert expression (42) of type int




 to S

 To compile, i() must return an lvalue:

      property ref int i() {




 Although, what I said seems more like a workaround because you 
 already had a setter  property. You shouldn't need to make the 
 getter return a reference as well... I guess...

 I think what is at play here is the current implementation 
 limitation of "a single 'alias this' per type." I think 'alias 
 this' happens to pick the getter perhaps because the getter 
 function is defined first in the class. I don't know...

 Ali


So, a ref'ed getter is the same as a setter?

Also, it would see, I'm guessing, that using alias this on a 
property and having to ref will bypass the setter?
Aug 01 2013