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digitalmars.D.learn - Can Enums be integral types?

reply Manfred Nowak <svv1999 hotmail.com> writes:
In the specs(17) about enums the word "integral" has no match. 
But because the default basetype is `int`, which is an integral 
type, enums might be integral types whenever their basetype is an 
integral type.

On the other hand the specs(7.6.5.3) about types say
| A bool value can be implicitly converted to any integral type,
| with false becoming 0 and true becoming 1.

This seems senseless, when the enum has no names defined for one 
of these values.
Apr 16 2022
parent reply Bastiaan Veelo <Bastiaan Veelo.net> writes:
On Saturday, 16 April 2022 at 11:39:01 UTC, Manfred Nowak wrote:

 In the specs(17) about enums the word "integral" has no match. 
 But because the default basetype is `int`, which is an integral 
 type, enums might be integral types whenever their basetype is 
 an integral type.

 On the other hand the specs(7.6.5.3) about types say
 | A bool value can be implicitly converted to any integral type,
 | with false becoming 0 and true becoming 1.

 This seems senseless, when the enum has no names defined for 
 one of these values.


Not sure where the question is, but 
[6.5.3](https://dlang.org/spec/type.html#bool) makes that this 
works:
```d
int i = true; // 1
```
However this does not:
```d
enum E : int {Zero, One, Two}
E e1 = true; // Error: cannot implicitly convert expression 
`true` of type `bool` to `E`
E e2 = 1; // Error: cannot implicitly convert expression `1` of 
type `int` to `E`
```
The reason is in [17.1.5](https://dlang.org/spec/enum.html): 
“EnumBaseType types cannot be implicitly cast to an enum type.”

— Bastiaan.
Apr 17 2022
next sibling parent reply Era Scarecrow <rtcvb32 yahoo.com> writes:
On Sunday, 17 April 2022 at 18:25:32 UTC, Bastiaan Veelo wrote:

 On Saturday, 16 April 2022 at 11:39:01 UTC, Manfred Nowak wrote:

 In the specs(17) about enums the word "integral" has no match. 
 But because the default basetype is `int`, which is an 
 integral type, enums might be integral types whenever their 
 basetype is an integral type.


 The reason is in [17.1.5](https://dlang.org/spec/enum.html):  
 “EnumBaseType types cannot be implicitly cast to an enum type.”


The 'integral' or numeric value is used for uniqueness, not for 
math or some other effect, anymore than a primary int key in a 
SQL database is used to identify someone's birthday. (*Maybe 
that's the wrong analogy, comparing apples to oranges perhaps*).

  We will indeed have to explicitly cast to get around it, though 
it doesn't mean much. If you have say true=1, blue=2, what is 
blue+true? Numerically it's 3 but there's no value 3, or value 3 
could be say potato...

  Few years ago i made an enum type flag/library storage library, 
which would take an int and convert to N flags, or N flags to an 
int for compactly storing said values. But it's been quite a 
while, though i do recall a lot of casting and binary 
AND/OR/XOR's involved for it to work the way it was intended.
Apr 18 2022
parent reply Bastiaan Veelo <Bastiaan Veelo.net> writes:
On Tuesday, 19 April 2022 at 01:25:13 UTC, Era Scarecrow wrote:

 The 'integral' or numeric value is used for uniqueness, […]


There is nothing that requires enum values to be unique, though:
```d
import std;
void main()
{
     enum E {Zero = 0, One = 0, Two = 0}
     writeln(E.Two); // Zero!
}
```

— Bastiaan.
Apr 19 2022
parent Era Scarecrow <rtcvb32 yahoo.com> writes:
On Tuesday, 19 April 2022 at 13:20:21 UTC, Bastiaan Veelo wrote:

 There is nothing that requires enum values to be unique, though:
 ```d
 import std;
 void main()
 {
     enum E {Zero = 0, One = 0, Two = 0}
     writeln(E.Two); // Zero!
 }
 ```


  True, but if you want it be useful they really need to be unique.
Apr 19 2022
prev sibling parent Manfred Nowak <svv1999 hotmail.com> writes:
On Sunday, 17 April 2022 at 18:25:32 UTC, Bastiaan Veelo wrote:

 The reason is in [17.1.5](https://dlang.org/spec/enum.html): 
 “EnumBaseType types cannot be implicitly cast to an enum type.”


Thy. That's the anchor in the specs preventing Enums to be 
integral types.
Apr 19 2022