Error while generate DNA with uniform()

[Steven Schveighoffer]

On 9/3/22 8:09 AM, Salih Dincer wrote:
> Hi All,
> 
> We discovered a bug yesterday and reported it:
> 
> https://forum.dlang.org/thread/mailman.1386.1662137084.31357.digitalmars-d-bugs@puremagic.com 
> 
> 
> You know, there is `generate()` depend to `std.range`. It created the 
> error when we use it with the value of an enum. Which get their values 
> from an `enum DNA`, we have 4 members that we want to generate 32 pieces 
> randomly like this:
> 
> ```d
> import std;
> void main()
> {
>    enum DNA { timin = 84,
>               sitozin = 67,
>               guanin = 71,
>               adenin = 65
>             }
>    char[] gene;
>    enum n = 32;
>    auto range = generate!(() => uniform(DNA.min, DNA.max)).take(n);/*
>    auto preferred = generate!(() =>
>                     uniform!"[]"(DNA.min,
>                                  DNA.max)).take(n);//*/

I'm not sure why this doesn't work. First, I would change your enum to 
this (for correctness and readability):

```d
   enum DNA : char { timin = 'T',
              sitozin = 'C',
              guanin = 'G',
              adenin = 'A'
            }
```

There is probably a bug in generate when the element type is an `enum` 
which somehow makes it const. But what you need anyway is a `char`, so 
just return a `char`. For that, you need to specify the return type, 
which requires a different kind of function literal:

```d
    auto preferred = generate!(function char() =>
                     uniform!"[]"(DNA.min,
                                  DNA.max)).take(n);
```

That works.

-Steve