What is the reasoning behind the lack of conversions when passing parameters

[Richard (Rikki) Andrew Cattermole]

On 06/02/2024 11:17 PM, Atila Neves wrote:
> On Tuesday, 6 February 2024 at 10:10:32 UTC, FeepingCreature wrote:
>> On Monday, 5 February 2024 at 09:04:23 UTC, Atila Neves wrote:
>>> On Saturday, 3 February 2024 at 03:19:00 UTC, Walter Bright wrote:
>>>> [...]
>>>
>>> It got bad enough in C++ that the guideline is now to use explicit on 
>>> single parameter constructors: 
>>> https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rc-explicit
>>
>> I just don't think that "this feature can be abused" is a convincing 
>> argument. So what? Make it opt-in, mark it as dangerous, then when 
>> people use it it's on them.
>>
>> I don't want implicit conversion to always be enabled, I want it to be 
>> enabled by a keyword or UDA. @implicit or something. Even 
>> per-parameter would be useful!
> 
> Sure, this would definitely help. I think the lesson learned there is 
> that implicit conversions *by default* are a bad idea. I don't even like 
> integer conversions, cast if you want it.
> 
>> Honestly, if you just hardcoded implicit construction for 
>> `std.sumtype.SumType` I would be quite happy already.
> 
> Something I've wanted every time I've used it.

+1 to all of this.

The implicit conversion wouldn't be too hard to implement either.

I actually implemented an implicit conversion today, in preparation of 
sumtypes!

https://github.com/dlang/dmd/pull/16161

To make the following work:

```d
Enum varF2 = identity(:Middle);

Enum identity(Enum e) {
	return e;
}

enum Enum {
	Middle
}
```