Worst ideas/features in programming languages?

[Timon Gehr]

On 04.01.22 08:52, Walter Bright wrote:
> On 1/3/2022 10:37 PM, Timon Gehr wrote:
>> If `foo(int, int)` is defined to be literally the same as 
>> `foo(int[2])`, there is no conversion. But anyway, I guess you'd also 
>> consider anything that would make this work an "implicit conversion"?
>>
>> double foo(int x,string y);
>>
>> writeln([(1,"2"),(1,"3"),(3,"4")].map!foo);
> 
> Currently, tuples can map right on to argument lists, there is no 
> conversion. This works because a tuple in D isn't really a type at all. 
> It's just a collection of expressions.
> ...

But in the example above, those so-called "tuples" would expand right 
into the array literal and cause an error due to incompatible types. 
This can't work if `(1,"2")` etc. auto-expand. Furthermore, to put them 
into an array, they need to have an address.

> 
>> If so, maybe one way to make _some_ progress on this is to have a DIP 
>> specifically for destructuring, without adding any new types?
> 
> I'm not sure what destructuring,

Currently working with tuples (including actual tuples that are actual 
expressions, e.g., Phobos tuples) is inconvenient mostly (but not only) 
because you can't easily expand them into multiple named variables.

```d
auto (col1, col2) = table.query!((ref 
row)=>tuple(row.column1,row.column2))(key);
```

Proposal 1 here:
https://github.com/tgehr/DIPs/blob/tuple-syntax/DIPs/DIP1xxx-tg.md

Proof-of-concept implementation here:
https://github.com/tgehr/dmd/commit/8ad53b0891d3353dd96711595c06326ac0195d1b
https://github.com/tgehr/dmd/commit/a0f59f93ab3727c93585dc658444860926a4b2c6

> but yes, not adding new types.

That's what I thought, so the tuple DIP is based on lowering to structs.

What's the path forward to making this work?

```d
double foo(int x,string y);

writeln([(1,"2"),(1,"3"),(3,"4")].map!foo);
```

My suggestion was proposal 2 here:
https://github.com/tgehr/DIPs/blob/tuple-syntax/DIPs/DIP1xxx-tg.md

Proof-of-concept implementation here:
https://github.com/tgehr/dmd/commit/bdb40fa96c471a7ace84596511a27ba3e803214f
https://github.com/tgehr/dmd/commit/dad942117d85683e6234ef312c6d59be82f0c3a2

Note that Phobos tuples are implemented using an `alias this` to a 
built-in "tuple" of members:
https://github.com/dlang/phobos/blob/master/std/typecons.d#L636-L655