Auto returntype

[Alex]

On Monday, 20 May 2019 at 02:32:47 UTC, Alex wrote:
> On Monday, 20 May 2019 at 00:31:48 UTC, sarn wrote:
>> On Sunday, 19 May 2019 at 23:10:08 UTC, Para wrote:
>>> Unless I have very poor reading comprehension, which I might, 
>>> I believe this is already a feature: 
>>> https://dlang.org/spec/function.html#auto-functions
>>
>> The type of an auto function is inferred from the return 
>> argument, but I think Alex wants more sophisticated inference 
>> based on usage.  Maybe something like Hindley-Milner, as used 
>> in Haskell: 
>> http://www.codecommit.com/blog/scala/what-is-hindley-milner-and-why-is-it-cool
>>
>
> Yes, but it's much easier than that. No reason to infer 
> anything. The type is the lvalue's type. but it requires one to 
> determine that the lvalue has a type. In fact, maybe it could 
> be a more general thing where one could simply get the 
> lvalue(see below).
>
>> D's templates could theoretically support more inference, but 
>> that would need
>> 1) Someone interested enough to implement it
>> 2) Someone who can convince Walter that it won't make D's 
>> template system too complicated
>
> First it should be proved to be a sound idea, else it is 
> pointless to do 1 and 2.
>
> ----
>
>
> One could in general get the assignment type and use that in 
> code to perform polymorphic behavior:
>
>
> T foo()
> {
>    writeln(T.stringof);
>    T x;
>    return x;
> }
>
>
> int x = foo();
> float x = foo();
>
> prints
>
> int
> float
>
>
> It requires that the lvalue's type be known and parsed before 
> the template call... not a hard problem but might not be 
> implemented in D as such.

You propose just a new lowering rule for templates, no? If so, 
you just have to list all existent relevant rules (at least here, 
in the forum) and if there aren't any contradictions to the new 
one, chances are, your proposition will be accepted... maybe... :)
The other end of the rod is, that it used to be auto var = 
foo!(type, if any); and not the other way round. This is a 
question of habituation, I think. I mean, the possibility to 
write it in the used way does not vanish, just because a new 
lowering rule is introduced.
And last but not least, readability is subjective. With your 
proposition, you would hide templates as such. Not sure, if this 
is wanted...