Is typedef an alien?

[language_fan]

Thu, 24 Sep 2009 19:44:09 +0000, language_fan thusly wrote:

> Thu, 24 Sep 2009 15:33:38 -0400, Jarrett Billingsley thusly wrote:
> 
>> On Thu, Sep 24, 2009 at 2:36 PM, Aenigmatic <procode at adam-dott-com.au>
>> wrote:
>>> No further response to any responses to my previous post's responses
>>> is a both swift and non-invasive.
>>>
>>> Now my deeply thought question is ...
>>>
>>> Is typedef (in D) a C/C++ legacy or is the dear orphan now adopted as
>>> a first-class citizen in the US of D?
>> 
>> It's a different beast, and in my experience, pretty useless. Most of
>> the time you want typedef'ed types to interact with other types a
>> little more richly. Say you want to use a double as a time. Okay, what
>> do you get when you subtract two points in time? Not a time, that's for
>> sure. You get a time _span_ instead. So you end up implementing them as
>> structs.
>> 
>> Virtually every time I've tried to use typedef, it hasn't sufficed and
>> I've ended up using a struct instead. It seems like a failed idea, or
>> at the very least, yet another half-thought-out abandoned feature.
> 
> I can imagine some uses for it when the type is very simple, and you
> fear that the compiler cannot inline operations on structs. Other than
> that, common mainstream language features like typedefs, variant!(), and
> enums are mere special cases of algebraic datatypes (with some implicit
> syntactic sugar). There are some downsides, too, but I prefer to have
> the more general type in languages that I use.

If I recall correctly, one of the reasons that also make typedefs in D a 
bit more useless is the inconsistency in implicit casts. E.g. when you 
create a temperature type, I think some of the conversions between 
floats, Temperature, and literals fail.