Why typedef's shouldn't have been removed :(

[Steven Schveighoffer]

On Mon, 07 May 2012 15:48:22 -0400, Mehrdad <wfunction at hotmail.com> wrote:

> On Monday, 7 May 2012 at 19:29:26 UTC, Steven Schveighoffer wrote:
>> I think it was more that the whole concept was flawed -- typedef int  
>> myint never really did exactly what you wanted it to.
>>
>> For example:
>>
>> myint m = 1; // ok
>> m += 5; // ok
>> m = m + 5; // error?
>
> It's definitely an error, because 5 isn't myint.
> Of course, it wouldn't be an error in C code, but keeping source  
> compatibility isn't a goal either.

I'm looking at this:

m += 5; // ok
m = m + 5; // error

And thinking, hm.. this is no good :)

C compatibility is not what we are after here, alias already handles C  
compatibility.

> Wouldn't a global search-and-replace that replaced "typedef" with  
> "alias" when porting C code have fixed 99% of this issue, practically  
> speaking?

No, it's not a portability issue.  It's a WTF issue.

>> Things got even worse when you weren't typedef'ing a basic type.
>
> It sounds so trivial to fix though (especially since it's not silent  
> breakage)...
> Would you mind giving another (actual) example (perhaps with a custom  
> type?) that came up, and which shows the extent of the problem and why  
> it was difficult to solve without disallowing typedef entirely?
> I'm having a hard time seeing why the problem was so difficult (or  
> tedious) to fix... a search/replace for typedef/alias would've fixed all  
> (or almost) all the cases when porting C code, right?

I'm almost 100% certain that the issues had nothing to do with C  
compatibility.  It was all in how D typedefs behaved strangely.

Not being one to have used them much, I can only recollect that one  
example.  I do remember people bitching about them quite a bit, and nobody  
really having any good ideas on how to fix them, but I don't know circa  
what time period to look for those discussons.  One person who was an  
ardent supporter of typedefs, and still wants *something* like them is  
bearophile.  He might be able to list some issues/find some old posts/bugs  
that make more sense.

-Steve