Damn C++ and damn D!

[Jose Armando Garcia]

On Sun, Feb 5, 2012 at 12:57 PM, Timon Gehr <timon.gehr at gmx.ch> wrote:
> On 02/05/2012 03:53 PM, so wrote:
>>
>> On Sunday, 5 February 2012 at 14:24:20 UTC, Timon Gehr wrote:
>>
>>> This should work:
>>>
>>> #define DOTDOTDOT ...
>>>
>>> template<class T> void fun(T a){
>>> if(cond<T>::value) {
>>> auto var = make(a);
>>> DOTDOTDOT;
>>> }else{
>>> auto tmp = make(a);
>>> auto var = make_proxy(tmp);
>>> DOTDOTDOT;
>>> }
>>> }
>>
>>
>> It won't work.
>> You now have two scopes and you have to repeat every line after "var"
>> for both scopes.  Now you have to maintain both of them.
>
>
> You just maintain the macro.
>
>
>> And this grows
>> exponentially for every new condition you have.
>>
>
> It certainly has limits. I completely agree that C++s generic programming
> facilities are severely underpowered.
>

What I would really like to see in D is:

immutable variable = if (boolean_condition)
{
  // initialize based on boolean_condition being true
}
else
{
  // initialize based on boolean_condition being false
}

Scala has this and find it indispensable for functional and/or
immutable programming. Yes, I have been programming with Scala a lot
lately. It has a lot of problem but it has some really cool constructs
like the one above. Scala also has pattern matching and structural
typing but that may be asking too much ;).

I am not sure what it would take to implement this in D but I am
thinking we need the concept of a void type (Unit in scala). Thoughts?