Damn C++ and damn D!

[Timon Gehr]

On 02/05/2012 04:17 PM, Jose Armando Garcia wrote:
> 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?

immutable variable = (boolean_condition) ? {
     // initialize based on boolean_condition being true
}():{
     // initialize based on boolean_condition being false
}();