Comparing Multiple Values

[Bill Baxter]

downs wrote:
> Bill Baxter wrote:
>> okibi wrote:
>>> I've looked all over the site but can't seem to find if D supports any
>>> kind of like IN statement for comparisons. For example, I can do the
>>> following in SQL:
>>>
>>> select *
>>> from table
>>> where value in (1,2,3)
>>>
>>> And it will compare it to 1, 2, and 3. Is this possible to do within
>>> D's if statement? I hate to go about it as such:
>>>
>>> if (value == 1 || value == 2 || value == 3)
>>>     dosomething();
>>>
>>> Just seems like this could be written better. Can anyone give me any
>>> pointers?
>> I can point you to a bunch of discussions where certain people argued
>> tooth and nail that  "if(value in [1,2,3])" should mean
>> "if(value==0||value==1||value==2)", leading basically to a stalemate.
>> So, no.  Nothing like that is in the language.
>>
>> But you can write a little "contains" function that will do the trick.
>>
>> Or ask Downs how to make "if(x /In/ [1,2,3])" work.
>>
>> --bb
> 
> There's a better way actually.
> 
> import std.stdio;
> 
> // bottom-inclusive, top-exclusive, like slices.
> struct _Range(T) {
>   T from, to;
>   bool opIn_r(U)(U u) {
>     return u < to && u !< from;
>   }
> }
> 
> struct Range {
>   static _Range!(T) opSlice(T, U)(T from, U to) {
>     return _Range!(T)(from, to);
>   }
> }
> 
> void main() {
>   writefln(3 in Range[2..4], " -- ", 4 in Range[2..4]);
> }
> 
> Have funs!

What?! Dost mine eyes deceive me?  Downs just gave up an opportunity to 
proselytize about his infix operators?
This is sure a sign of the end times, my friends.

--bb