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?

Thanks!

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?
> 
> Thanks!

Probably not quite what you are looking for but you could use AAs.

Something like:

int foo[char[]];
...
if ("hello" in foo)

Oliver

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

okibi schrieb:
> 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?
> 
> Thanks!

*untested*

bool isOneOf(T)( T value, T[] compares ... ){
	foreach( c; compares ){
		if( value == c ) return true;
	}
	return false;
}
if ( isOneOf( value, 1, 2, 3 ))
    dosomething();

On Tue, 11 Mar 2008 06:45:14 -0400, 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?

Without thinking too deeply about it, you could use this technique ...

bool[int] goodvalues;
static this()
{
    goodvalues = [1:true, 2:true, 3:true];
}
.
.
.
   if (value in goodvalues)
      dosomething();


-- 
Derek Parnell
Melbourne, Australia
skype: derek.j.parnell

Frank Benoit Wrote:

> okibi schrieb:
> > 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?
> > 
> > Thanks!
> 
> *untested*
> 
> bool isOneOf(T)( T value, T[] compares ... ){
> 	foreach( c; compares ){
> 		if( value == c ) return true;
> 	}
> 	return false;
> }
> if ( isOneOf( value, 1, 2, 3 ))
>      dosomething();

This is what I was looking for, thanks!

Is there any chance of the in [] method getting into D or is it a definite no?

okibi wrote:
> Frank Benoit Wrote:
> 
>> okibi schrieb:
>>> 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?
>>>
>>> Thanks!
>> *untested*
>>
>> bool isOneOf(T)( T value, T[] compares ... ){
>> 	foreach( c; compares ){
>> 		if( value == c ) return true;
>> 	}
>> 	return false;
>> }
>> if ( isOneOf( value, 1, 2, 3 ))
>>      dosomething();
> 
> This is what I was looking for, thanks!
> 
> Is there any chance of the in [] method getting into D or is it a definite no?

Probably not much chance, since Walter is one of the ones who thinks A in [x,y,z] should return true if A is 0 1 or 2, regardless of the values of x,y, and z.

See big long argument here:
  http://d.puremagic.com/issues/show_bug.cgi?id=1323

But Walter has been known to change his mind on occasion.

--bb

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!

 --downs

On Tue, 11 Mar 2008 13:39:55 +0100, downs wrote:
> There's a better way actually.
But that is only good for ranges ;-)

Not so good for ...

  if value in set(2,4,7,10,23,445)

I'm pretty sure this will be simple to organize once AST macros are implemented.

-- 
Derek Parnell
Melbourne, Australia
skype: derek.j.parnell

Reply to Derek,

> On Tue, 11 Mar 2008 13:39:55 +0100, downs wrote:
> 
>> There's a better way actually.
>> 
> But that is only good for ranges ;-)
> 
> Not so good for ...
> 
> if value in set(2,4,7,10,23,445)
> 
> I'm pretty sure this will be simple to organize once AST macros are
> implemented.
> 

struct _Set(T) {
 T[] set;
 bool opIn_r(U)(U u) {
   foreach(v; set) if(v==u) return true;
   return false;
 }
}

struct Set {
 static _Set!(T) opIndex(T, U)(T[] a...) {
   _Set!(T) ret;
   ret.set = a.dup; //need the dup???
   return ret;
 }
}

I /think/ that will work. But I haven't tested it.

if(1 in Set[1,2,3,5,9,23])