This may be is a very basic question, but is there a way to let me omit a repeating variable when doing multiple boolean operations?

if ( var == a || var == b || var == c || var == d)
if ( var == (a || b || c || d) )

Hello Strtr,

> This may be is a very basic question, but is there a way to let me
> omit a repeating variable when doing multiple boolean operations?
> 
> if ( var == a || var == b || var == c || var == d) if ( var == (a || b
> || c || d) )
> 

bool B;
switch(var) { case a,b,c,d: B = true; break; default B = false; break; }
if(B)

or you can put the then/else parts right in the switch

BCS Wrote:

> Hello Strtr,
> 
> > This may be is a very basic question, but is there a way to let me omit a repeating variable when doing multiple boolean operations?
> > 
> > if ( var == a || var == b || var == c || var == d) if ( var == (a || b
> > || c || d) )
> > 
> 
> bool B;
> switch(var) { case a,b,c,d: B = true; break; default B = false; break; }
> if(B)
> 
> or you can put the then/else parts right in the switch
> 

Not really what I had in mind, but works yes.

On Fri, 22 Jan 2010 22:55:45 +0100, strtr <strtr@spam.com> wrote:

> This may be is a very basic question, but is there a way to let me omit a repeating variable when doing multiple boolean operations?
>
> if ( var == a || var == b || var == c || var == d)
> if ( var == (a || b || c || d) )

bool anySame( T, U... )( T arg1, U args ) {
  foreach ( arg; args ) {
    if ( arg1 == arg ) {
      return true;
    }
  }
  return false;
}

bool allSame( T, U... )( T arg1, U args ) {
  foreach ( arg; args ) {
    if ( arg1 != arg ) {
      return false;
    }
  }
  return true;
}

Not tested, but they should work:

if ( anySame( var, a, b, c, d ) ) {
}

if ( allSame( var, a, b, c, d ) ) {
}

-- 
Simen

Simen kjaeraas Wrote:

> 
> Not tested, but they should work:
> 
> if ( anySame( var, a, b, c, d ) ) {
> }
> 
> if ( allSame( var, a, b, c, d ) ) {
> }
> 

A lot prettier.
I thought there would be a generic (basic) solution to this which I just didn't know about but maybe I actually do know the basics by now :)
> -- 
> Simen

On 01/23/2010 12:29 AM, strtr wrote:
> Simen kjaeraas Wrote:
>
>>
>> Not tested, but they should work:
>>
>> if ( anySame( var, a, b, c, d ) ) {
>> }
>>
>> if ( allSame( var, a, b, c, d ) ) {
>> }
>>
>
> A lot prettier.
> I thought there would be a generic (basic) solution to this which I just didn't know about but maybe I actually do know the basics by now :)
>> --
>> Simen
>
If we get opIn_r for arrays, you can do

if (var in [a, b, c, d]) {
}

Which I find a lot prettier.

On Mon, 25 Jan 2010 09:59:42 +0100, Pelle Månsson <pelle.mansson@gmail.com> wrote:

> On 01/23/2010 12:29 AM, strtr wrote:
>> Simen kjaeraas Wrote:
>>
>>>
>>> Not tested, but they should work:
>>>
>>> if ( anySame( var, a, b, c, d ) ) {
>>> }
>>>
>>> if ( allSame( var, a, b, c, d ) ) {
>>> }
>>>
>>
>> A lot prettier.
>> I thought there would be a generic (basic) solution to this which I just didn't know about but maybe I actually do know the basics by now :)
>>> --
>>> Simen
>>
> If we get opIn_r for arrays, you can do
>
> if (var in [a, b, c, d]) {
> }
>
> Which I find a lot prettier.

Is this good enough?

struct CheckIf( T ) {
  T payload;
  bool opIn( T[] rhs ) {
    foreach ( e; rhs ) {
      if ( e == payload ) {
        return true;
      }
    }
    return false;
  }
}

CheckIf!( T ) checkIf( T )( T rhs ) {
  return CheckIf!( T )( rhs );
}

if ( checkIf( true ) in [ false, true, false ] ) {
}

-- 
Simen

Simen kjaeraas Wrote:

> On Mon, 25 Jan 2010 09:59:42 +0100, Pelle MÃ¥nsson <pelle.mansson@gmail.com> wrote:
> 
> > On 01/23/2010 12:29 AM, strtr wrote:
> >> Simen kjaeraas Wrote:
> >>
> >>>
> >>> Not tested, but they should work:
> >>>
> >>> if ( anySame( var, a, b, c, d ) ) {
> >>> }
> >>>
> >>> if ( allSame( var, a, b, c, d ) ) {
> >>> }
> >>>
> >>
> >> A lot prettier.
> >> I thought there would be a generic (basic) solution to this which I
> >> just didn't know about but maybe I actually do know the basics by now :)
> >>> --
> >>> Simen
> >>
> > If we get opIn_r for arrays, you can do
> >
> > if (var in [a, b, c, d]) {
> > }
> >
> > Which I find a lot prettier.
> 
> Is this good enough?
> 
> struct CheckIf( T ) {
>    T payload;
>    bool opIn( T[] rhs ) {
>      foreach ( e; rhs ) {
>        if ( e == payload ) {
>          return true;
>        }
>      }
>      return false;
>    }
> }
> 
> CheckIf!( T ) checkIf( T )( T rhs ) {
>    return CheckIf!( T )( rhs );
> }
> 
> if ( checkIf( true ) in [ false, true, false ] ) {
> }
> 
> -- 
> Simen

Sometimes code just makes me smile :)

On 01/25/2010 10:28 AM, Simen kjaeraas wrote:
> On Mon, 25 Jan 2010 09:59:42 +0100, Pelle Månsson
> <pelle.mansson@gmail.com> wrote:
>
>> On 01/23/2010 12:29 AM, strtr wrote:
>>> Simen kjaeraas Wrote:
>>>
>>>>
>>>> Not tested, but they should work:
>>>>
>>>> if ( anySame( var, a, b, c, d ) ) {
>>>> }
>>>>
>>>> if ( allSame( var, a, b, c, d ) ) {
>>>> }
>>>>
>>>
>>> A lot prettier.
>>> I thought there would be a generic (basic) solution to this which I
>>> just didn't know about but maybe I actually do know the basics by now :)
>>>> --
>>>> Simen
>>>
>> If we get opIn_r for arrays, you can do
>>
>> if (var in [a, b, c, d]) {
>> }
>>
>> Which I find a lot prettier.
>
> Is this good enough?
>
> struct CheckIf( T ) {
> T payload;
> bool opIn( T[] rhs ) {
> foreach ( e; rhs ) {
> if ( e == payload ) {
> return true;
> }
> }
> return false;
> }
> }
>
> CheckIf!( T ) checkIf( T )( T rhs ) {
> return CheckIf!( T )( rhs );
> }
>
> if ( checkIf( true ) in [ false, true, false ] ) {
> }
>
Interesting solution! Very clever!

I still think opIn_r should be defined for arrays, though. :)

Pelle Månsson <pelle.mansson@gmail.com> wrote:

> Interesting solution! Very clever!

Thank you.

> I still think opIn_r should be defined for arrays, though. :)

Yeah, but currently, 'a in b' means '(∃b[a])', that is,
'is a a valid index in b'.
This means having 'a in b' mean '(∃i)( b[i] = a )', that is,
'is there such an i that b[i] == a' would introduce
inconsistencies.

While I do agree it would, I do see reasons for including such
a thing to the language, especially seeing how often just that
question arises, and how rarely the first meaning is actually
useful.

-- 
Simen