Re: syntatic sugar IN keyword.

Tom McGlynn <>
Thu, 17 Mar 2011 05:41:59 -0700 (PDT)
On Mar 17, 1:11 am, Roedy Green <>

I would like it if you could write:

if ( birthYear == 610
     || birthYear == 1791
     || birthYear == 1851
     || birthYear == 1872 ) )


if ( birthYear in { 610, 1791, 1851, 1872} )

if ( birthYear in SPECIAL_YEARS )

The compiler could be clever. If you said something like this:

if ( i in { 1 , 2 ,3 ,4, 6, 7, 8, 9 } )

It could generate code as

if ( 1 <= i && i <= 9 && i != 5 )

Or it could create a boolean array, or even a map for big lists.

For some cases perhaps you could use something like

    if (in(1,2,3,4,5,6,7,8,9).contains(i)) {...}

with a method

    static Set in(Object... data) {
        Set mySet = new HashSet();
        for (Object element: data) mySet.add(element);
        return mySet;

If you use this a lot you could have this in some Utility class and do
    import static;

That's pretty close to your original request. I think autoboxing will
take care of the primitives but I haven't tried this. You'd need to
be chary of
   if (in(1,2,3...).contains(1.0)) ...

If there were a special syntax it would likely be easier for the
compiler to automatically extract constant <in> lists out of loops but
doing that manually shouldn't be too difficult. There would be harder

   for (somebigloop) {

   method1(x) {
        if (in(1,2,3).contains(x)) ( ...}

where a special syntax would make it a lot easier for the compiler to
recognize the constant expression and compute the hash only one time
rather than for each loop, but in such a case probably the Set should
not be a local variable that needs to be recomputed, but a class

Tom McGlynn

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