PROPOSAL: fold keyword (original) (raw)

Joshua Bloch jjb at google.com
Thu Mar 5 13:28:11 PST 2009

Gabriel,

This doesn't seem compelling.

Here's your simple example:

// sum all numbers in the list
Integer sum =
fold(Integer n : list;     // iterating collection element n
     Integer result = 0) { // Where to accumulate the result, and
         the initial value
         result += n;
     };
}

And here's how it looks today (with no change to the language or libraries):

Integer sum = 0;
for (Integer n : list)
    sum += n;

Here's one of your complex examples:

// returns a new collection with the salaries of the employees not on vacation List salaries = fold(Employee e : emps; List newList = new ArrayList()) { if (!e.onVacation()) { newList.add(e.getSalary()); } }

And here's how it looks today:

 List<BigDecimal> salaries = new ArrayList<BigDecimal>();
 for (Employee e : emps)
     if (!e.onVacation())
         salaries.add(e.getSalary());

To my eyes, the current version is clearer as well as shorter.

        Josh

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