How to do an in-place `expand` on a domain in Chapel

Question

The expand command in Chapel returns a new domain. I would like to increase a domain by one kinda like

var d: domain(1) = {1..5};
writeln(d);
 --{1..5}
expand(d)(1);
writeln(d);
 --{1..6};

Answer 1

As of Chapel 1.15 there is no in-place option for the expand method on domains. You would need to assign the result of expand to the desired domain:

var eDom = {1..5};
eDom = eDom.expand(1);
writeln(eDom); // {0..6}

It doesn't sound like expand is what you want though, because expand will grow the domain in both directions in each dimension. To add one index to a rectangular domain, you can assign a domain literal to your domain:

var rDom = {1..5};
const hi = rDom.last + 1;
rDom = {rDom.first..hi};
writeln(rDom); // {1..6}

For irregular domains you can use the add method:

var aDom = {1, 3, 5, 7}; // an associative domain
aDom.add(9);
writeln(aDom.sorted()); // 1 3 5 7 9

Note that you cannot use the add method on rectangular domains. This is defined in section 19.8.6 in version 0.983 of the Chapel language specification.

Answer 2

A few online experiments on domain expansion:

some worked as documented, some not:

var      d: domain(1) = {1..5};
writeln( d );                      // SET {1..5}
//      {1..5}

var      e: domain(1) = d.expand(1);
writeln( e );                      // OK, DOMAIN d == {1..5} EXTENDED ON BOTH ENDS INTO {0..6}
//      {0..6}

var      AonD: [d] int;
         AonD.push_back(1);
writeln( AonD.domain );            // OK, DOMAIN EXTENDED INDIRECTLY ON DESIRED END INTO {1..6}
//      {1..6}

// var      f: domain(1) = {1..5}; // NEW {1..5} - A NON-SHARED, NON-USED ( NON-MAPPED ) DOMAIN
//          f.add(6);              // FAILS v/s A PROMISE IN: http://chapel.cray.com/docs/master/builtins/internal/ChapelArray.html#ChapelArray.add
//          f  += 6;               // FAILS
// writeln( f );