R – Is Perl guaranteed to return consistently-ordered hash keys

hashkeyperl

Given something like

foreach (keys %myHash) {
   ... do stuff ...
}

foreach (keys %myHash) {
   ... do more stuff ...
}

Is Perl guaranteed to iterate over the keys in a consistent order if the hash is not altered?

Best Answer

Yes. From perldoc -f keys:

The keys are returned in an apparently random order. The actual random order is subject to change in future versions of perl, but it is guaranteed to be the same order as either the values or each function produces (given that the hash has not been modified). Since Perl 5.8.1 the ordering is different even between different runs of Perl for security reasons (see "Algorithmic Complexity Attacks" in perldoc perlsec).

(emphasis mine)

Related Solutions

Javascript – How to find the keys of an object

There is function in modern JavaScript (ECMAScript 5) called Object.keys performing this operation:

var obj = { "a" : 1, "b" : 2, "c" : 3};
alert(Object.keys(obj)); // will output ["a", "b", "c"]

Compatibility details can be found here.

On the Mozilla site there is also a snippet for backward compatibility:

if(!Object.keys) Object.keys = function(o){
   if (o !== Object(o))
      throw new TypeError('Object.keys called on non-object');
   var ret=[],p;
   for(p in o) if(Object.prototype.hasOwnProperty.call(o,p)) ret.push(p);
   return ret;
}

Perl – Are quotes around hash keys a good practice in Perl

Without quotes is better. It's in {} so it's obvious that you are not using barewords, plus it is both easier to read and type (two less symbols). But all of this depends on the programmer, of course.

Best Answer

Related Solutions

Javascript – How to find the keys of an object

Perl – Are quotes around hash keys a good practice in Perl

Related Topic