Syntax

	$fun.comparator()

Description

Constructs a comparison function for sort() from an access function which calculates a comparison key from a list element. Sorting a list with such a comparator establishes an order of the values supplied by the access function.

Parameters

Return value

type: Function

A comparison function that can be used for sorting sets and lists.

Examples

Comparison function from an access function

	all(`my.module:MyType`)
  .sort(comparator(x -> $x.get(`my.module:MyType#name`)))

Output: List of all instances of the type my.module:MyType sorted by the values of the attribute name.

Here, the comparator() function makes a comparator function out of the access function x -> $x.get(`my.module:MyType#name`, which returns the value of the property name for a lis element.

Equivalent to the previous example without comparator

	all(`my.module:MyType`)
  .sort(x -> y -> {
    name1 = $x.get(`my.module:MyType#name`);
    name2 = $y.get(`my.module:MyType#name`);
    if ($name1 < $name2, 
      -1, 
      if ($name1 > $name2, 1, 0));
  })

output: List of all instances of the type my.module:MyType sorted by the values of the attribute name.

In the above example, the comparator function is specified directly. Here, the name property must be accessed twice and the (-1, 1, 0) logic of a comparison function is explicitly spelled out. This could also be simplified by using the Comparative value function.