New implementation

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Please try to avoid dependencies to third-party libraries and frameworks.

Other implementations
with Ada.Containers.Vectors;
use Ada.Containers;
declare
   function Compare_Function (Left, Right : Item) return Boolean is (Left.P < Right.P);
   
   package Item_Vector_Sorting is new Item_Vectors.Generic_Sorting (Compare_Function);

   use Item_Vector_Sorting;
begin
   Sort (Items);
end;
#include <stdlib.h>
int compareProp (const void *a, const void *b)
{
    return (*(const Item**)a)->p - (*(const Item**)b)->p;
}

qsort(items, N, sizeof(Item*), compareProp);
(sort-by :p items)
#include <algorithm>
std::sort(begin(items), end(items), [](const auto& a, const auto& b) { return a.p < b.p; });
Array.Sort(items, (a, b) => compareFunc(a.p, b.p));
import std.algorithm.sorting;
sort!("a.p < b.p")(items);
items.sort((a, b) => (a.p).compareTo(b.p));
items.sort((a, b) => Comparable.compare(a.p, b.p));
Enum.sort_by(items, &(&1.p))
	
sort_by_birth(ListOfMaps) ->
  lists:sort(
    fun(A, B) ->
      maps:get(birth, A, undefined) =< maps:get(birth, B, undefined)
    end, ListOfMaps).

sort_by_birth(ListOfRecords) -> lists:keysort(#item.birth, ListOfRecords).
import "sort"
less := func(i, j int) bool {
	return items[i].p < items[j].p
}
sort.Slice(items, less)
import "sort"
type ItemPSorter []Item
func (s ItemPSorter) Len() int{ return len(s) }
func (s ItemPSorter) Less(i,j int) bool{ return s[i].p<s[j].p }
func (s ItemPSorter) Swap(i,j int) { s[i],s[j] = s[j],s[i] }

func sortItems(items []Item){
	sorter := ItemPSorter(items)
	sort.Sort(sorter)
}
sortBy (comparing p) items
import qualified Data.List as List
List.sortOn p items
items.sort(function(a,b) {
  return compareFieldP(a.p, b.p);
});
import java.util.Comparator;
items.stream().sorted(Comparator.comparing(x -> x.p))
import java.util.Collections;
import java.util.Comparator;
Collections.sort(items, new Comparator<Item>(){
	@Override
	public int compare(Item a, Item b){
		return a.p - b.p;
	}
});
import java.util.Arrays;
import java.util.Comparator;
Arrays.sort(items, new Comparator<Item>(){
	public int compare(Item a, Item b){
		return a.p - b.p;
	}
});
items.sortedBy { it.p }
(sort #'< items :key #'p)
table.sort(items, function(a,b)
	if a.p < b.p then return true end
end)
function cmp($a, $b)
{
    if ($a->p == $b->p) {
        return 0;
    }

    return ($a->p < $b->p) ? -1 : 1;
}

usort($items, 'cmp');
uses fgl;
type

  TItem = class p: Integer; end;
  TItems = specialize TFPGObjectList<TItem>;

var items: TItems;

  function compare(const a, b: TItem): Integer;
  begin
    Result := a.p - b.p;
  end;

begin
  items := TItems.Create;
  // Add items here.
  items.Sort(@compare);
end.  
@items = sort { $a->{p} cmp $b->{p} } @items;
items = sorted(items, key=lambda x: x.p)
items.sort_by(&:p)
items.sort_by(|a,b|a.p.cmp(&b.p));
items.sort_by_key(|item| item.p);
case class S(x: Int)
val items = List(S(3), S(4), S(2))
items.sortBy( item: S => item.x )