E2094 'operator+' not implemented in type 'UnicodeString' for arguments of type 'int'

E2094

program Project6;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils;


function MatchPattern(const pattern, s: string): boolean;
var
  i: integer;
begin
  result := length(pattern) = length(s);
  
  // Add breakpoint here
  // Evaluate or watch variable s[0].
  // Result is "E2094 'operator+' not implemented in type 'UnicodeString' for arguments of type 'int'"
  
  if result then
    for i := 1 to length(pattern) do
      case pattern[i] of
        '#':
          result := result and CharInSet(s[i], ['0'..'9']);
        else
          result := result and (s[i] = pattern[i]);
      end;
end;

begin
  try
    if MatchPattern('####-##-## ##:##', '2007-04-05T14:30') then
      WriteLn('True')
    else
      WriteLn('False');

    Readln;
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.