R – Why do you need $ when accessing array and hash elements in Perl

arrayshashperlsigils

Since arrays and hashes can only contain scalars in Perl, why do you have to use the $ to tell the interpreter that the value is a scalar when accessing array or hash elements? In other words, assuming you have an array @myarray and a hash %myhash, why do you need to do:

$x = $myarray[1];
$y = $myhash{'foo'};

instead of just doing :

$x = myarray[1];
$y = myhash{'foo'};

Why are the above ambiguous?

Wouldn't it be illegal Perl code if it was anything but a $ in that place? For example, aren't all of the following illegal in Perl?

@var[0];
@var{'key'};
%var[0];
%var{'key'};

Best Answer

Slices aren't illegal:

@slice = @myarray[1, 2, 5];
@slice = @myhash{qw/foo bar baz/};

And I suspect that's part of the reason why you need to specify if you want to get a single value out of the hash/array or not.

Related Solutions

Ruby – the “right” way to iterate through an array in Ruby

This will iterate through all the elements:

array = [1, 2, 3, 4, 5, 6]
array.each { |x| puts x }

Prints:

This will iterate through all the elements giving you the value and the index:

array = ["A", "B", "C"]
array.each_with_index {|val, index| puts "#{val} => #{index}" }

Prints:

A => 0
B => 1
C => 2

I'm not quite sure from your question which one you are looking for.

C# – How to convert a byte array to a hexadecimal string, and vice versa

You can use Convert.ToHexString starting with .NET 5.
There's also a method for the reverse operation: Convert.FromHexString.

For older versions of .NET you can either use:

public static string ByteArrayToString(byte[] ba)
{
  StringBuilder hex = new StringBuilder(ba.Length * 2);
  foreach (byte b in ba)
    hex.AppendFormat("{0:x2}", b);
  return hex.ToString();
}

or:

public static string ByteArrayToString(byte[] ba)
{
  return BitConverter.ToString(ba).Replace("-","");
}

There are even more variants of doing it, for example here.

The reverse conversion would go like this:

public static byte[] StringToByteArray(String hex)
{
  int NumberChars = hex.Length;
  byte[] bytes = new byte[NumberChars / 2];
  for (int i = 0; i < NumberChars; i += 2)
    bytes[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);
  return bytes;
}

Using Substring is the best option in combination with Convert.ToByte. See this answer for more information. If you need better performance, you must avoid Convert.ToByte before you can drop SubString.

Best Answer

Related Solutions

Ruby – the “right” way to iterate through an array in Ruby

C# – How to convert a byte array to a hexadecimal string, and vice versa

Related Topic