C#•14mo ago

✅ Difference between `string[]` and `IEnumerable<string>`

in the following the code, the output seems to be the same:

using System;
using System.IO;

class Program
{
  public static void Main()
  {
    foreach (string dir in Directory.GetDirectories("Settings"))
      Console.WriteLine(dir);
    
    foreach (string dir in Directory.EnumerateDirectories("Settings"))
      Console.WriteLine(dir);
  }
}

using System;
using System.IO;

class Program
{
  public static void Main()
  {
    foreach (string dir in Directory.GetDirectories("Settings"))
      Console.WriteLine(dir);
    
    foreach (string dir in Directory.EnumerateDirectories("Settings"))
      Console.WriteLine(dir);
  }
}

using System;
using System.IO;

class Program
{
  public static void Main()
  {
    foreach (string dir in Directory.GetDirectories("Settings"))
      Console.WriteLine(dir);
    
    foreach (string dir in Directory.EnumerateDirectories("Settings"))
      Console.WriteLine(dir);
  }
}

using System;
using System.IO;

class Program
{
  public static void Main()
  {
    foreach (string dir in Directory.GetDirectories("Settings"))
      Console.WriteLine(dir);
    
    foreach (string dir in Directory.EnumerateDirectories("Settings"))
      Console.WriteLine(dir);
  }
}

i know that

enum

enum

s are used to define a set of exhaustive types, and are closely related to

int

int

s.
but what does it mean to have

IEnumerable<string>

IEnumerable<string>

and how different is it from

string[]

string[]

ero•11/11/24, 7:28 AM

GetDirectoriesGetDirectories returns a complete collection. all items have been evaluated and transformed.
EnumerateDirectionariesEnumerateDirectionaries yields every result back to you one by one. you can use it if you don't want to go over every single result; for example when you're looking for just one specific directory. when you breakbreak in the loop over EnumerateDirectoriesEnumerateDirectories, it won't continue searching for the next result.

ero•11/11/24, 7:28 AM

EnumerateDirectoriesEnumerateDirectories is an iterator method

MODiX•11/11/24, 7:32 AM

ero

REPL Result: Success

const int Length = 3;

static int[] M1()
{
  var ret = new int[Length];

  for (int i = 0; i < Length; i++)
  {
    Console.WriteLine($"M1: {i}");
    ret[i] = i;
  }

  return ret;
}

static IEnumerable<int> M2()
{
  for (int i = 0; i < Length; i++)
  {
    Console.WriteLine($"M2: {i}");
    yield return i;
  }
}

foreach (var i in M1())
  break;

foreach (var i in M2())
  break;

const int Length = 3;

static int[] M1()
{
  var ret = new int[Length];

  for (int i = 0; i < Length; i++)
  {
    Console.WriteLine($"M1: {i}");
    ret[i] = i;
  }

  return ret;
}

static IEnumerable<int> M2()
{
  for (int i = 0; i < Length; i++)
  {
    Console.WriteLine($"M2: {i}");
    yield return i;
  }
}

foreach (var i in M1())
  break;

foreach (var i in M2())
  break;

Console Output

M1: 0
M1: 1
M1: 2
M2: 0

M1: 0
M1: 1
M1: 2
M2: 0

Compile: 577.671ms | Execution: 99.265ms | React with ❌ to remove this embed.

ero•11/11/24, 7:32 AM

it's a bit confusing if you don't know what's going on

Eero `GetDirectories` returns a complete collection. all items have been evaluated an...

tommyOP•11/11/24, 9:02 AM

what i have gathered from this is that there's a difference in the iteration: EnumerateDirectoriesEnumerateDirectories will iterate over the directories one by one to match a condition's expression, whereas GetDirectoriesGetDirectories will iterate over all the files/directories first, provide a

string[]

string[]

over which we iterate

FusedQyou•11/11/24, 9:06 AM

Yes so essentially EnumerateDirectoriesEnumerateDirectories doesn't do anything until you call ToArrayToArray/ToListToList, at which it will start to actually perform the logic and enumerate

FusedQyou•11/11/24, 9:06 AM

Meaning that you can do this multiple times and it will return the current state. This is often a pitfall for developers using IEnumerableIEnumerable because they do not realize that they enumerate multiple times

FusedQyou•11/11/24, 9:07 AM

It's a very generic way to enumerate something because it simply specifies a method to get the current item and to go to the next one, so you can wrap it in many things

FusedQyou•11/11/24, 9:08 AM