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c#async-awaittasklazy-loadingienumerable

How to change the lazy result of Directory.EnumerateFiles in C#


I need to change the lazy result of Directory.EnumerateFiles in C#

I tried the below code but I lost the lazzy behaviour of the Directory.EnumerateFiles function.

public Task<IEnumerable<string>> EnumerateStorageFiles(
    string DirectoryPathOnStorage, string SearchPattern = "*.*")
{
    try
    {
        List<string> result = Directory.EnumerateFiles(
            GetStorageRelatedPath(DirectoryPathOnStorage), SearchPattern,
            new EnumerationOptions()
            {
                IgnoreInaccessible = true,
                RecurseSubdirectories = true,
                AttributesToSkip = FileAttributes.System,
                ReturnSpecialDirectories = false
            }).ToList();

        for (int i = 0; i < result.Count; i++)
        {
             result[i] = Path.GetRelativePath(StorageBasePath, result[i]);
        }

        return Task.FromResult(result.AsEnumerable());
    }
    catch { }

    return Task.FromResult(Enumerable.Empty<string>());
}

Solution

  • public Task <IEnumerable <string>> EnumerateStorageFiles(
      string DirectoryPathOnStorage,
      string SearchPattern = "*.*") {
      try {
        // Using Select to transform paths lazily without converting to List
        IEnumerable <string> result = Directory.EnumerateFiles(
            GetStorageRelatedPath(DirectoryPathOnStorage),
            SearchPattern,
            new EnumerationOptions() {
              IgnoreInaccessible = true,
                RecurseSubdirectories = true,
                AttributesToSkip = FileAttributes.System,
                ReturnSpecialDirectories = false
            })
          .Select(file => Path.GetRelativePath(StorageBasePath, file));
    
        return Task.FromResult(result);
      } catch (Exception ex) {
        //pls do smth
      }
    
      return Task.FromResult(Enumerable.Empty <string>());
    }
    

    The reason you're losing the lazy behavior in your code is because of the .ToList() call on Directory.EnumerateFiles. When you call .ToList(), it immediately forces the enumeration to happen, which means all the files are loaded into memory at once, defeating the purpose of lazy evaluation.

    To maintain the lazy evaluation while transforming the results, you can avoid converting to a list.

    Instead, you can use LINQ to apply transformations lazily while preserving the IEnumerable<string> behavior.

    Reference: https://stackoverflow.com/a/31352719/7676905