Skip to content


Context and Problem Statement

1) The .NET runtime uses string to represent a path. This goes against nominal typing.

2) Different platforms support different path separators. This makes path creation difficult and prevents using hardcoded paths.

3) Case sensitivity is dependent on the platform and file system.

OS Separator Character Alternative Separator Character
Windows \\ /
Unix-based / /
OS File System Case-sensitive
Windows NTFS No when using the Win32 API, Yes when using POSIX.
Linux NTFS3 No by default, can be changed using mount options.
Linux ext4 and other Yes, most POSIX file systems are case-sensitive.
macOS APFS No by default, can be changed with Disk Utility.

Key Observations

The forward slash / can be used across all platforms, while the backwards slash \\ can only be used on Windows. Microsoft recommends using the forward slash / character for cross-platforms applications.

Aside from some edge-cases with POSIX compliant file systems, paths can be considered case-insensitive. Having two files with the same name in the same folder that differ only in capitalization is an anti-pattern and should not be supported. Archive formats are the biggest culprits of this, and we should recommend that the Nexus Mods Web APIs be updated to reject archives with those files.

Decision Outcome

Directory Separator Character

Paths must use the forward slash / as the only directory separator character.

Root Directories

Root directories are the only directories that are allowed to end with a directory separator character:

  • Windows: C:/
  • Unix-based: /

The parent directory of a root directory is always the root directory itself, signaling to any consumer that this is the top of the path hierarchy.

Only classic Windows paths that start with a drive letter are supported. UNC paths or anything else is not supported .

Path Sanitization

Raw paths that haven't been created programatically but were provided by the OS or by the User, are considered unsanitized and must be sanitized before they can be used.

Sanitization involves the following process:

  1. Remove trailing whitespaces.

  2. Remove trailing directory separator characters.

  3. On Windows: replace backwards slashes with forwards slashes.

Paths containing relative dots (..) are always considered unsanitized and shall not be resolved in code.

Value Objects

Value objects shall be used for paths.


AbsolutePath represents a fully rooted path, meaning it starts with a root directory and contains a required Directory part and an optional FileName part. Examples:

Full Path Directory FileName
/ / <empty string>
/foo / foo
/foo/bar /foo bar
C:/ C:/ <empty string>
C:/foo C:/ foo
C:/foo/bar C:/foo bar

The Directory part must not end with a directory separator character, unless it's a root directory.


RelativePath represents a non-rooted part of a path. Examples:

  • <empty string>
  • foo
  • foo/bar

A RelativePath can be nested multiple directories deep (eg: foo/bar/baz) and can be hardcoded.