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Reference: KeyPaths

Dracon uses KeyPaths internally to reference specific locations within a nested configuration structure during composition and interpolation. Understanding KeyPaths is essential for using features like value references (@), merge targets (@), include sub-key targeting (@), and deferred paths.

Syntax

KeyPaths use dot (.) notation as the primary separator, with special characters for root, parent navigation, and pattern matching:

  • Segment Separator (.): Separates keys in mappings or indices in sequences.
  • Example: database.host, users.0.name
  • Absolute Root (/): When used only at the beginning of a path, it indicates the path starts from the absolute root of the configuration document being processed. It is not used as a separator between segments.
  • Example: /app/name (Incorrect!), /app.name (Correct), /services.0.port (Correct)
  • Parent (..): Navigates one level up in the hierarchy. Can be chained (... for two levels up, etc.). These are often resolved during path simplification (e.g., a.b..c becomes a.c).
  • Example: config.database..timeout (accesses timeout sibling of database)
  • Current (.): Represents the current level. Often used implicitly for relative paths in interpolation, e.g., ${@.sibling} refers to a sibling key. A leading . like .!include .sibling_file would typically be resolved relative to the current node's location context (often the parent directory).
  • Escaping (\., \/): Use a backslash (\) to escape literal dots (.) or slashes (/) if they appear within a key name itself. This is necessary to distinguish them from separators or the root indicator.
  • Example: section\.with\.dots.value, a.path\/segment.key (References keys named "section.with.dots" and "path/segment" respectively).
  • Wildcards (for Matching Only): Used primarily in patterns like deferred_paths in DraconLoader or potentially custom logic. Not used for direct value retrieval via @.
  • *: Matches any single segment name/index (e.g., a.*.c matches a.b.c).
  • **: Matches zero or more consecutive segments (e.g., a.**.d matches a.d, a.b.d, and a.b.c.d).
  • Partial segment matching with * is also supported within patterns (e.g., a.b*.c matches a.b.c and a.bcd.c).

Separator is . not /

Remember that / denotes the absolute root. All subsequent levels in the path must be separated by dots (.). a/b/c will actually simplify to /c ; when what you probably meant was a.b.c.

Usage in Dracon

KeyPaths are the standard way to target nodes in various Dracon features:

  1. Value References (@ in ${...}):

    • ${@/path.from.root}: Absolute KeyPath.
    • ${@.sibling_key}: Relative KeyPath (sibling).
    • ${@../parent.key}: Relative KeyPath (navigating up).
    • Example: ${@/database.host}, ${@.name}
    • See Interpolation Syntax.

  2. Merge Targets (<<...@target_path:):

    • target_path is a relative KeyPath from the mapping containing the merge key.
    • Example: <<{+<}@database: *db_defaults (merges into the database key).
    • See Merge Key Syntax.

  3. Deferred Paths (DraconLoader(deferred_paths=...)):

    • List of absolute KeyPath patterns (supporting *, **) identifying nodes to defer automatically.
    • Example: ['/services.*.connection', '/external_apis/**']
    • See Deferred Execution Guide.

  4. Include Sub-key Targeting (!include source@target_path):

    • target_path is a KeyPath within the source document.
    • Example: !include file:settings.yaml@database.host (loads only the host value).
    • See Include Syntax.

Internal Representation & Simplification

While you typically interact with KeyPaths as strings, Dracon internally parses them into a list of segments and special tokens (like ROOT, UP). It performs simplification before using them for lookups or matching, resolving . and .. segments where possible (e.g., a.b..c simplifies to a.c, /a/b simplifies to /b). You generally don't need to worry about this unless debugging complex path issues.