Namespaced maps


A common usage of namespaced keywords and symbols is in providing attribute disambiguation in map contexts:

The namespaces provide value (disambiguation) but have the downside of being repetitive and verbose.

Namespaced maps are a reader (and printer) feature to specify a namespace context for a map.

  • Namespaced maps combine a default namespace with a map and yield a map.

  • Namespaced maps are reader macros starting with #: or #::, followed by a normal map definition.

    • #:sym indicates that sym is the default namespace for the map to follow.

    • #:: indicates that the default namespace auto-resolves to the current namespace.

    • #::sym indicates that sym should be auto-resolved using the current namespace's aliases OR any fully-qualified loaded namespace.

      • These rules match the rules for auto-resolved keywords.

  • A namespaced map is read with the following differences from normal maps:

    • A keyword or symbol key without a namespace is read with the default namespace as its namespace.

    • Keys that are not symbols or keywords are not affected.

    • Keys that specify an explicit namespace are not affected EXCEPT the special namespace _, which is read with NO namespace. This allows the specification of bare keys in a namespaced map.

    • Values are not affected.

    • Nested map keys are not affected.

  • The edn reader supports #: but not #:: with the same rules as above.

  • Maps will be printed in namespaced map form only when:

    • All map keys are keywords or symbols

    • All map keys are namespaced

    • All map keys have the same namespace


Patch: clj-1910-2.patch

Screener notes:

  • Autoresolution supports fully-qualified loaded namespaces (like auto-resolved keywords)

  • TODO: pprint support for namespaced maps

  • TODO: printer flag to suppress printing namespaced maps





Alex Miller


Alex Miller





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