boop

Object-oriented programming for bash 4.3+ — real classes, objects, inheritance, and a standard library, in pure bash.

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Taggable (mixin)

Tag, untag, and query arbitrary string labels on any object. Tags are stored in the host object’s descriptor as a comma-separated internal property (_tags). The host class does not need to declare _tags with has:.

Dependencies

. boop Taggable

Mixing In

boopClass Article isa:SomeBase mixin:Taggable has:title,body public:new,...

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Adding Tags

$obj.addTag "urgent"
$obj.addTag "backend" "v2" "reviewed"    # multiple at once
$obj.addTag "urgent"                     # duplicate — silently ignored

Tags are case-sensitive strings. Any non-empty string is a valid tag.

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Querying Tags

$obj.hasTag "urgent" && echo "needs attention"    # exit 0 = has tag
$obj.hasTag "missing" && echo "yes"               # exit 1 — silent

into=all $obj.getTags      # all="urgent,backend,v2,reviewed"
into=n   $obj.tagCount     # n="4"

getTags returns a comma-separated string, or empty string if untagged. tagCount returns an integer count as a string.

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Removing Tags

$obj.removeTag "reviewed"
$obj.removeTag "nonexistent"    # no-op — does not crash

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Identifying the Mixin

into=v $obj.identify    # "Taggable::identify"

Returns the string "Taggable::identify". Used to verify mixin resolution order when multiple mixins provide the same method name. The first mixin listed in boopClass wins; call $obj.Taggable::identify to force Taggable’s version regardless of resolution order.

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Common Patterns

Filtering by tag

# Given a list of object IDs, find those tagged "urgent"
for id in "${objects[@]}"; do
  _Self="$id" Taggable.hasTag "urgent" && urgent_list+=("$id")
done

Tag-based routing

if $task.hasTag "async"; then
  queue_task "$task"
elif $task.hasTag "immediate"; then
  run_now "$task"
fi

Reporting tag inventory

into=tags $obj.getTags
IFS=',' read -ra tag_arr <<< "$tags"
printf "Tags (%d):\n" "${#tag_arr[@]}"
for tag in "${tag_arr[@]}"; do
  printf "  - %s\n" "$tag"
done

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Design Notes

No has: required. Tags go into the descriptor under the _tags key using __boop.set/__boop.get. The leading underscore is a naming convention for internal/private properties that the host class did not declare. This avoids polluting the host class’s declared property list.

Comma separator. Tags are stored as tag1,tag2,tag3. This means commas are not valid characters within a tag value. Any other character is fine.

Conflict resolution. If another mixin also declares identify, the first mixin listed in boopClass wins. Call $obj.Taggable::identify to invoke Taggable’s version explicitly regardless of resolution order.

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