Tags

Overview

Extracts and represents metadata annotations from source comments or clang attributes. Enables tag-based filtering and parameterized code generation.

Why Use This?

C++ lacks native reflection. xccmeta extracts custom annotations from two sources to enable opt-in reflection:

1. Comment tags: /// @tag_name(args) — more readable
2. Attribute tags: [[clang::annotate("tag_name")]] — works everywhere, including template/function parameters

Types

Type	Description
tag	Parsed annotation with a name and arguments

Functions

tag()

Default constructor.

tag(name, args)

Construct a tag with a name and argument list.

Signature: tag(const std::string& name, const std::vector<std::string>& args)

Parameters:

• name — tag identifier
• args — list of string arguments

parse (static)

Parse a tag from a string.

Signature: static tag parse(const std::string& to_parse)

Parameters:

• to_parse — string in format "tag_name(arg1, arg2)"

Returns: parsed tag instance

get_name

Get the tag name.

Signature: const std::string& get_name() const

Returns: tag identifier (e.g., "reflect")

get_args

Get the argument list.

Signature: const std::vector<std::string>& get_args() const

Returns: vector of string arguments

get_args_combined

Get arguments as a single comma-separated string.

Signature: std::string get_args_combined() const

Returns: combined args (e.g., "arg1, arg2")

get_full

Get the full tag representation.

Signature: std::string get_full() const

Returns: full string (e.g., "tag_name(arg1, arg2)")

Notes:

• Comment tags (/// @tag) don’t work on template parameters or function parameters (libclang limitation). Use [[clang::annotate("tag")]] for those cases.
• Arguments are simple literals only: no nested parentheses, no named arguments.
• Tags are typically accessed through node methods: has_tag(), find_tag(), get_tags().

Example:

// Comment style
/// @reflect
/// @serialize(binary, version=2)
struct Data {};

// Attribute style
template<typename [[clang::annotate("numeric")]] T>
void process(T value);

// Querying tags
if (node->has_tag("reflect")) {
  auto tag = node->find_tag("serialize");
  if (tag) {
    auto& args = tag->get_args(); // {"binary", "version=2"}
  }
}