ToString: enum ⇒ switch

The ToString example is the canonical demonstration of anchor-based triggering and inline injection. It generates a std::string_view toString(EnumType e) function for any enum you annotate, placing the implementation in a .g.cpp file and injecting the declaration back into the header.

What it produces

Given:

include/color.h

// [[codegen::generated::ToString::qualified::Color]]
enum class Color { Red, Green, Blue };

The engine produces:

include/color.h: anchor comment replaced by declaration:

include/color.h (after generation)

std::string_view toString(Color e);
enum class Color { Red, Green, Blue };

generated/include/color.g.cpp: implementation:

color.g.cpp

#include <string_view>

std::string_view toString(Color e)
{
    switch (e)
    {
        case Color::Red:   return "Red";
        case Color::Green: return "Green";
        case Color::Blue:  return "Blue";
        default: return "<unknown>";
    }
}

The qualified modifier

The anchor comment path ::qualified::Color instructs the rule to use the fully-qualified enum name (Color) for the generated function signature. For nested enums in namespaces:

// [[codegen::generated::ToString::qualified::network::Status]]
namespace network {
    enum class Status { Ok, Timeout, Refused };
}

Produces std::string_view toString(network::Status e).

The rule scripts

See the Quick Start for the full script listings. The key behaviors:

• Preamble emits #include <string_view>.
• Transformation collects node.enumerators, builds one case per enumerator, wraps in a switch, and returns { source = impl, inline = { { source = decl } } }.
• Scoped vs unscoped: node.isScoped controls whether case values use the EnumName:: prefix.
• No grouping script: 1:1 routing: one header ☛ one .g.cpp.

Extending this rule

Add a reverse fromString: Return a second item in the inline list and a second function body in source.

Handle explicit values: node.enumerators[].value contains the explicit value as a source text string when set. Use it to make the switch exhaustive under -Wswitch.

Namespace-qualified output: Add a grouping script that routes output to generated/<namespace>/ subdirectories.

Key Takeaways

• Anchor comments trigger rules and control inline injection site.
• The ::qualified::EnumName path segment sets the generated function’s qualified name.
• node.isScoped distinguishes enum class (needs Enum::Value prefix) from plain enum.
• node.enumerators[].value carries explicit enumerator values as source text.
• No grouping script ☛ 1:1 routing. One enum, one .g.cpp.