The CRTP Design Pattern

A comprehensive guide to using the ebmlTypeCRTP and ebmlElementCRTP mixin templates.

This page provides detailed usage guidelines for implementing your own EBML element types and instances using the library's Curiously Recurring Template Pattern (CRTP) mixins.

The Purpose of the CRTP Mixins

The ebmlTypeCRTP and ebmlElementCRTP templates work together to provide compile-time type safety and automatic pointer conversions. By inheriting from these templates, your custom EBML types gain all the necessary decoding, encoding, and instance creation functionality without the need for manual casting.

Usage Guidelines

To create a paired EBML element type and instance:

• Element Type:
  • Define your element type class (ebmltype_t) to inherit from: ebml::ebmlTypeCRTP<ebmltype_t, ebmlinst_t, typebase_t> where the default typebase_t is ebml::ebmlElementType.
• Element Instance:
  • Define your element instance class (ebmlinst_t) to inherit from: ebml::ebmlElementCRTP<ebmltype_t, ebmlinst_t, instbase_t> where the default instbase_t is ebml::ebmlElement.
  • Both ebml::ebmlTypeCRTP<ebmltype_t, ebmlinst_t, typebase_t> and ebml::ebmlElementCRTP<ebmltype_t, ebmlinst_t, instbase_t> must be friend classes to ebmltype_t.

Required Implementations

To integrate proper decoding and cloning, the following must be implemented:

• Construction and Decoding:
  • A constructor of the form: ebmlinst_t::ebmlinst_t(const ebmltype_t*)
  • For decoding from an ebml::parseString:
    • Either implement:
      • A constructor: ebmlinst_t::ebmlinst_t(const ebmltype_t*, const ebml::parseString&) or
      • A member function: ebmlinst_t::_init(const ebml::parseString&)
    • Optionally, add a _cinit(const ebml::parseString&) for constructing a const instance.
• Decoding From Files:
  • (Optional) For direct decoding from ebml::parseFile (instead of converting it to ebml::parseString), implement:
    • Either a constructor: ebmlinst_t::ebmlinst_t(const ebmltype_t*, const ebml::parseFile&) or
    • A member function: ebmlinst_t::_init(const ebml::parseFile&)
    • Optionally, implement _cinit(const ebml::parseFile&) for decoding into a const instance.
• Cloning:
  • Either provide a copy constructor: ebmlinst_t::ebmlinst_t(const ebmlinst_t&) or implement an internal clone method: ebmlinst_t::_clone(const ebmlinst_t&).
• Encoding Support:
  • Implement the following member functions (if not already handled by the CRTP mixin):
    • ebmlinst_t::dataSize(char*)
    • ebmlinst_t::_encode(char*)