driver_concepts.hpp File Reference

C++20 concept defining the Driver interface contract. More...

#include "epaper/core/errors.hpp"
#include "epaper/drivers/driver.hpp"
#include <concepts>
#include <cstddef>
#include <expected>
#include <span>

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Namespaces
namespace	epaper

Concepts
concept	epaper::Driver

Detailed Description

C++20 concept defining the Driver interface contract.

Uses modern C++ concepts to specify the required interface for display drivers. Provides compile-time validation that driver implementations satisfy the contract.

Design Philosophy:

Concept-Based Polymorphism (C++20)
├─ Compile-Time Validation: Errors caught at instantiation, not runtime
├─ Zero Overhead: No vtables, no dynamic dispatch
├─ Duck Typing: If it walks like a driver and quacks like a driver...
└─ Template Constraints: Display<Driver> only compiles for valid drivers

Benefits Over Virtual Interfaces:

• No runtime cost (no vtable pointer, no virtual dispatch)
• Better inlining opportunities (all calls known at compile time)
• Stronger type safety (type mismatches caught at compile time)
• Clearer error messages (constraint violations are explicit)

Required Driver Interface:

class MyDriver {
public:
  // Lifecycle (returns std::expected<void, Error>)
  auto init(DisplayMode mode) -> std::expected<void, Error>;
  auto sleep() -> std::expected<void, Error>;
  auto wake() -> std::expected<void, Error>;
 
  // Drawing (returns std::expected<void, Error>)
  auto clear() -> std::expected<void, Error>;
  auto display(std::span<const std::byte> buffer) -> std::expected<void, Error>;
 
  // Dimensions (const or static, returns size_t or convertible)
  auto width() const -> std::size_t;
  auto height() const -> std::size_t;
};

Movability Requirement:

• Driver must be std::movable (no manual resource management for move)
• Enables returning drivers from factory functions
• Move semantics used by Display to store driver instance

Validation Example:

// Compile-time check
static_assert(Driver<EPD27>);         // OK - EPD27 satisfies concept
static_assert(Driver<MockDriver>);    // OK - MockDriver satisfies concept
// static_assert(Driver<int>);        // ERROR - int doesn't satisfy Driver
 
// Use in template constraints
template <Driver D>
class Display { ... };  // Only accepts types satisfying Driver concept

See also

Display, driver_traits, EPD27, MockDriver