simple_enum

fmt::format Support for Enumerations

Overview

fmt::format is a part of the {fmt} library, a modern formatting library for C++. The simple_enum library extends fmt::format support to enumerations via a custom formatter specialization, enabling easy and efficient string formatting of enum values using the {fmt} library.

Implementation

To enable fmt::format support for your enumeration types, include the custom formatter specialization provided in simple_enum/fmtlib_format.hpp.

Custom Formatter

The simple_enum/fmtlib_format.hpp header defines a fmt::formatter specialization for enumeration types, leveraging simple_enum::enum_name for converting enum values to their string representations.

#include <fmt/format.h>

template<typename T>
  requires simple_enum::bounded_enum<T>
struct fmt::formatter<T> : fmt::formatter<fmt::string_view> {
  // Formatting logic here
};

• The formatter is defined only for enumerations satisfying simple_enum::bounded_enum (first/last enumerators, simple_enum::info specialization or adl_enum_bounds). Other enumerations, like std::byte, keep formatting provided by {fmt}.
• The format spec is the same as for fmt::string_view (fill, align, width, precision), e.g. fmt::format("{:>10}", value).
• A value without a name is formatted as its underlying integer value, e.g. static_cast<my_enum>(42) gives 42.

Usage

Include the simple_enum/fmtlib_format.hpp in your project to use fmt::format with enumeration types:

#include <simple_enum/fmtlib_format.hpp>

Example Code

#include <iostream>
#include <simple_enum/fmtlib_format.hpp>  // Include custom formatter support
#include <fmt/format.h>

enum class lorem_ipsum_short { eu, occaecat, dolore, first = eu, last = dolore };

int main() {
    // Use fmt::format to format an enum value directly
    std::cout << fmt::format("{}\n", lorem_ipsum_short::eu);  // Outputs: eu
    std::cout << fmt::format("[{:>8}]\n", lorem_ipsum_short::dolore);  // Outputs: [  dolore]
    std::cout << fmt::format("{}\n", static_cast<lorem_ipsum_short>(42));  // Outputs: 42
}

This example demonstrates using fmt::format to format an enumeration value directly to a string, provided the enumeration satisfies simple_enum::bounded_enum and the custom formatter is included.

Requirements

• The {fmt} library must be included in your project.
• Enumerations must satisfy simple_enum::bounded_enum.

Integrating fmt::format support for enums enhances the flexibility and expressiveness of formatting operations in C++ applications, making it easier to incorporate enum values into formatted strings with the efficiency and type safety of the {fmt} library.

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