char.h File Reference

Character-semantics concept and utilities — constexpr-safe character classification and transformation for 1-byte fundamental types. More...

#include <concepts>
#include <type_traits>

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Namespaces
namespace	jh::meta
	Aggregated entry point for compile-time metaprogramming utilities.

Concepts
concept	jh::meta::any_char
	Concept representing character-semantic 1-byte integral types.

Functions
template<any_char Char>
constexpr bool	jh::meta::is_alpha (Char c) noexcept
	Check if character is an alphabetic letter (A-Z, a-z).
template<any_char Char>
constexpr bool	jh::meta::is_digit (Char c) noexcept
	Check if character is a decimal digit (0-9).
template<any_char Char>
constexpr bool	jh::meta::is_alnum (Char c) noexcept
	Check if character is alphanumeric (letter or digit).
template<any_char Char>
constexpr bool	jh::meta::is_hex_char (Char c) noexcept
	Check if character is a valid hexadecimal digit.
template<any_char Char>
constexpr bool	jh::meta::is_base64_core (Char c) noexcept
	Check if character belongs to standard Base64 alphabet.
template<any_char Char>
constexpr bool	jh::meta::is_base64url_core (Char c) noexcept
	Check if character belongs to Base64URL alphabet.
template<any_char Char>
constexpr bool	jh::meta::is_ascii (Char c) noexcept
	Check if character is ASCII.
template<any_char Char>
constexpr bool	jh::meta::is_printable_ascii (Char c) noexcept
	Check if character is printable 7-bit ASCII (range 32-126).
template<any_char Char>
constexpr bool	jh::meta::is_uri_char (Char c) noexcept
	Check if character is a valid URI character (unencoded).
template<any_char Char>
constexpr bool	jh::meta::is_valid_char (Char c) noexcept
	Validate ASCII: reject control chars and DEL, leave non-ASCII untouched.
template<any_char Char>
constexpr char	jh::meta::to_upper (Char c) noexcept
	Convert letter to uppercase; leave others unchanged.
template<any_char Char>
constexpr char	jh::meta::to_lower (Char c) noexcept
	Convert letter to lowercase; leave others unchanged.
template<any_char Char>
constexpr char	jh::meta::flip_case (Char c) noexcept
	Flip case of alphabetic character.

Detailed Description

Character-semantics concept and utilities — constexpr-safe character classification and transformation for 1-byte fundamental types.

Copyright

Copyright 2025 JeongHan-Bae <mastropseudo@gmail.com>
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

Full license: GitHub

Author

JeongHan-Bae <mastropseudo@gmail.com>

This header defines jh::meta::any_char, a C++20 concept identifying the core 1-byte character types (char, signed char, unsigned char), together with a small constexpr-safe classification and transformation toolkit for character operations.

Overview

The any_char concept constrains type parameters to only those built-in 1-byte integral character types directly usable for raw text or binary data. This design ensures type purity, constexpr safety, and clear separation from UTF-8 and byte-level abstractions.

Included utilities

• is_alpha() — check for alphabetic characters (A-Z, a-z).
• is_digit() — check for decimal digits (0-9).
• is_alnum() — check for alphanumeric (letter or digit).
• is_hex_char() — check for valid hexadecimal characters (0-9, A-F, a-f).
• is_base64_core() — check if part of the standard Base64 alphabet (A-Z, a-z, 0-9, '+', '/').
• is_base64url_core() — check if part of the Base64URL alphabet (A-Z, a-z, 0-9, '-', '_').
• is_ascii() — verify whether a character is within the 7-bit ASCII range (0-127).
• is_printable_ascii() — check if character is a printable 7-bit ASCII symbol (32-126 inclusive).
• is_valid_char() — check that character is not a control or DEL (returns true for all non-control bytes).
• to_upper() — convert a letter to uppercase; leave others unchanged.
• to_lower() — convert a letter to lowercase; leave others unchanged.
• flip_case() — invert alphabetic case.

Design rationale

• Concept-level filtering: The any_char constraint rejects higher-level or incompatible types such as char8_t, std::byte, and bool.
• No remove_cvref usage: The concept explicitly expects the raw type form — it models the prototype of character semantics. cv-qualifiers (e.g. const Char) can be manually specified if needed. References are intentionally excluded because Char is a metaprogramming token rather than a forwarding type; templates like template<any_char Char> instantiate with copies, not references, preserving constexpr safety.
• Strict 1-byte validation: Guarantees sizeof(T) == 1 and avoids UB across translation units when hashing or reinterpreting raw data.

Version

1.3.x

Date

2025