container_traits.h File Reference

Unified deduction model for container element types. More...

#include <ranges>
#include <type_traits>
#include "jh/conceptual/iterator.h"
#include "jh/conceptual/sequence.h"

Go to the source code of this file.

Namespaces
namespace	jh::concepts
	Behavioral concept namespace of the JH Toolkit.

Concepts
concept	jh::concepts::is_contiguous_reallocable
	Concept that constrains types usable in contiguous, reallocating containers.

Typedefs
template<typename C>
using	jh::concepts::container_value_t = typename detail::container_value_type_impl<C>::type
	Deduce the value type of a container C.

Detailed Description

Unified deduction model for container element 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 the trait jh::concepts::container_value_t, a unified and extensible mechanism for deducing the value type of arbitrary container-like types. It harmonizes three deduction strategies — user registration, declared value_type, and iterator-based inference — under a deterministic priority system.

Purpose

Many standard and custom containers expose different or ambiguous value-type information. This trait provides a canonical, conflict-resolving method to obtain a single consistent element type used across the entire jh::concepts subsystem (e.g. in closable_container_for and collectable_container_for).

Deduction priority

1. User override: jh::container_deduction<C>::value_type — explicit registration always takes precedence.
2. Declared type: C::value_type — used if no override is present.
3. Iterator-based deduction: extracted via iterator_t<C> and iterator_value_t<iterator_t<C>>.
4. Conflict resolution: if both declared and deduced forms exist and share a common reference, the declared form wins.
5. Fallback: void — deduction failure.

User customization point

Custom containers can specialize jh::container_deduction<C> to explicitly define a value_type. This mechanism overrides all automatic deduction and provides a stable interface for third-party containers that do not follow standard iterator or value conventions.

Design rationale

• Fully constexpr and SFINAE-safe; compatible with incomplete types.
• Consistent with std::ranges conventions while allowing user extension without ADL or traits injection.
• Provides uniform type deduction across collect, to, and all range-concept meta-utilities.

See also

jh::concepts::iterator_t

jh::concepts::sequence_t

jh::concepts::closable_container_for

jh::concepts::collectable_container_for

Version

1.3.x

Date

2025