[onert] Apply c++17 features

[ragmani]

What

Let's apply C++17 features to onert. The goal is to modernize the codebase by leveraging new language features, thereby simplifying the code and improving maintainability.

Why

• Simplification: Modern C++17 features can reduce boilerplate code and improve code readability.
• Maintainability: Using updated syntax and constructs makes it easier to maintain and extend the code in the future.
• Performance & Safety: Some C++17 features can lead to better performance and more robust error handling.
• Consistency: Standardizing the codebase to a modern C++ standard promotes consistency across the project.

Features to be applied

• Nested Namespace Declarations

  • Simplifies deeply nested namespace syntax, reducing verbosity and improving readability.
  • cppreference

• Inline Variables

  • Avoids multiple definition issues by allowing variables to be defined in headers without violating ODR.
  • cppreference

• Structured Bindings

  • Provides a concise way to unpack tuples or struct members, making code cleaner and easier to understand.
  • cppreference

• if constexpr

  • Enables compile-time conditional branching in templates, reducing code complexity and avoiding unnecessary instantiations.
  • cppreference

• Fold Expressions

  • Simplifies the handling of variadic templates by reducing parameter packs with a single expression.
  • cppreference

• Template Argument Deduction for Class Templates (Deduction Guides)

  • Eliminates the need to specify template arguments explicitly when constructing objects, enhancing code brevity.
  • cppreference

• Filesystem Library (std::filesystem)

  • Standardizes file and directory operations, making code more portable and easier to maintain compared to platform-specific APIs.
  • cppreference

• std::optional

  • Offers a safer alternative to pointers or sentinel values for representing optional data, improving code clarity and robustness.
  • cppreference

• std::variant

  • Provides a type-safe union for handling multiple types in a single variable, enhancing code safety and flexibility.
  • cppreference

• std::any

  • Enables storage of any type in a type-safe manner, useful for heterogeneous collections without compromising type safety.
  • cppreference

• std::string_view

  • Allows efficient non-owning views over strings, reducing unnecessary copying and improving performance when handling substrings.
  • cppreference

• Parallel Algorithms (Execution Policies)

  • Facilitates the parallelization of standard algorithms, potentially improving performance on multi-core systems with minimal code changes.
  • cppreference

• [[nodiscard]] Attribute

  • Helps prevent bugs by issuing warnings when important return values are ignored, ensuring that critical results are handled properly.
  • cppreference

[ragmani]

Nested Namespace Declarations

• [onert] Apply nested namespace in api directory. #14642
• [onert] Apply nested namespace in backend directory #14643
• [onert] Apply nested namespace in core directory #14644
• [onert] Apply nested namespace in loader and odc directory #14645

[ragmani]

Inline Variables

• [onert/train] Apply inline variable to the metadata name #14641
• [onert] Apply inline variable to Exectime #14648
• [onert] Apply inline variable to OperandNode #14649
• [onert] Apply inline variable to OperationNode #14650
• [onert] Apply inline variable to Node #14651
• [onert] Apply inline variable to EventWriter #14652
• [onert] Apply inline variable to all other applicable locations #14653
• [cker] Apply inline variables #14655
• [onert] Apply inline variables to tests #14656

[ragmani]

Structured Binding

• [onert] Apply structured binding in ARMComputeEx #14664
• [cker] Apply structured binding in cker #14665
• [onert] Apply structured binding in onert #14672

[ragmani]

if constexpr

• [onert] Apply if constexpr #14675

[ragmani]

fold expressions

• [compute] Apply fold expressions #14677
• [onert] Apply fold expressions #14678

[ragmani]

Template Argument Deduction for Class Templates (Deduction Guides)

This feature could negatively impact readability, so I will not be applying it.

[ragmani]

Filesystem Library (std::filesystem)

This feature was already resolved by #12450

[ragmani]

std::optional

Considering consistency with the existing code and potential performance overhead, I did not find any suitable places to apply std::optional.

[ragmani]

std::variant

• [compute] Apply std::variable to Shape #14679
• [onert] Replace LossParam with std::variant #14681