How Do Transparent Comparators Enhance C 14 Associative Containers?

The Significance of Transparent Comparators

C 14 introduces a distinction known as "transparent comparators" within associative containers. This article delves into the purpose and implications of this concept.

Rationale for Transparent Comparators

The issue presented in Dietmar's and remyabel's answers highlights the limitation of earlier associative containers. They couldn't perform certain operations (e.g., find, count) with types not directly comparable to the container's key type. Transparent comparators address this by enabling the use of a type that can compare with the container's key.

Default Behavior and Compatibility

Transparent comparators do not affect the default behavior of standard containers. The addition of transparent comparator overloads allows you to use them optionally for enhanced flexibility. By default, the containers still operate as before, maintaining backward compatibility.

Transparent Functor Usage

To utilize transparent comparators, simply employ a "transparent functor" like std::less<>, which accepts any argument types. This enables heterogeneous lookup operations.

Naming Justification

The term "transparent comparator" originates from the concept of "diamond operators" introduced in STL's N3421. Transparent functors, essential for associative containers' heterogeneous lookup functionality, forward their arguments to another operator. They resemble diamonds in their ability to connect different argument types, hence the name "transparent comparator."

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