Traits in C++

In this article, we will discuss about traits in C++. C++ trait is an interesting function and variable inside of which the features and skills of the class are created for runtime. The Characters, which are no longer a common language feature in object-oriented programming languages, are thought of as a group of related functions that make up the behavior or feature of a specific unit. In C++ the traits use template metaprogramming techniques at compile time to generate code units for types that will be used.

In C++ traits can be used to encode very different characteristics, e.g. the number of bits in a quantity, the alignment of a type, or properties specific to different types. This information is then passed to the compiler which takes it as the guidance for code optimization and/or the correctness of error messages.

Traits are the most important features of C++, which help programmers write type-safe, generic, and efficient program. Thus, we will be non-error programmers as well as more agile, extensible and maintainable type of code users.

Common Types of Traits:

Several types of Traits in C++. Some main types of Traits are as follows:

• Type Traits: The properties that are tied to the element property type, like "is it a pointer", "a reference" or "an array", are known as the Positioning properties.
• Numeric Traits: Numeric characteristics are the characteristics which are related to the numeric information concerning the type such as an integer or a floating-point number or its range.
• Container Traits: Container traits are the features that exhibit other traits, e.g. whether they are sequential or associative containers or whether they support operations (insertion, erasure, etc.).
• Iterator Traits: Iterator traits denotes the properties of general iterators, that is, whether they are input/output/forward, and whether they are mutable/constant and so on.

Example:

Let us take an example to illustrate the Traits in C++.

Output:

The type is not a pointer.
The type is a pointer.

Explanation:

• The print_type_information function that acts as a function template and only has one parameter, which is Temp, a template parameter. Inside the function, we use the std: is_pointer<Temp> is the type trait which returns true if Temp is a pointer and false otherwise.
• The std:is_pointer trait, which is a part of the C++ standard library, returns a boolean value at the compile-time, which indicates whether or not the type being pointed to is a pointer. In case the specification is a pointer, the bool type of the trait that we inspect will be true, and false if it is not a pointer.
• In the print_type_information function, the ternary operator is employed to print an output that reveals whether the given type is a pointer or not. The std::cout << (std::is_pointer<Temp>::value ? "a pointer" : "not a pointer" )will print either "a pointer" or "not a pointer" depending on the outcome of the expression std::is_pointer<Temp>::value.
• When print_type_information(x1) is being invoked, the Temp parameter is deduced that Temp is int because x1 is an integer variable. The std::is_pointer<int>::value expression is false, so the function will output "The type is not a pointer".
• When print_type_information(pointer) is invoked, the Temp template parameter is computed as int*, as the pointer is pointing to an integer. The std:is_pointer<int*>::value turning out to be true indicates that the function will print "The type is a pointer".

Conclusion:

Traits being the powerful feature in C++, the programmers can write type-safe, generic, and fast code. By creating feature groups, and exposing behavior and type, you improve software robustness, extensibility, and ease of maintenance. It allows to perform type check at compile time and gives all required information about types. It ensures that C++ code gets written appropriately, and quickly, achieving desired results.