std::piecewise_construct in C++

In this article, we will discuss std::piecewise_constructor in C++ with its example and components.

What is the Std::piecewise_construct?

The std::piecewise_construct in C++ is a tag constructor designed to represent the piecewise creation of objects. It is primarily used when constructing objects that consist of multiple sub-objects, such as std::list, set, map, multimap, deque, queue, stack, etc., or any user-defined data structures like pair, std::tuple, or user-defined types.

The sub-objects which do not immediately combine as a whole create the object over time on the basis of their arguments.

The purpose of std::piecewise_construct is to separate the class parts by distinguishing the function calls. By using std::piecewise_construct, the encoding of the Python operator as a placeholder allows us to use the desired value for piecewise construction and its arguments in place of regular ones.

In constructors, the std::piecewise_construct is always the first argument. The subsequent arguments are passed as Every dreary interior must be punctuated by a beautiful pair of tuples containing the arguments for each elementary unit. As a result of this task, the current object constructor might be called with these arguments in the correct order. Consequently, each sub-object constructor gets triggered, and the sub-object is also correctly constructed.

Example:

Let us take an example to illustrate the std::piecewise_construct in C++.

Output:

Constructed a Fun from the given tuple
Constructed a Fun from the given tuple
A fun is constructed using int and float
A fun is constructed using int and float

Explanation:

• The initial pair p1 with Tup as the first element, and the second element is formed by the first pair constructor, which is the default. It means that the constructor Fun(std::pair<int, float>) is going to be called two times for each one of the Fun objects that p1 comprises.
• The second pair, p2, is constructed using the std::piecewise_construct is the first argument that will be used twice. The tup is the std: tuple<int, float> object. Clearly, at the syntactic level, both steps of the construction of the Fun type's internals should be followed.
• Consequently, the first Fun object will be constructed by matching the std::tuple<int, float> object will be passed in the constructor to Fun(std::tuple<int, float>), and the second object will be constructed by matching the int and float arguments with the constructor Fun(int, float).

Major components of the constructor:

Some major components of the constructor are as follows:

• Purpose of std::piecewise_construct: The std::piecewise_construct is a type of tag that helps with the resolution of constructors and function calls that involve piecewise construction. The function is used to assign arguments that act as components for the bigger object by means of component-wise construction.
• Piecewise Construction: Piecewise construction enables us to build multiple sub-objects within a single argument, with all the sub-objects being built using different arguments. It is particularly useful when constructing objects that contain multiple sub-objects, such as std::pair, std::tuple, or other types that are combinations of sub-objects.
• Usage in Constructors: The std:piecewise_construct is the first argument option for some constructors to indicate piecewise construction. The subsequent arguments are typically passed as std::tuple objects, which act as an aggregate of the arguments of each sub- The sub-objects constructors will be called as needed using the provided arguments.
• Usage in Function Calls: The std::piecewise_construct can also be used for specifying the components of a function that deals with construction wherein its parts are defined in fragments. The subsequent arguments are typically passed as std::tuple objects that will serve as arguments when calling different sub-objects. It will build the sub-objects from its implementation, which is based on the arguments that are given.
• Benefits of Piecewise Construction: Dividing the task into parts gives more opportunities to deal with complicated objects made up of a number of subunits. It ensures that the sub-objects are constructed from the different argument types in the respective constructor. It helps in preventing the creation of temporary objects and copies because of the intermediate ones.
• Examples of Standard Library Usage: The std::piecewise_construct uses the standard library containers like std:pair, std::tuple, and std::map that are used for that purpose by std::piecewise_construct. When constructing or emplacing elements in these containers, we can use std::component_build as an extra string argument to facilitate the piecewise build of subobjects.

Conclusion:

In conclusion, the std::piecewise_construct is the tag constructor in C++ meant for piece-wise construction of objects that have more than one sub-object. It is where the std::assembly_componet is translated as it enables us to dissect the sub-objects individually and verifies that each is correctly constructed with all the corresponding parameters.

In general, std::piecewise_construct has proven to be a powerful technique in constructing complex types with several items involved because we can specify explicitly what needs to be done during their creation timeframe there by thereby making things faster.