In tidylab/R6P: Design Patterns in R

source(file.path(usethis::proj_get(), "vignettes", "_common.R"))

Singleton ensures a class only has one instance, and provide a global point of access to it.

How It Works

1. Create only one instance of the Singleton class; and
2. If an instance exists, then serve the same object again.

The main features of Singleton are:

• Ensuring that one and only one object of the class gets created;

• Providing an access point for an object that is global to the program; and

• Controlling concurrent access to resources that are shared.

When to Use It

• In situations that require exactly one instance of a class, that must be accessible to clients from a well-known access point. See the Counter example.

stop("Singletons can be a problem in multi-threaded applications, especially when they manipulate mutable data.")

message("Singletons work well for immutable data, such as reading from some data source, since anything that can’t change isn’t going to run into thread clash problems.")

tidylab/R6P documentation built on Dec. 23, 2024, 9:22 a.m.