eval(substitute()) within a R6 object

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Summary

The issue at hand is using eval(substitute()) within an R6 object to evaluate an expression. The problem arises when trying to use basic operators like ==, +, etc., which are not defined within the object’s environment. This leads to errors, as seen in the example provided.

Root Cause

The root cause of this issue is that the R6 object does not inherit the base environment of R, where these basic operators are defined. Instead, it has its own environment, which only includes the methods and fields defined within the class. The causes of this issue include:

  • The R6 object having its own isolated environment
  • The eval() function only looking for functions and variables within the specified environment
  • Basic operators not being defined within the R6 object by default

Why This Happens in Real Systems

This issue occurs in real systems because R6 objects are designed to be self-contained and encapsulated, which means they do not automatically inherit the entire R environment. This is a trade-off between encapsulation and convenience. While it provides better organization and structure to the code, it also requires more explicit definitions of methods and operators.

Real-World Impact

The real-world impact of this issue includes:

  • Increased code complexity: Having to define basic operators explicitly can lead to more complex and verbose code
  • Error-prone code: Forgetting to define an operator or function can lead to errors that are difficult to track down
  • Limited flexibility: The need to explicitly define operators can limit the flexibility of the code and make it harder to adapt to changing requirements

Example or Code

A <- R6::R6Class('A', public=list(
  f1 = 1,
  `==` = function(x, y) x == y,
  `+` = function(x, y) x + y
))
test <- A$new()
eval(substitute(f1 == 1), test)
eval(substitute(f1 + 1), test)

How Senior Engineers Fix It

Senior engineers can fix this issue by using the env argument of the eval() function to specify the environment in which to evaluate the expression. This can include the baseenv(), which contains all the basic operators and functions. Alternatively, they can define the necessary operators and functions within the R6 object itself.

Why Juniors Miss It

Juniors may miss this issue because they:

  • Are not familiar with the R6 object model and its implications
  • Do not understand the scope and environment of the eval() function
  • Are not aware of the need to explicitly define operators and functions within the R6 object
  • Do not consider the trade-offs between encapsulation and convenience when designing their code. Key takeaways include understanding the R6 object model, the eval() function, and the importance of explicit definitions.

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