Deciding whether to explicitly call return in a function, or rely on implicit returns, is a fundamental consideration in programming, impacting code readability, maintainability, and potential debugging efforts. While some languages encourage or even require explicit returns for clarity, others allow functions to implicitly return the value of the last expression evaluated. Understanding the nuances of each approach, including the specific programming language and coding style guidelines, is crucial for writing robust and understandable code. This blog post will explore the benefits and drawbacks of explicitly calling return in functions, providing practical examples and best practices to help you make informed decisions in your coding endeavors. We’ll delve into how explicit returns affect code clarity, error handling, and overall program efficiency, considering both simple and complex scenarios. The goal is to equip you with the knowledge to consistently write clean, maintainable, and reliable code.

Understanding Explicit vs. Implicit Returns

An explicit return statement clearly indicates the value a function will return to its caller. It uses the return keyword followed by the expression or value to be returned. This approach leaves no ambiguity about the function’s intended output. For example, in JavaScript, an explicit return would look like: function add(a, b) { return a + b; }. The return statement ensures that the sum of a and b is explicitly returned.

In contrast, an implicit return relies on the language’s ability to automatically return the value of the last expression evaluated within the function. This is common in languages like Ruby, Swift (for single-expression closures), and some functional programming languages. For example, in Ruby: def add(a, b) a + b end. Here, the value of a + b is implicitly returned without the need for a return keyword. This can lead to more concise code, but it can also reduce clarity if the function’s logic isn’t immediately obvious.

Choosing between explicit and implicit returns often depends on the specific language, the complexity of the function, and the coding style preferences of the development team. According to a study by Sourcegraph, projects with consistent coding styles tend to have lower bug rates and easier onboarding for new developers. Sourcegraph provides tools that help developers maintain consistency across large codebases.

Benefits of Explicitly Calling Return

One of the primary benefits of explicitly calling return is improved code readability. When a return statement is clearly present, it immediately signals the end of the function’s execution and clarifies the value being returned. This is particularly helpful in longer or more complex functions where the control flow might not be immediately apparent. Explicit returns can also prevent unintended fallthrough, where code execution continues beyond the intended return point, leading to unexpected behavior and difficult-to-debug errors.

Explicit returns can also enhance error handling. By explicitly specifying the return value, you can easily return specific error codes or messages when certain conditions are met. This makes it easier to identify and handle errors gracefully. For example, a function that divides two numbers could explicitly return an error message if the divisor is zero. This clear indication of an error allows the calling code to take appropriate action, such as displaying an error message to the user or logging the error for later investigation.

Furthermore, explicit returns can be crucial for maintaining code consistency within a team. When all developers consistently use explicit returns, it reduces ambiguity and ensures that everyone understands the function’s behavior. This consistency can be enforced through coding style guides and automated linters. Using explicit returns aligns with the principle of least astonishment, making your code easier to understand and maintain for both yourself and others. As Martin Fowler notes in “Refactoring,” readability is a crucial aspect of maintainable code. Refactoring: Improving the Design of Existing Code highlights the importance of clear code for long-term maintainability.

Drawbacks of Implicit Returns

While implicit returns can lead to more concise code, they can also reduce code clarity, especially for developers unfamiliar with the language or the specific coding style. When the return statement is omitted, it may not be immediately obvious what value the function is returning. This can make it harder to understand the function’s behavior and can increase the likelihood of errors. The brevity of implicit returns can be deceptive if it obscures the actual logic.

Implicit returns can also make debugging more challenging. When a function implicitly returns a value, it can be harder to trace the flow of execution and identify the source of errors. This is because the return point is not explicitly marked, making it more difficult to set breakpoints or step through the code in a debugger. In complex functions, this can significantly increase the time and effort required to diagnose and fix bugs. This is especially true if the last expression in a function changes based on complex control flow.

One potential drawback of implicit returns is the reliance on a specific language’s behavior, which might not be universally understood. For instance, if a developer primarily uses languages requiring explicit returns, transitioning to a language with implicit returns could introduce subtle bugs if they aren’t fully aware of how the function’s return value is determined. Therefore, understanding the language’s nuances is paramount. Good documentation and consistent coding practices can mitigate these risks.

Best Practices and Examples

To illustrate the best practices, consider a JavaScript function that calculates the area of a rectangle. An explicit return would look like this:

javascript function calculateArea(width, height) { if (width <= 0 || height <= 0) { return “Invalid dimensions”; } const area = width height; return area; } This example clearly shows the error handling and the calculated area being returned. Now, consider the same function with an implicit return (although JavaScript generally favors explicit returns for clarity):

javascript function calculateArea(width, height) { if (width <= 0 || height <= 0) { return “Invalid dimensions”; } width height; // Implicit return (not recommended in JavaScript) } While syntactically valid (in some languages), the second example is less clear. For enhanced clarity and maintainability, always use explicit returns in JavaScript, especially in functions with multiple code paths or error handling. When working in teams, enforce a consistent coding style that favors explicit returns to minimize ambiguity and ensure that everyone understands the function’s behavior.

Featured Snippet: One crucial guideline is to always consider the context and complexity of the function. For simple, single-expression functions, an implicit return might be acceptable if it improves readability without sacrificing clarity. However, for more complex functions with multiple code paths, error handling, or side effects, an explicit return is almost always the better choice. This practice ensures that the function’s behavior is clear and predictable, reducing the likelihood of errors and improving maintainability.

FAQ Section

Q: When should I use explicit returns?

A: Use explicit returns in complex functions, when error handling is involved, or when working in a team to maintain consistency.

Q: What are the benefits of implicit returns?

A: Implicit returns can lead to more concise code, especially in simple functions, but they should be used judiciously.

Q: Are implicit returns always a bad practice?

A: No, implicit returns are not always bad. In some languages and specific contexts (e.g., single-expression lambda functions), they can improve readability. However, they should be used with caution.

1. Steps to Choose Between Explicit and Implicit Returns:
2. Assess the complexity of the function.
3. Consider the coding style guidelines of your team or project.
4. Evaluate the potential for ambiguity and error.
5. Prioritize readability and maintainability.

Ultimately, the decision of whether to explicitly call return in a function hinges on a balance between code conciseness and clarity. Prioritizing readability, especially in larger projects or collaborative environments, often makes explicit returns the superior choice. By ensuring that the return path is clearly defined, you reduce the potential for misunderstandings and make your code easier to maintain and debug. Consider exploring more advanced functional programming concepts to further refine your understanding of function design. You can also read the Google Style Guide for more coding conventions. Continue practicing both explicit and implicit return styles to develop a feel for when each is most appropriate, and don’t hesitate to experiment and refactor your code to find the best balance for your specific needs. Happy coding!

Question & Answer :
A while back I got rebuked by Simon Urbanek from the R core team (I believe) for recommending a user to explicitly calling return at the end of a function (his comment was deleted though):

foo = function() { return(value) } 

instead he recommended:

foo = function() { value } 

Probably in a situation like this it is required:

foo = function() { if(a) { return(a) } else { return(b) } } 

His comment shed some light on why not calling return unless strictly needed is a good thing, but this was deleted.

My question is: Why is not calling return faster or better, and thus preferable?

Question was: Why is not (explicitly) calling return faster or better, and thus preferable?

There is no statement in R documentation making such an assumption.
The main page ?‘function’ says:

function( arglist ) expr return(value) 

Is it faster without calling return?

Both function() and return() are primitive functions and the function() itself returns last evaluated value even without including return() function.

Calling return() as .Primitive('return') with that last value as an argument will do the same job but needs one call more. So that this (often) unnecessary .Primitive('return') call can draw additional resources. Simple measurement however shows that the resulting difference is very small and thus can not be the reason for not using explicit return. The following plot is created from data selected this way:

bench_nor2 <- function(x,repeats) { system.time(rep( # without explicit return (function(x) vector(length=x,mode="numeric"))(x) ,repeats)) } bench_ret2 <- function(x,repeats) { system.time(rep( # with explicit return (function(x) return(vector(length=x,mode="numeric")))(x) ,repeats)) } maxlen <- 1000 reps <- 10000 along <- seq(from=1,to=maxlen,by=5) ret <- sapply(along,FUN=bench_ret2,repeats=reps) nor <- sapply(along,FUN=bench_nor2,repeats=reps) res <- data.frame(N=along,ELAPSED_RET=ret["elapsed",],ELAPSED_NOR=nor["elapsed",]) # res object is then visualized # R version 2.15 

The picture above may slightly difffer on your platform. Based on measured data, the size of returned object is not causing any difference, the number of repeats (even if scaled up) makes just a very small difference, which in real word with real data and real algorithm could not be counted or make your script run faster.

Is it better without calling return?

Return is good tool for clearly designing “leaves” of code where the routine should end, jump out of the function and return value.

# here without calling .Primitive('return') > (function() {10;20;30;40})() [1] 40 # here with .Primitive('return') > (function() {10;20;30;40;return(40)})() [1] 40 # here return terminates flow > (function() {10;20;return();30;40})() NULL > (function() {10;20;return(25);30;40})() [1] 25 > 

It depends on strategy and programming style of the programmer what style he use, he can use no return() as it is not required.

R core programmers uses both approaches ie. with and without explicit return() as it is possible to find in sources of ‘base’ functions.

Many times only return() is used (no argument) returning NULL in cases to conditially stop the function.

It is not clear if it is better or not as standard user or analyst using R can not see the real difference.

My opinion is that the question should be: Is there any danger in using explicit return coming from R implementation?

Or, maybe better, user writing function code should always ask: What is the effect in not using explicit return (or placing object to be returned as last leaf of code branch) in the function code?