Yoda conditions

Last updated

In programming jargon, Yoda conditions (also called Yoda notation) is a programming style where the two parts of an expression are reversed from the typical order in a conditional statement. A Yoda condition places the constant portion of the expression on the left side of the conditional statement.

Contents

Yoda conditions are part of the coding standards for Symfony [1] and WordPress. [2]

Origin

The name for this programming style is derived from the Star Wars character Yoda, who speaks English with a non-standard syntax [3] (e.g., "When 900 years old you reach, look as good you will not." [4] [5] ). Thomas M. Tuerke claims to have coined the term Yoda notation and first published it online in 2006. [6] According to him, the term Yoda condition was later popularized by Félix Cloutier in 2010.

Example

Usually a conditional statement would be written as:

if($value==42){/* ... */}// Reads like: "If the value equals 42..."

Yoda conditions describe the same expression, but reversed:

if(42==$value){/* ... */}// Reads like: "If 42 equals the value..."

Advantage

Readability of logically-chained comparisons

Some languages, such as Python, support "chained" comparison operators ("comparators") in their syntax. [7] Thus, the following lines are logically equivalent:

# Using chained comparators:if3.14<y<=42:...# Logically equivalent to:if(3.14<y)and(y<=42):...

Notice that the second form naturally uses Yoda syntax in the left-hand comparison (3.14 < y). Consider the same line without Yoda syntax:

if(y>3.14)and(y<=42):...

When handwriting math, many authors prefer the "chained" notation (example, example). When programming in a language that does not literally support the chained notation, the author may prefer the Yoda syntax, as it at least visually evokes the familiar chained notation.

Detecting programmer mistakes

For symmetric comparisons, such as equality, swapping the left and right operands does not change the behavior of the program. In programming languages that use a single equals sign (=) for assignment expressions, one might mistakenly write an assignment expression where an equality comparison was intended.

if(myNumber=42){/* ... */}// This assigns 42 to myNumber instead of evaluating the desired condition

Using Yoda conditions:

if(42=myNumber){/* ... */}// An error this is and compile it will not

Since literal expressions such as 42 are not assignable (they are not "lvalues"), assignment-equality confusion in Yoda conditions often manifests as a compile-time semantic error.

BooleanmyBoolean=null;if(myBoolean==true){/* ... */}// This causes a NullPointerException in Java Runtime, but legal in compilation.// This happens because Java will try to call myBoolean.booleanValue() on a null Object.

Changing the target of dynamic dispatch

In most object-oriented programming languages, the receiver of a method call is written to the left of the call's other arguments. At the same time, in non-Yoda comparisons, the variable that is the subject of comparison is written on the left-hand side. Comparison method calls are thus ordinarily dynamically dispatched on the object being compared, which is not always desirable.

StringmyString=null;if(myString.equals("foobar")){/* ... */}// This causes a NullPointerException in Java

With Yoda conditions, the call can be dispatched on a constant object instead.

StringmyString=null;if("foobar".equals(myString)){/* ... */}// This resolves to false without throwing a NullPointerException

Criticism

Yoda conditions are criticized for compromising readability by increasing the cognitive load of reading the code. [8] [9] [10]

Some programming languages (such as Swift, Kotlin and versions of Python below 3.8) do not allow variable assignments within conditionals—for example by requiring that assignments do not return a value, or by defining as part of their grammar the invariant that conditions cannot contain assignment statements—in which case this error is impossible to encounter (that is, it would be detected as a syntax error by the parser prior to a program ever being allowed to enter into runtime). [11] Many compilers produce a warning for code such as if (myNumber = 42) (e.g., the GCC -Wall option warns suggest parentheses around assignment used as truth value), which alerts the programmer to the likely mistake. In dynamic languages like JavaScript, linters such as ESLint can warn on assignment inside a conditional. [12] Python 3.8 introduced assignment expressions, but uses the walrus operator := instead of a regular equal sign (=) to avoid bugs which simply confuse == with =. [13]

Another disadvantage appears in C++ when comparing non-basic types as the == is an operator and there may not be a suitable overloaded operator function defined. Example: a Microsoft's CComBSTR compare against a string literal, written as if (L"Hello" == cbstrMessage), does not map to an overload function. [14]

Related Research Articles

Icon is a very high-level programming language based on the concept of "goal-directed execution" in which code returns a "success" along with valid values, or a "failure", indicating that there is no valid data to return. The success and failure of a given block of code is used to direct further processing, whereas conventional languages would typically use boolean logic written by the programmer to achieve the same ends. Because the logic for basic control structures is often implicit in Icon, common tasks can be completed with less explicit code.

In computer programming, an assignment statement sets and/or re-sets the value stored in the storage location(s) denoted by a variable name; in other words, it copies a value into the variable. In most imperative programming languages, the assignment statement is a fundamental construct.

<span class="mw-page-title-main">Conditional (computer programming)</span> Control flow statement that executes code according to some condition(s)

In computer science, conditionals are programming language constructs that perform different computations or actions or return different values depending on the value of a Boolean expression, called a condition.

In computer science, type conversion, type casting, type coercion, and type juggling are different ways of changing an expression from one data type to another. An example would be the conversion of an integer value into a floating point value or its textual representation as a string, and vice versa. Type conversions can take advantage of certain features of type hierarchies or data representations. Two important aspects of a type conversion are whether it happens implicitly (automatically) or explicitly, and whether the underlying data representation is converted from one representation into another, or a given representation is merely reinterpreted as the representation of another data type. In general, both primitive and compound data types can be converted.

This is a list of operators in the C and C++ programming languages. All the operators listed exist in C++; the column "Included in C", states whether an operator is also present in C. Note that C does not support operator overloading.

In computer programming, the ternary conditional operator is a ternary operator that is part of the syntax for basic conditional expressions in several programming languages. It is commonly referred to as the conditional operator, conditional expression, ternary if, or inline if. An expression if a then b else c or a ? b : c evaluates to b if the value of a is true, and otherwise to c. One can read it aloud as "if a then b otherwise c". The form a ? b : c is the most common, but alternative syntax do exist; for example, Raku uses the syntax a ?? b !! c to avoid confusion with the infix operators ? and !, whereas in Visual Basic .NET, it instead takes the form If(a, b, c).

Short-circuit evaluation, minimal evaluation, or McCarthy evaluation is the semantics of some Boolean operators in some programming languages in which the second argument is executed or evaluated only if the first argument does not suffice to determine the value of the expression: when the first argument of the AND function evaluates to false, the overall value must be false; and when the first argument of the OR function evaluates to true, the overall value must be true.

In computer programming, operators are constructs defined within programming languages which behave generally like functions, but which differ syntactically or semantically.

<span class="mw-page-title-main">Boolean data type</span> Data having only values "true" or "false"

In computer science, the Boolean is a data type that has one of two possible values which is intended to represent the two truth values of logic and Boolean algebra. It is named after George Boole, who first defined an algebraic system of logic in the mid 19th century. The Boolean data type is primarily associated with conditional statements, which allow different actions by changing control flow depending on whether a programmer-specified Boolean condition evaluates to true or false. It is a special case of a more general logical data type—logic does not always need to be Boolean.

In computer science, a relational operator is a programming language construct or operator that tests or defines some kind of relation between two entities. These include numerical equality and inequalities.

In programming, a gotcha is a valid construct in a system, program or programming language that works as documented but is counter-intuitive and almost invites mistakes because it is both easy to invoke and unexpected or unreasonable in its outcome.

<span class="mw-page-title-main">JavaScript syntax</span> Set of rules defining correctly structured programs

The syntax of JavaScript is the set of rules that define a correctly structured JavaScript program.

<span class="mw-page-title-main">Python syntax and semantics</span> Set of rules defining correctly structured programs

The syntax of the Python programming language is the set of rules that defines how a Python program will be written and interpreted. The Python language has many similarities to Perl, C, and Java. However, there are some definite differences between the languages. It supports multiple programming paradigms, including structured, object-oriented programming, and functional programming, and boasts a dynamic type system and automatic memory management.

The conditional operator is supported in many programming languages. This term usually refers to ?: as in C, C++, C#, and JavaScript. However, in Java, this term can also refer to && and ||.

In computer science, a three-way comparison takes two values A and B belonging to a type with a total order and determines whether A < B, A = B, or A > B in a single operation, in accordance with the mathematical law of trichotomy.

The null coalescing operator is a binary operator that is part of the syntax for a basic conditional expression in several programming languages, such as : C# since version 2.0, Dart since version 1.12.0, PHP since version 7.0.0, Perl since version 5.10 as logical defined-or, PowerShell since 7.0.0, and Swift as nil-coalescing operator.

The syntax and semantics of PHP, a programming language, form a set of rules that define how a PHP program can be written and interpreted.

XPath is an expression language designed to support the query or transformation of XML documents. It was defined by the World Wide Web Consortium (W3C) in 1999, and can be used to compute values from the content of an XML document. Support for XPath exists in applications that support XML, such as web browsers, and many programming languages.

In certain computer programming languages, the Elvis operator, often written ?:, is a binary operator that returns the evaluated first operand if that operand evaluates to a value likened to logically true, and otherwise returns the evaluated second operand. This is identical to a short-circuit or with "last value" semantics. The notation of the Elvis operator was inspired by the ternary conditional operator, ? :, since the Elvis operator expression A ?: B is approximately equivalent to the ternary conditional expression A ? A : B.

In object-oriented programming, the safe navigation operator is a binary operator that returns null if its first argument is null; otherwise it performs a dereferencing operation as specified by the second argument.

References

  1. ↑ "Coding Standards (Contributing to Symfony)". Symfony.com. Retrieved 12 November 2016.
  2. ↑ "PHP Coding Standards | Coding Standards Handbook". WordPress Developer Resources. Retrieved 25 July 2021.
  3. ↑ Pullum, Geoffrey K. (18 May 2005). "Yoda's Syntax the Tribune Analyzes; Supply More Details I Will!". Itre.cis.upenn.edu. Language Log. Retrieved 22 December 2014. One way to look at Yoda's syntax is that it shows signs of favoring OSV syntax (Object-Subject-Verb) as the basic order in the simple clause.
  4. ↑ "The StarWars.com 10: Best Yoda Quotes". starwars.com. Lucasfilm, Ltd. 26 November 2013. Retrieved 22 December 2014. When nine hundred years old you reach, look as good you will not.
  5. ↑ "Quotes for Yoda (Character)". imdb.com. Amazon. Retrieved 22 December 2014. When nine hundred years old *you* reach, look as good *you* will not, hmm?
  6. ↑ "Yoda Notation (aka Yoda Condition)—Origin of the term". 17 April 2013. Retrieved 26 December 2020.
  7. ↑ "Comparisons". Python Library Reference. Python Software Foundation. 2008.
  8. ↑ Paris, Grégoire (24 January 2020). "Why using Yoda conditions you should probably not be". DEV Community. Retrieved 30 January 2022.
  9. ↑ Classic, Mike (16 August 2017). "Yoda Conditions: Why You Shouldn't Use Them". mikeclassic.ca. Retrieved 30 January 2022.
  10. ↑ Contieri, Maxi (7 February 2023). "Code Smell 195 - Yoda Conditions". Maximiliano Contieri - Software Design. Retrieved 22 May 2024.
  11. ↑ "Basic Operators — The Swift Programming Language (Swift 5.6)". docs.swift.org. Apple. Retrieved 30 January 2022.
  12. ↑ "disallow assignment operators in conditional statements". eslint.org. Retrieved 29 January 2022.
  13. ↑ Angelico, Chris; Peters, Tim; van Rossum, Guido (28 February 2018). "PEP 572 -- Assignment Expressions". Python.org. Retrieved 18 July 2021.
  14. ↑ "CComBSTR Class". docs.microsoft.com. Microsoft. 3 August 2021. Retrieved 30 January 2022.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.