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Shortest way to check for null and assign another value if not

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Introduction

Most modern languages provide a null coalescing operator that returns a default value when the expression is null. In C# it is ??, in JavaScript ??, in Python or (with caveats), in Kotlin ?:, and in Swift ??. These operators replace verbose if (x == null) checks with a single concise expression, making null-handling code shorter and more readable.

C# — Null Coalescing Operator (??)

csharp
1// Long form
2string name;
3if (input != null)
4    name = input;
5else
6    name = "default";
7
8// Short form with ??
9string name = input ?? "default";
10
11// Chaining — first non-null wins
12string name = firstName ?? lastName ?? "Anonymous";
13
14// Null coalescing assignment (C# 8+)
15name ??= "default";  // Assigns only if name is null

?? only checks for null. Unlike JavaScript's ||, it does not treat "", 0, or false as needing a default.

JavaScript — Nullish Coalescing (??)

javascript
1// Long form
2let name;
3if (input !== null && input !== undefined) {
4    name = input;
5} else {
6    name = "default";
7}
8
9// Short form with ?? (ES2020)
10let name = input ?? "default";
11
12// ?? vs || — critical difference
13let count = 0;
14console.log(count || 10);   // 10 — || treats 0 as falsy
15console.log(count ?? 10);   // 0  — ?? only checks null/undefined
16
17let text = "";
18console.log(text || "fallback");   // "fallback" — || treats "" as falsy
19console.log(text ?? "fallback");   // ""         — ?? keeps empty string
20
21// Nullish assignment (ES2021)
22let value = null;
23value ??= "default";  // value is now "default"

Python — or Operator (with Caveats)

python
1# Using 'or' — returns first truthy value
2name = input_value or "default"
3
4# CAUTION: 'or' treats all falsy values as needing a default
5count = 0
6result = count or 10  # 10 — wrong if 0 is valid!
7
8text = ""
9result = text or "fallback"  # "fallback" — wrong if "" is valid!
10
11# Safe alternative — explicit None check
12name = input_value if input_value is not None else "default"
13
14# With walrus operator (Python 3.8+)
15# Useful in conditions
16if (value := get_value()) is not None:
17    process(value)

Python has no dedicated null coalescing operator. The or operator works for strings and objects but fails for 0, "", False, and other falsy values.

Kotlin — Elvis Operator (?:)

kotlin
1// Long form
2val name: String = if (input != null) input else "default"
3
4// Short form with ?:
5val name: String = input ?: "default"
6
7// Chaining
8val name = firstName ?: lastName ?: "Anonymous"
9
10// With function calls
11val length = text?.length ?: 0
12
13// Throw on null
14val name = input ?: throw IllegalArgumentException("Name required")
15
16// Return on null
17fun process(input: String?): String {
18    val value = input ?: return "no input"
19    return value.uppercase()
20}

Swift — Nil Coalescing Operator (??)

swift
1// Long form
2let name: String
3if let input = optionalInput {
4    name = input
5} else {
6    name = "default"
7}
8
9// Short form with ??
10let name = optionalInput ?? "default"
11
12// Chaining
13let name = firstName ?? lastName ?? "Anonymous"
14
15// With computed default (lazy evaluation)
16let name = optionalInput ?? expensiveComputation()
17// expensiveComputation() only runs if optionalInput is nil
18
19// Combining with optional chaining
20let count = array?.count ?? 0
21let uppercased = text?.uppercased() ?? "N/A"

PHP — Null Coalescing Operator (??)

php
1// Long form
2$name = isset($input) ? $input : "default";
3
4// Short form with ?? (PHP 7+)
5$name = $input ?? "default";
6
7// Chaining
8$name = $firstName ?? $lastName ?? "Anonymous";
9
10// Null coalescing assignment (PHP 7.4+)
11$name ??= "default";
12
13// Works with arrays and nested access
14$city = $user['address']['city'] ?? "Unknown";
15// No error even if $user or 'address' doesn't exist

Ruby — Conditional Assignment (||=)

ruby
1# Long form
2name = input.nil? ? "default" : input
3
4# Using ||
5name = input || "default"
6
7# Conditional assignment
8name ||= "default"  # Assigns only if name is nil or false
9
10# Ruby 2.3+ safe navigation
11name = user&.name || "Anonymous"

Comparison Table

LanguageOperatorChecks forAssignment form
C#??null??=
JavaScript??null, undefined??=
PythonorAll falsy valuesN/A
Kotlin?:nullN/A
Swift??nilN/A
PHP??null, unset??=
Ruby`\\`nil, false`\\=`

Common Pitfalls

  • Using || instead of ?? in JavaScript: || treats 0, "", false, and NaN as falsy and returns the right-hand side. ?? only triggers on null and undefined. For numeric defaults, count || 10 gives 10 when count is 0, which is usually wrong.
  • Python or treating 0 and "" as needing defaults: value or default returns default when value is 0, "", [], or any falsy value. Use value if value is not None else default for a true null check.
  • Null coalescing with side effects: The right-hand expression is only evaluated if the left is null (lazy evaluation in most languages). But if the right side has side effects (incrementing a counter, making an API call), the behavior depends on whether the left is null — this makes code harder to reason about.
  • Chaining too many operators: a ?? b ?? c ?? d ?? "default" is technically valid but makes it hard to understand the fallback chain. Consider extracting into a function or using a collection-based approach like [a, b, c, d].first { it != null }.
  • Forgetting that ??= does not exist in all languages: Kotlin, Swift, and Python do not have a null coalescing assignment operator. Kotlin uses value = value ?: default and Swift uses if value == nil { value = default }.

Summary

  • C# ??, JavaScript ??, Kotlin ?:, Swift ??, and PHP ?? are null coalescing operators
  • They return the right-hand value only when the left is null (or nil/undefined)
  • JavaScript's ?? differs from || — ?? only checks null/undefined, || checks all falsy values
  • Python's or is not a true null coalescing operator — it treats all falsy values as needing a default
  • Use ??= (C# 8+, JS ES2021, PHP 7.4+) for null coalescing assignment
  • Prefer ?? over || when 0, "", or false are valid values that should not be replaced
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