Variadic Templates and Fold Expressions in Modern C++

Advanced13 min read•Updated: 2026-10-22

🪄 Variadic Templates and Fold Expressions

Introduction

A variadic template accepts an arbitrary number of arguments of arbitrary types using parameter packs (typename... Args). C++17 introduced fold expressions, transforming complex recursive parameter-pack expansions into simple one-line statements.

🤹 Modern C++17 Fold Expressions

1#include <iostream>
2#include <string>
3 
4// 1. Unary Left Fold: (... + args) evaluates: (((a + b) + c) + d)
5template <typename... Args>
6auto sumAll(Args... args) {
7    return (... + args);
8}
9 
10// 2. Comma Fold Expression: Printing arbitrary items separated by space
11template <typename... Args>
12void printLine(const Args&... args) {
13    // Expands: (std::cout << arg1 << ' ', std::cout << arg2 << ' ', ...)
14    ((std::cout << args << " "), ...) << "\n";
15}
16 
17int main() {
18    std::cout << "Sum (1+2+3+4+5): " << sumAll(1, 2, 3, 4, 5) << "\n";
19    std::cout << "Float Sum:       " << sumAll(1.5, 2.5, 3.5) << "\n";
20 
21    printLine("Welcome", "to", "MSK", "Institute", 2026, "Batch");
22    return 0;
23}

💡 Types of Fold Expressions

Unary Right Fold: (args op ...)
Unary Left Fold: (... op args)
Binary Right Fold: (args op ... op init)
Binary Left Fold: (init op ... op args)

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Type Traits (<type_traits>), std::enable_if, and SFINAE

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Template Specialization (Full and Partial Specialization)	Type Traits (<type_traits>), std::enable_if, and SFINAE

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Type Traits (<type_traits>), std::enable_if, and SFINAE

Variadic Templates and Fold Expressions in Modern C++

Advanced13 min read•Updated: 2026-10-22

Study Materials

🪄 Variadic Templates and Fold Expressions

Introduction

🤹 Modern C++17 Fold Expressions

1#include <iostream>
2#include <string>
3 
4// 1. Unary Left Fold: (... + args) evaluates: (((a + b) + c) + d)
5template <typename... Args>
6auto sumAll(Args... args) {
7    return (... + args);
8}
9 
10// 2. Comma Fold Expression: Printing arbitrary items separated by space
11template <typename... Args>
12void printLine(const Args&... args) {
13    // Expands: (std::cout << arg1 << ' ', std::cout << arg2 << ' ', ...)
14    ((std::cout << args << " "), ...) << "\n";
15}
16 
17int main() {
18    std::cout << "Sum (1+2+3+4+5): " << sumAll(1, 2, 3, 4, 5) << "\n";
19    std::cout << "Float Sum:       " << sumAll(1.5, 2.5, 3.5) << "\n";
20 
21    printLine("Welcome", "to", "MSK", "Institute", 2026, "Batch");
22    return 0;
23}

💡 Types of Fold Expressions

Unary Right Fold: (args op ...)
Unary Left Fold: (... op args)
Binary Right Fold: (args op ... op init)
Binary Left Fold: (init op ... op args)

Next Lesson

Type Traits (<type_traits>), std::enable_if, and SFINAE

Continue learning with hands-on practice, examples, and exercises in the upcoming topic.

Related Lessons

Previous Lesson	Next Lesson
Template Specialization (Full and Partial Specialization)	Type Traits (<type_traits>), std::enable_if, and SFINAE

Practice Quiz

Test your understanding of this lesson with 1 questions. Each question has one correct answer.

Previous Next