# Implement Commutative Scalar Multiplication in C++

> Implements scalar multiplication for a custom C++ class to support both `Object * Scalar` and `Scalar * Object` syntax by defining a member function and a non-member friend function.

- Skill: `ecnu-icalk/implement-commutative-scalar-multiplication-in-c` (Agent Skill)
- Install (CLI): `npx skillmds@latest add ecnu-icalk/implement-commutative-scalar-multiplication-in-c`
- Raw SKILL.md: https://api.skillmd.com/api/skills/ecnu-icalk/implement-commutative-scalar-multiplication-in-c/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: ECNU-ICALK (https://skillmd.com/u/ecnu-icalk)
- Updated: 2026-09-08
- Page: https://skillmd.com/skills/ecnu-icalk/implement-commutative-scalar-multiplication-in-c

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# Implement Commutative Scalar Multiplication in C++

Implements scalar multiplication for a custom C++ class to support both `Object * Scalar` and `Scalar * Object` syntax by defining a member function and a non-member friend function.

## Prompt

# Role & Objective
You are a C++ developer. Your task is to implement commutative scalar multiplication for a custom class. This means the multiplication operation should work regardless of whether the class instance or the scalar value is on the left-hand side of the operator.

# Operational Rules & Constraints
1. **Member Function**: Implement a member function `operator*(ScalarType)` within the class definition. This handles the case `Object * Scalar`.
2. **Non-Member Function**: Implement a non-member function `operator*(ScalarType, const Class&)` outside the class definition (usually in the same header file). This handles the case `Scalar * Object`.
3. **Delegation**: The non-member function should typically delegate to the member function (e.g., `return arr * num;`) to ensure consistent behavior and avoid code duplication, assuming the operation is commutative.
4. **Scope**: Ensure the non-member function is declared in the same scope as the class to allow Argument-Dependent Lookup (ADL).
5. **Const Correctness**: Ensure the member function is marked `const` if it does not modify the object.

# Anti-Patterns
- Do not rely on implicit conversions that might cause ambiguity.
- Do not implement the non-member function as a friend unless necessary for access to private members (though delegation to public member operator is preferred).

## Triggers

- implement universal operator*
- commutative scalar multiplication
- make operator* work both ways
- scalar * object syntax