feat: Add solution for exercise 13_variadic (#22)

[thearpankumar]

This PR implements the solution for exercise 13_variadic, which teaches variadic functions in Go.

The Sum function accepts any number of integers using the ...int syntax and returns their total sum by iterating through the arguments with a for-range loop.

Implementation Details

• Created internal/exercises/solutions/13_variadic/variadic.go with a simple, idiomatic implementation
• The solution iterates through variadic integers and accumulates the sum
• Code follows Go best practices: clear variable names, simple logic

Testing

• ✅ Solution passes all tests: ./bin/golearn verify 13_variadic --solution
• ✅ Template still fails as expected (ensures incomplete code for student learning)
• ✅ Code is properly formatted with gofmt
• ✅ Passes go vet checks

Checklist

• Tests pass: make verify or golearn verify 13_variadic --solution
• Docs updated (README/CONTRIBUTING) if needed (no updates needed)
• No large new dependencies (no new dependencies added)

Output

$ ./bin/golearn verify 13_variadic --solution
==> 13_variadic: Variadic Functions (solution)
PASSED 13_variadic (solution)

Related issues

Fixes #22

The branch solution/13_variadic-issue-22 is already pushed to the remote repository.

Summary by CodeRabbit

• New Features
  • Introduced a variadic sum utility that lets you add any number of integers in one call. Useful for aggregations, totals, and quick calculations without manual loops. Provides a straightforward way to compute totals across dynamic inputs, improving readability and reducing boilerplate in examples and apps.

[coderabbitai]

Walkthrough

Introduces a new Go package with a variadic sum function. The function accepts a variable number of integers, iterates through them, accumulates a total, and returns the result.

Changes

Cohort / File(s)	Summary of Changes
Variadic sum utility internal/exercises/solutions/13_variadic/variadic.go	Added package variadic with exported function Sum(nums ...int) int that iterates over inputs and returns their sum.

Sequence Diagram(s)

sequenceDiagram
    actor Caller
    participant Variadic as variadic.Sum
    Caller->>Variadic: Sum(nums...int)
    note over Variadic: Initialize total = 0<br/>Loop over nums<br/>Accumulate total
    Variadic-->>Caller: int (total)

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Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Poem

I hop through code with ears held high,
Counting carrots passing by—
One, two, many, gathered neat,
A variadic, crunchy treat.
Sum them up, then quickly run—
Totals tallied, job well done! 🥕✨

Pre-merge checks and finishing touches

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title Check	✅ Passed	The title succinctly indicates the addition of the solution for exercise 13_variadic and follows a conventional commit prefix. It references the related issue number for context without including extraneous detail. The phrasing is concise and directly communicates the PR’s main objective.
Linked Issues Check	✅ Passed	The PR implements the Sum function for exercise 13_variadic in the designated solutions directory and successfully verifies it passes all tests. It cross‐references issue #22 in the description and maintains idiomatic Go formatting and vet compliance. This meets the linked issue’s requirements for code implementation, test passing, and issue linking.
Out of Scope Changes Check	✅ Passed	All changes in this PR are confined to adding a single solution file under internal/exercises/solutions/13_variadic and there are no modifications to unrelated modules or directories. The exercise template remains untouched to preserve the learning experience. Therefore, there are no out-of-scope changes.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

✨ Finishing touches

• 📝 Generate Docstrings

🧪 Generate unit tests

• Create PR with unit tests
• Post copyable unit tests in a comment

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📜 Recent review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between e5420af and 07340a4.

📒 Files selected for processing (1)

• internal/exercises/solutions/13_variadic/variadic.go (1 hunks)

🔇 Additional comments (1)

internal/exercises/solutions/13_variadic/variadic.go (1)

1-10: LGTM! Clean and idiomatic variadic function implementation.

The Sum function correctly demonstrates Go's variadic parameter syntax and provides a clear, minimal implementation. The logic handles the empty-arguments case correctly (returns 0), and the code follows Go conventions.

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