🔗 References & Borrowing in Rust

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📌 What Is a Reference?

A reference lets you borrow a value without taking ownership.

&s1 creates a reference to s1, and the function calculate_length borrows it.

✅ This means the original value isn’t moved, and you can still use it later!

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📏 Immutable References (the default)

By default, references are immutable, meaning you can read the data but not change it.

You can create multiple immutable references at the same time:

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🛠️ Mutable References

If you want to change a borrowed value, you need a mutable reference using &mut:

👉 Rules for mutable references:

• You can have only ONE mutable reference to a piece of data at a time.

❌ This won't work:

Rust enforces this at compile-time to prevent data races.

✅ But you can use a mutable reference after an earlier one is done:

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🚫 Dangling References

Rust does not allow dangling references — that is, references to data that no longer exists:

The value s gets dropped at the end of the function. Returning a reference to it would be dangerous, so Rust prevents this entirely. 🛡️

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🧠 Summary

• &T = immutable reference (read-only)
• &mut T = mutable reference (can modify the value)
• Multiple immutable references are allowed
• Only one mutable reference is allowed at a time
• References let you borrow data without taking ownership
• Rust stops you from using invalid or dangling references at compile time

This is one of Rust’s superpowers: you can write fast, safe code without fear of memory bugs 💥🦀

Next up: Slices – where we dive deeper into referencing parts of data!