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Marker Traits

How does Rust know to forbid shared access across threads? The answer is in two traits:

• Send: a type T is Send if it is safe to move a T across a thread boundary.
• Sync: a type T is Sync if it is safe to move a &T across a thread boundary.

Send and Sync are unsafe traits. The compiler will automatically derive them for your types as long as they only contain Send and Sync types. You can also implement them manually when you know it is valid.

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• One can think of these traits as markers that the type has certain thread-safety properties.
• They can be used in the generic constraints as normal traits.

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