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Unsafe keyword shifts responsibility

	Is Memory Safe?	Responsibility for Memory Safety
Safe Rust	Yes	Compiler
Unsafe Rust	Yes	Programmer

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Who has responsibility for memory safety?

• Safe Rust → compiler
• Unsafe Rust → programmer

“While writing safe Rust, you cannot create memory safety problems. The compiler will ensure that a program with mistakes will not build.”

“The unsafe keyword shifts responsibility for maintaining memory safety from the compiler to programmers. It signals that there are preconditions that must be satisfied.

“To uphold that responsibility, programmers must ensure that they've understood what the preconditions are and that their code will always satisfy them.

“Throughout this course, we'll use the term safety preconditions to describe this situation.”

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