What is the difference in Swift between 'unowned(safe)' and 'unowned(unsafe)'?

Question

Apple\'s Swift Programming Language Guide mentions the capture specifiers unowned(safe) and unowned(unsafe), in addition to weak

Answer 1

Variable is accessed when it was dellocated already with attribute:

unowned

• Program knows it is invalid, and goes crash immediately.
• Behavior is defined.

unowned(unsafe)

• Program knows nothing.
• It may crash immediately.
• It may access unknown memory address and have strange state until it it dies at surprise location.
• Behavior is undefined. Life gets harder.