In some cases, you may need to manually drop a value. When a value is no longer needed, Rust will automatically run a "destructor" on that value. The most common way that a value is no longer needed is when it goes out of scope.
This descructor consists of 2 components:
- A call to
Drop::dropfor that value, if a specialDroptrait is implemented for its type - The automatically generated implementation which recursively calls the destructors of all the fields of a value
Rust automatically calls the destructors of all contained fields, so you don't have to implement Drop in most cases. But there are some cases where it is useful, for example types which directly manage a resource. That resource may be memory, a file descriptor, or something else that must be cleaned up in a special way. Once a value of that type is no longer going to be used, it should "clean up" its resource by freeing the memory or closing the file or socket. This is the job of a destructor, and therefore the job of Drop::drop.
For more information and examples see the official documentation on Drop and std::mem::drop.