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58 lines
2.0 KiB
58 lines
2.0 KiB
3 years ago
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# `PhantomDrop`
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Small library for `defer`ing the running of function until the end of a block.
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# Usage
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It is similar to `marker` types, useful for adding destructors into structs that you don't want to implement `Drop` on themselves, and also for deferring function calls.
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## Extra destructors
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To add a destructor into a struct without needing to implement `Drop` on the struct itself (which can have some of its own issues, such as losing the ability for partial moves), we can use `PhantomDrop` as a field in the structure.
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Note that when doing this, since closure types are opaque, the field may need to be sized.
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## Deferring
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Similar to the `defer` mechanism in Go, we can use this to defer the calling of functions
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```rust
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fn do_something()
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{
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let _guard = phantomdrop::defer(|| println!("Hello!"));
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// do some work
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} // "Hello!" will now be printed when the function returns or unwinds (unless unwinds are disabled).
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```
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# Holding data
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The guard can also hold a value
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```rust
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fn do_something(print: String)
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{
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let _guard = PhantomDrop::new(print, |string| println!("Dropped: {}", string));
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// do some work
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} // `print` will now be printed here.
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```
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## Capturing
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We can also capture a value, by reference, mutable reference, or moving.
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Both holding a value within the guard and a capturing closure can be used at the same time.
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```rust
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fn do_something(print: String)
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{
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let _guard = phantomdrop::defer(move || println!("Dropped: {}", print)); // Moves `print` into itself.
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// do some work
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} // `print` will now be printed here.
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fn do_something_by_reference(print: String)
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{
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let _guard = phantomdrop::defer(|| println!("Dropped: {}", print)); // Holds an immutable reference to `print`.
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let trimmed = print.trim(); // Can still be used
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} // `print` will now be printed here.
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fn do_something_by_mutable_reference(print: &mut String)
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{
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let _guard = phantomdrop::defer(|| *print = String::from("Dropped")); // Holds a mutable reference to `print`.
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} // `print` will now be set to "Dropped" here.
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```
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# License
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GPL'd with <3
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