如果我为结构编写自定义放置实现，是否需要指定“放置（项目）”？ Rust

Question

I'm working with OpenGL in rust currently.

and i want to create objects like VAOs and Textures into structs

now, i wrote a custom drop implementation that calls something like glDeleteTexture when the objects lifetime is finished so that it clears up the memory in VRAM.

Will the actual data of the object still remain in the RAM if i dont specifically call drop(struct_attribute) for all the attributes

I'm expecting for rust to automatically call drop on every attribute but i just wanna make sure so that i dont waste my time or memory if im wrong.

Answer 1

You do not need to manually drop other members when you implement drop, nor would you be able to.

Take for example:

struct A {
    handle: i32,
    a: String,
    // ...
}

impl Drop for A {
    fn drop(&mut self) {
        // Do something with `handle`
        // ...

        // `a` will be dropped *after* this function returns automatically
    }
}

Drop::drop receives a &mut self , which makes it so you cannot (without unsafe or replacing the original value) drop self.a . If you did somehow drop it, rust would then proceed to drop it again after drop returns, causing a double free.

Drop doesn't serve for dropping a type, despite it's name. It's more akin to a finalizer that runs code right before the type is dropped.

Answer 2

drop is simply defined as fn drop<T>(_: T) {} , it does absolutely nothing special. Rust automatically picks up everything for you: almost every value is dropped by Rust (some exceptions include when the program diverges, but don't worry about it).