使用泛型函数制作盒装特征会返回错误

Question

I'm trying to abstract reading and writing memory from a process in my Rust program. Here is some example code describing the issue:

trait ProcessHandle {
    // Create a new process handle from pid
    fn new(pid: u32) -> Box<dyn ProcessHandle>;
    // Read value from process of type T from the process
    // (type T has an implicit Sized trait so we know how
    // large the value that we're reading is)
    fn read_memory<T>(&self, address: u64) -> T;
    // Write value of type T to process
    fn write_memory<T>(&self, address: u64, value: T);
}

struct ExampleProcessHandle {
    pid: u32
}

impl ProcessHandle for ExampleProcessHandle {
    fn new(pid: u32) -> Box<dyn ProcessHandle> {
        Box::new(Self{pid})
    }

    fn read_memory<T>(&self, address: u64) -> T {
        // read memory from process at `address`
        unsafe { std::mem::zeroed::<T>() }
    }

    fn write_memory<T>(&self, address: u64, value: T) {
        // write to process
        return
    }
}

fn main() {
    let handle = ExampleProcessHandle::new(10);
    // Should print 0
    println!("{:x}", handle.read_memory::<u32>(0x111111));
}

When compiling, I get the following error:

the trait `ProcessHandle` cannot be made into an object

Is there any way I can have generic functions in a trait without making every struct I use it in generic?

Answer 1

You cannot make a trait object out of ProcessHandle because it's not safe , quoting from the book:

A trait is object safe if all the methods defined in the trait have the following > properties:

1. The return type isn't Self .
2. There are no generic type parameters.

Your write_memory method has generic type parameters

Answer 2

I found a workaround by creating non generic functions in my ProcessHandle trait and adding the generic functions using impl ProcessHandle