How to improve this snippet of code to get compile success?

help
1

I want to implement a function that return process::stdout value, I take Output as parameter

fn get_stdout(output: &Output) -> String {
    return (String::from_utf8(output.stdout)).unwrap();
// error in `output.stdout` 
}

cannot move out of output.stdout which is behind a shared reference
move occurs because output.stdout has type Vec<u8>, which does not implement the Copy trait

2

You take not Output, but &Output - that's the important distinction, since you can't steal the data from behind the reference. If you intend to reuse Output after call to get_stdout, you have to clone the standard output data, i.e. use String::from_utf8(output.stdout.clone()); otherwise, just change the argument to be Output directly.

3

I don't understand that I have used a borrowed Output, I should be granted to access all methods/properties, why still need to clone

4

You can access properties, but you can't move out of them. The Vec<u8> stored in output.stdout must remain unchanged after the call to your function. So, to have your own copy of the data inside it, you have to create that copy explicitly.

5

Here you try to take stdout from Output (i.e. try to take the ownership of stdout), but because you don't own output (you have a non-mutable reference) and the type of stdout (Vec<u8>) don't implement Copy you cannot do that.

So, you have two options:

  • borrow the value, i.e. take a non-mutable reference to the field : &output.stdout
  • clone the data to obtain a owned version : output.stdout.clone()
1 Like
6

The point is that when you write output.stdout in the way you're doing here, you are performing a move which destroys the original value. You only have a reference, so you're not allowed to destroy output.stdout.

1 Like
7

I believe the function you call, String::from_utf8, takes ownership of it's argument. You are sending in a reference to something you do not own.

8

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