Refactoring variable assignment thru if let block with Enum

Question

I'm working with the code below, which works, but is clearly not a very clever or efficient way to write a value to res.

let mut res = "";
if let Video(n) = res_info {    // res_info represents reference to &Settings type
    if n.pixel_width > 1920{
         res = "2160p";
    }
    else{
        res = "1080p";
    }
}

Printing res_info would yield the following:

Video(Video { pixel_width: 1920, pixel_height: 1080})

The following code seems to be close, however it's not assigning &str to res. I would much prefer a codeblock like this, in which res is only declared once.

let res = if let Video(n) = res_info {
    if n.pixel_width > 1920 {
        "2160p";
    }
    else{
        "1080p";
    }
};

Answer 1

As per the unit documentation

The semicolon ; can be used to discard the result of an expression at the end of a block, making the expression (and thus the block) evaluate to ()

Removing the semicolon should stop value from being discarded so the &str is resolved from the if blocks.

let res = if let Video(n) = res_info {
    if n.pixel_width > 1920{
         "2160p"
    } else{
        "1080p"
    }
}else{
    panic!("res_info is not a Video")
};

or with a match statement might be cleaner

let res = match res_info {
    Video(n) if n.pixel_width > 1920 => "2160p",
    Video(n) => "1080p",
    _ => panic!("res_info is not a Video")
};