CODEWITHSUNDEEP
rustenumspattern-matching
ArekBulski
ArekBulski

Reputation: 5098

Matching on enum : First arm unexpectedly always matching

I have a wierdest case yet on my hands. I have an enum that I convert to a string. The enum provided is eg. Green so the string returned from the match is "text-success". Simple right? Turns out that the string returned is always "" regardless of how I obtain it. This makes no sense to me. Please help!

fn bootstrap_table_color (e: Color) -> String {
    let s: String = match &e {
        White => "".to_string(),
        Blue => String::from("table-info"),
        Green => "table-success".to_string(),
        Yellow => "table-warning".to_string(),
        Red => "table-danger".to_string(),
    };
    println!("bootstrap_table_color ({:?}) -> {:?}", e, s);
    return s;
}

bootstrap_table_color (Blue) -> ""
bootstrap_table_color (Green) -> ""

Upvotes: 1

Views: 528

Answers (1)

Denys Séguret
Denys Séguret

Reputation: 382150

That's because all possible values match the White variable arm.

You could see it by doing

let s: String = match &e {
    White => format!("White={:?}", White),
}

The clean solution is to prefix arm values with your enum name:

let s = match &e {
    Color::White => "".to_string(),
    Color::Blue => String::from("table-info"),
    Color::Green => "table-success".to_string(),
    Color::Yellow => "table-warning".to_string(),
    Color::Red => "table-danger".to_string(),
};

Another solution would be to do a use Color::*; but you would be vulnerable to typos or changes.

Upvotes: 4

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