首先看看免费的官方Rust书籍The Rust Programming Language，特别是the chapter on enums。

一个月

fn initialize(datastore: DatabaseType) {
    match datastore {
        DatabaseType::Memory => {
            // ...
        }
        DatabaseType::RocksDB => {
            // ...
        }
    }
}

一个月一个月

fn initialize(datastore: DatabaseType) {
    if let DatabaseType::Memory = datastore {
        // ...
    } else {
        // ...
    }
}

==

#[derive(PartialEq)]
enum DatabaseType {
    Memory,
    RocksDB,
}

fn initialize(datastore: DatabaseType) {
    if DatabaseType::Memory == datastore {
        // ...
    } else {
        // ...
    }
}

matches!

此功能自Rust 1.42.0起可用

fn initialize(datastore: DatabaseType) {
    if matches!(datastore, DatabaseType::Memory) {
        // ...
    } else {
        // ...
    }
}

另见：

• How to compare enum without pattern matching
• Read from an enum without pattern matching
• Compare enums only by variant, not value
• https://doc.rust-lang.org/std/macro.matches.html

// A simple example that runs in rust 1.58:
enum Aap {
    Noot(i32, char),
    Mies(String, f64),
}

fn main() {
    let aap: Aap = Aap::Noot(42, 'q');
    let noot: Aap = Aap::Mies(String::from("noot"), 422.0);
    println!("{}", doe(aap));
    println!("{}", doe(noot));
}

fn doe(a: Aap) -> i32 {
    match a {
        Aap::Noot(i, _) => i,
        Aap::Mies(_, f) => f as i32,
    }
}