rust - 如何避免使用可选message参数的函数的重复代码？

Question

我想编写自己的assert函数，该函数可以有选择地显示一条消息:

fn foo(msg: Option<&str>) {
    if let Some(m) = msg {
        panic!("{} - Something went wrong: {}", m, "additional info");
    } else {
        panic!("Something went wrong: {}", "additional info")
    }
}

如何避免这样的重复代码？如何避免对消息字符串进行多次分配(重新分配)？

Answer 1

不打印时，请使用空字符串。

fn foo(msg: Option<&str>) {
    panic!("{}{}Something went wrong: {}", 
            { if let Some(m) = msg { m } else { "" } },
            { if let Some(_m) = msg { " - " } else { "" } },
            "additional info");
}

在rustfmt之后看起来像这样:

fn foo(msg: Option<&str>) {
    panic!(
        "{}{}Something went wrong: {}",
        {
            if let Some(m) = msg {
                m
            } else {
                ""
            }
        },
        {
            if let Some(_m) = msg {
                " - "
            } else {
                ""
            }
        },
        "additional info"
    );
}