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如何在编译期确定某个类型是不是 Option

 2 years ago
source link: https://privaterookie.github.io/notes/rust/2022-02-17-%E7%BC%96%E8%AF%91%E6%9C%9F%E7%A1%AE%E5%AE%9A%E6%9F%90%E4%B8%AA%E7%B1%BB%E5%9E%8B%E6%98%AF%E4%B8%8D%E6%98%AFOption.html
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如何在编译期确定某个类型是不是 Option

要求不管是 Option<T> 还是 std::option::Option<T>, 抑或是 type A = Option<usize> 都能检测.

有个使用过程宏检测的简单办法, 原理是利用类型为 Option<T> 的变量一定可以被赋值为 None, 否则编译器会报错.

过程宏实现


#[proc_macro]
pub fn assert_option(item: TokenStream) -> TokenStream {
    let ty = parse_macro_input!(item as TypePath);
    let expand = quote! {
        {
            let _: #ty = ::std::option::Option::None;
        }
    };
    TokenStream::from(expanded)
}


type M = Option<u8>;
// 编译成功
assert_option!(M);
// 编译失败
assert_option!(u8);

report

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