創建型別的通用變體的列舉-有解無憂

我有一個帶有常量泛型引數的結構VAR。該引數用于方法中，提高運行時速度，由于大量比較可以在編譯時完成。在任何地方存盤和傳遞泛型型別是相當困難的。我有固定數量的變體，我可以在 enum 中列出SquirrelVariant，我可以更輕松地傳遞，并用于match分支到通用函式。從 a 創建列舉Squirrel<VAR>相當困難，rust 似乎不允許編譯時間match或類似的東西。

struct Squirrel<const VAR: u8>
{
}


enum SquirrelVariant
{
    V1(Squirrel<1>),
    V2(Squirrel<2>),
    V3(Squirrel<3>),
}

// failed attempt 1)
fn make_squirrel_variant<const VAR: u8>(s: Squirrel<VAR>) -> SquirrelVariant
{
    match VAR {
        1 => SquirrelVariant::V1(s), // expected `1_u8`, found `VAR`
        2 => SquirrelVariant::V2(s), // expected `2_u8`, found `VAR`
        3 => SquirrelVariant::V3(s), // expected `3_u8`, found `VAR`
    }
}


// failed attempt 2)
impl From<Squirrel<1>> for SquirrelVariant
{
    fn from(s: Squirrel<1>) -> Self
    {
        SquirrelVariant::V1(s)
    }
}

impl From<Squirrel<2>> for SquirrelVariant
{
    fn from(s: Squirrel<2>) -> Self
    {
        SquirrelVariant::V2(s)
    }
}

impl From<Squirrel<3>> for SquirrelVariant
{
    fn from(s: Squirrel<3>) -> Self
    {
        SquirrelVariant::V3(s)
    }
}

fn make_squirrel_variant2<const VAR: u8>(s: Squirrel<VAR>) -> SquirrelVariant
{
    s.into() // the trait `From<Squirrel<VAR>>` is not implemented for `SquirrelVariant`
    // = help: the following implementations were found:
    //     <SquirrelVariant as From<Squirrel<1_u8>>>
    //     <SquirrelVariant as From<Squirrel<2_u8>>>
    //     <SquirrelVariant as From<Squirrel<3_u8>>>
}

https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=54ec536a9d84d13b4b3ae16180022ba8

uj5u.com熱心網友回復：

您可以使用以下技巧來解決型別錯誤：

struct Squirrel<const VAR: u8> {}

impl<const VAR: u8> Squirrel<VAR> {
    fn transmute_squirrel_type<const VAR2: u8>(self) -> Squirrel<VAR2> {
        if VAR == VAR2 {
            Squirrel { }
        } else {
            unreachable!()
        }
    }
}


enum SquirrelVariant
{
    V1(Squirrel<1>),
    V2(Squirrel<2>),
    V3(Squirrel<3>),
}

impl<const VAR: u8> Squirrel<VAR> {
    fn to_variant(self) -> SquirrelVariant {
        match VAR {
            1 => SquirrelVariant::V1(self.transmute_squirrel_type()),
            2 => SquirrelVariant::V2(self.transmute_squirrel_type()),
            3 => SquirrelVariant::V3(self.transmute_squirrel_type()),
            _ => unreachable!()
        }
    }
}

轉載請註明出處，本文鏈接：https://www.uj5u.com/net/495742.html

標籤：仿制药锈枚举匹配编译时

上一篇：泛型中的約束型別

下一篇：TypeScript無法在函式型別中派生型別約束