如何在特定于基材的类型和Rust原语类型之间转换?

问题描述

使用Substrate区块链框架，如何在Substrate特定类型和Rust原语类型之间进行转换，反之亦然?

Using the Substrate blockchain framework, how can I convert between Substrate specific types and Rust primitive types and vice versa?

例如:

• 将时间(T::Moment)转换为u64
• 将u64转换为T::Balance

• Convert a time (T::Moment) to a u64
• Convert a u64 to a T::Balance

等...

推荐答案

获取最新的Substrate master

基板已已删除As ，而赞成使用From/. 假定所有类型至少为u32.

For the latest in Substrate master

Substrate has removed As in favor of From/Into. An assumption is made that all types are at least u32.

根据特征SimpleArithmatic，实现了以下内容:

From the trait SimpleArithmatic, the following are implemented:

• From:u8，u16，u32
• TryFrom:u64，u128，usize
• TryInto:u8，u16，u32，u64，u128，usize

• From: u8, u16, u32
• TryFrom: u64, u128, usize
• TryInto: u8, u16, u32, u64, u128, usize

还提供了另一个特征以提供人体工程学当您不在乎该值是否饱和时，就可以进行无误的转换.

Another trait is also provided to provide ergonomicinfallible conversion when you don't care if the value saturates.

• UniqueSaturatedInto:u8，u16，u32，u64，u128
• UniqueSaturatedFrom:u64，u128

• UniqueSaturatedInto: u8, u16, u32, u64, u128
• UniqueSaturatedFrom: u64, u128

SaturatedConversion(saturated_into和saturated_from).我唯一想到的是，这种情况在运行时算法中很深，在逻辑上可以确定它不会溢出，但是不能提供证明，因为它将取决于一致的预先存在的状态.

SaturatedConversion (saturated_into and saturated_from) should not be used unless you know what you're doing, you've thought and considered all options and your use-case implies that saturation is fundamentally correct. The only time I imagine this is the case is deep in runtime arithmetic where you are logically certain it will not overflow, but can't provide a proof because it would depend on consistent pre-existing state.

这意味着从u32到承印物特定类型的工作应该很容易:

This means that working from u32 to Substrate specific types should be easy:

pub fn u32_to_balance(input: u32) -> T::Balance {
    input.into()
}

对于较大的类型，您需要处理运行时Balance类型小于可用类型的情况:

For larger types, you need to handle the case where the Balance type for a runtime is smaller than what is available:

pub fn u64_to_balance_option(input: u64) -> Option<T::Balance> {
    input.try_into().ok()
}

// Note the warning above about saturated conversions
pub fn u64_to_balance_saturated(input: u64) -> T::Balance {
    input.saturated_into()
}

从T::Balance转换为rust原语时，还需要处理不兼容类型之间的转换:

When converting from T::Balance to a rust primitive, you need to also handle conversion between incompatible types:

pub fn balance_to_u64(input: T::Balance) -> Option<u64> {
    TryInto::<u64>::try_into(input).ok()
}

// Note the warning above about saturated conversions
pub fn balance_to_u64_saturated(input: T::Balance) -> u64 {
    input.saturated_into::<u64>()
}

---

对于基材v1.0

基板在sr-primitives板条箱中提供 pub trait As<T> :

---

For Substrate v1.0

Substrate provides pub trait As<T> in the sr-primitives crate:

/// Simple trait similar to `Into`, except that it can be used to convert numerics between each
/// other.
pub trait As<T> {
    /// Convert forward (ala `Into::into`).
    fn as_(self) -> T;
    /// Convert backward (ala `From::from`).
    fn sa(_: T) -> Self;
}

以下是一些如何使用它的有效示例:

Here are some working examples of how it can be used:

impl<T: Trait> Module<T> {
    // `as_` will turn T::Balance into a u64
    pub fn balance_to_u64(input: T::Balance) -> u64 {
        input.as_()
    }

    // Being explicit, you can convert a `u64` to a T::Balance
    // using the `As` trait, with `T: u64`, and then calling `sa`
    pub fn u64_to_balance(input: u64) -> T::Balance {
        <T::Balance as As<u64>>::sa(input)
    }

    // You can also let Rust figure out what `T` is
    pub fn u64_to_balance_implied(input: u64) -> T::Balance {
        <T::Balance as As<_>>::sa(input)
    }

    // You can also let Rust figure out where `sa` is implemented
    pub fn u64_to_balance_implied_more(input: u64) -> T::Balance {
        T::Balance::sa(input)
    }
}

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