The substrate has removed as in favor of From/Into. An assumption is made that all types are u32 at least.
Using the trait SimpleArithmatic, the following can be implemented:
From: u8, u16, u32
TryFrom: u64, u128, usize
TryInto: u8, u16, u32, u64, u128, usize
Another trait is also provided to provide ergonomic infallible conversion when you don't care if the value saturates.
UniqueSaturatedInto: u8, u16, u32, u64, u128
UniqueSaturatedFrom: u64, u128
This makes the conversion from u32 to Substrate specific types relatively easy:
pub fn u32_to_balance(input: u32) -> T::Balance {
input.into()
}
For larger types, you need to handle cases where the Balance type for a run-time is smaller than what is available:
pub fn u64_to_balance_option(input: u64) -> Option<T::Balance> {
input.try_into().ok()
}
// Note the warning about saturated conversions
pub fn u64_to_balance_saturated(input: u64) -> T::Balance {
input.saturated_into()
}
While converting from T:Balance to rust primitive, users should also handle conversion between incompatible types:
pub fn balance_to_u64(input: T::Balance) -> Option<u64> {
TryInto::<u64>::try_into(input).ok()
}
For Substrate v1.0
The 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;
}
Here are some working examples:
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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