Using BitAnd<T> for truncation on integer types?

[npmccallum]

Would rust be willing to take a pull request that implements BitAnd on integer types for all smaller versions of the int?

For example:

impl BitAnd<u64> for u128 { type Output = u64 }
impl BitAnd<u32> for u128 { type Output = u32 }
impl BitAnd<u16> for u128 { type Output = u16 }
impl BitAnd<u8> for u128 { type Output = u8 }

impl BitAnd<u32> for u64 { type Output = u32 }
impl BitAnd<u16> for u64 { type Output = u16 }
impl BitAnd<u8> for u64 { type Output = u8 }

impl BitAnd<u16> for u32 { type Output = u16 }
impl BitAnd<u8> for u32 { type Output = u8 }

impl BitAnd<u8> for u16 { type Output = u8 }

This would enable effortless, correct and infallible truncation in generic contexts. Is this problem sophisticated enough to warrant an RFC?

[npmccallum]

(The problem of how to handle usize on u32 given its variable size is a corner case...)

[jonas-schievink]

Closing because of the issues encountered with the PR #54442. This can be prototyped in an external library (like cast), and might be addressed by rust-lang/rfcs#2484 as well.