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Add matches_prefix function to MultiLocation and Junctions #4827

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Add matches_prefix function to MultiLocation and Junctions #4827

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25 changes: 25 additions & 0 deletions xcm/src/v0/multi_location.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -367,6 +367,31 @@ impl MultiLocation {
return self.at(prefix.len())
}

/// Returns whether `self` begins with or is equal to `prefix`.
///
/// # Example
/// ```rust
/// # use xcm::v0::{Junction::*, MultiLocation::*};
/// # fn main() {
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Suggested change
/// # fn main() {

Rust does this automatically

/// let m = X4(Parent, PalletInstance(3), OnlyChild, OnlyChild);
/// assert!(m.matches_prefix(&X2(Parent, PalletInstance(3))));
/// assert!(m.matches_prefix(&m));
/// assert!(!m.matches_prefix(&X2(Parent, GeneralIndex(99))));
/// assert!(!m.matches_prefix(&X1(PalletInstance(3))));
/// # }
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/// # }

/// ```
pub fn matches_prefix(&self, prefix: &MultiLocation) -> bool {
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pub fn matches_prefix(&self, prefix: &MultiLocation) -> bool {
pub fn starts_with(&self, prefix: &MultiLocation) -> bool {

Sounds more like the other methods available in rust

if self.len() < prefix.len() {
return false
}
for i in 0..prefix.len() {
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for i in 0..prefix.len() {
prefix.iter().zip(self.iter()).all(|l, r| l == r)

This could be used to replace the rest of the function

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That's how I implemented it in Cumulus, but here I figured I'd keep to the imperative style of match_and_split 😄
Can definitely do.

if prefix.at(i) != self.at(i) {
return false
}
}
true
}

/// Mutates `self`, suffixing it with `new`. Returns `Err` in case of overflow.
pub fn push(&mut self, new: Junction) -> result::Result<(), ()> {
let mut n = MultiLocation::Null;
Expand Down
48 changes: 47 additions & 1 deletion xcm/src/v1/multilocation.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -253,6 +253,26 @@ impl MultiLocation {
self.interior.match_and_split(&prefix.interior)
}

/// Returns whether `self` has the same number of parents as `prefix` and its junctions begins
/// with the junctions of `prefix`.
///
/// # Example
/// ```rust
/// # use xcm::v1::{Junctions::*, Junction::*, MultiLocation};
/// # fn main() {
/// let m = MultiLocation::new(1, X3(PalletInstance(3), OnlyChild, OnlyChild));
/// assert!(m.matches_prefix(&MultiLocation::new(1, X1(PalletInstance(3)))));
/// assert!(!m.matches_prefix(&MultiLocation::new(1, X1(GeneralIndex(99)))));
/// assert!(!m.matches_prefix(&MultiLocation::new(0, X1(PalletInstance(3)))));
/// # }
/// ```
pub fn matches_prefix(&self, prefix: &MultiLocation) -> bool {
if self.parents != prefix.parents {
return false
}
self.interior.matches_prefix(&prefix.interior)
}

/// Mutate `self` so that it is suffixed with `suffix`.
///
/// Does not modify `self` and returns `Err` with `suffix` in case of overflow.
Expand Down Expand Up @@ -809,7 +829,33 @@ impl Junctions {
return None
}
}
return self.at(prefix.len())
self.at(prefix.len())
}

/// Returns whether `self` begins with or is equal to `prefix`.
///
/// # Example
/// ```rust
/// # use xcm::v1::{Junctions::*, Junction::*};
/// # fn main() {
/// let mut j = X3(Parachain(2), PalletInstance(3), OnlyChild);
/// assert!(j.matches_prefix(&X2(Parachain(2), PalletInstance(3))));
/// assert!(j.matches_prefix(&j));
/// assert!(j.matches_prefix(&X1(Parachain(2))));
/// assert!(!j.matches_prefix(&X1(Parachain(999))));
/// assert!(!j.matches_prefix(&X4(Parachain(2), PalletInstance(3), OnlyChild, OnlyChild)));
/// # }
/// ```
pub fn matches_prefix(&self, prefix: &Junctions) -> bool {
if self.len() < prefix.len() {
return false
}
for i in 0..prefix.len() {
if prefix.at(i) != self.at(i) {
return false
}
}
true
}
}

Expand Down