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11 changes: 10 additions & 1 deletion crates/storage/src/lazy/mapping.rs
Original file line number Diff line number Diff line change
Expand Up @@ -38,12 +38,21 @@ use ink_primitives::Key;

/// A mapping of key-value pairs directly into contract storage.
#[cfg_attr(feature = "std", derive(scale_info::TypeInfo))]
#[derive(Default)]
pub struct Mapping<K, V> {
offset_key: Key,
_marker: PhantomData<fn() -> (K, V)>,
}

/// We implement this manually because the derived implementation adds trait bounds.
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What additional trait bounds are added here?

I checked the cargo-expand-ed contracts using both versions and there was no difference between them.

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@athei athei Dec 10, 2021

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The Default derive requires Default for each type parameter. But for this Mapping we don't need these bounds. In substrate we have a DefaultNoBounds derive for this.

impl<K, V> Default for Mapping<K, V> {
fn default() -> Self {
Self {
offset_key: Default::default(),
_marker: Default::default(),
}
}
}

impl<K, V> core::fmt::Debug for Mapping<K, V> {
fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
f.debug_struct("Mapping")
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