Add support for ListView

.gitignore

@@ -7,3 +7,4 @@
 node_modules
 test-ledger
 dist
+.idea

pod/src/error.rs

@@ -1,5 +1,8 @@
 //! Error types
-use solana_program_error::{ProgramError, ToStr};
+use {
+    solana_program_error::{ProgramError, ToStr},
+    std::num::TryFromIntError,
+};
 
 /// Errors that may be returned by the spl-pod library.
 #[repr(u32)]
@@ -22,6 +25,9 @@ pub enum PodSliceError {
     /// Provided byte buffer too large for expected type
     #[error("Provided byte buffer too large for expected type")]
     BufferTooLarge,
+    /// An integer conversion failed because the value was out of range for the target type
+    #[error("An integer conversion failed because the value was out of range for the target type")]
+    ValueOutOfRange,
 }
 
 impl From<PodSliceError> for ProgramError {
@@ -36,6 +42,13 @@ impl ToStr for PodSliceError {
             PodSliceError::CalculationFailure => "Error in checked math operation",
             PodSliceError::BufferTooSmall => "Provided byte buffer too small for expected type",
             PodSliceError::BufferTooLarge => "Provided byte buffer too large for expected type",
+            PodSliceError::ValueOutOfRange => "An integer conversion failed because the value was out of range for the target type"
         }
     }
 }
+
+impl From<TryFromIntError> for PodSliceError {
+    fn from(_: TryFromIntError) -> Self {
+        PodSliceError::ValueOutOfRange
+    }
+}

pod/src/lib.rs

@@ -2,8 +2,10 @@
 
 pub mod bytemuck;
 pub mod error;
+pub mod list;
 pub mod option;
 pub mod optional_keys;
+pub mod pod_length;
 pub mod primitives;
 pub mod slice;
 

pod/src/list/list_trait.rs

@@ -0,0 +1,44 @@
+use {
+    crate::{list::ListView, pod_length::PodLength},
+    bytemuck::Pod,
+    solana_program_error::ProgramError,
+    std::slice::Iter,
+};
+
+/// A trait to abstract the shared, read-only behavior
+/// between `ListViewReadOnly` and `ListViewMut`.
+pub trait List {
+    /// The type of the items stored in the list.
+    type Item: Pod;
+    /// Length prefix type used (`PodU16`, `PodU32`, …).
+    type Length: PodLength;
+
+    /// Returns the number of items in the list.
+    fn len(&self) -> usize;
+
+    /// Returns `true` if the list contains no items.
+    fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Returns the total number of items that can be stored in the list.
+    fn capacity(&self) -> usize;
+
+    /// Returns a read-only slice of the items currently in the list.
+    fn as_slice(&self) -> &[Self::Item];
+
+    /// Returns a read-only iterator over the list.
+    fn iter(&self) -> Iter<'_, Self::Item> {
+        self.as_slice().iter()
+    }
+
+    /// Returns the number of **bytes currently occupied** by the live elements
+    fn bytes_used(&self) -> Result<usize, ProgramError> {
+        ListView::<Self::Item, Self::Length>::size_of(self.len())
+    }
+
+    /// Returns the number of **bytes reserved** by the entire backing buffer.
+    fn bytes_allocated(&self) -> Result<usize, ProgramError> {
+        ListView::<Self::Item, Self::Length>::size_of(self.capacity())
+    }
+}