Made FixedSizeList::try_push_valid public and added new_with_field (

#887)

src/array/fixed_size_list/mutable.rs

@@ -3,7 +3,7 @@ use std::sync::Arc;
 use crate::{
     array::{Array, MutableArray, TryExtend, TryPush},
     bitmap::MutableBitmap,
-    datatypes::DataType,
+    datatypes::{DataType, Field},
     error::{ArrowError, Result},
 };
 
@@ -41,6 +41,21 @@ impl<M: MutableArray> MutableFixedSizeListArray<M> {
         }
     }
 
+    /// Creates a new [`MutableFixedSizeListArray`] from a [`MutableArray`] and size.
+    pub fn new_with_field(values: M, name: &str, nullable: bool, size: usize) -> Self {
+        let data_type = DataType::FixedSizeList(
+            Box::new(Field::new(name, values.data_type().clone(), nullable)),
+            size,
+        );
+        assert_eq!(values.len(), 0);
+        Self {
+            size,
+            data_type,
+            values,
+            validity: None,
+        }
+    }
+
     /// The inner values
     pub fn values(&self) -> &M {
         &self.values
@@ -61,7 +76,9 @@ impl<M: MutableArray> MutableFixedSizeListArray<M> {
     }
 
     #[inline]
-    fn try_push_valid(&mut self) -> Result<()> {
+    /// Needs to be called when a valid value was extended to this array.
+    /// This is a relatively low level function, prefer `try_push` when you can.
+    pub fn try_push_valid(&mut self) -> Result<()> {
         if self.values.len() % self.size != 0 {
             return Err(ArrowError::Overflow);
         };

tests/it/array/fixed_size_list/mutable.rs

@@ -1,4 +1,5 @@
 use arrow2::array::*;
+use arrow2::datatypes::{DataType, Field};
 
 #[test]
 fn primitive() {
@@ -24,3 +25,41 @@ fn primitive() {
     let expected = Int32Array::from(vec![None, None, None]);
     assert_eq!(a, &expected)
 }
+
+#[test]
+fn new_with_field() {
+    let data = vec![
+        Some(vec![Some(1i32), Some(2), Some(3)]),
+        Some(vec![None, None, None]),
+        Some(vec![Some(4), None, Some(6)]),
+    ];
+
+    let mut list = MutableFixedSizeListArray::new_with_field(
+        MutablePrimitiveArray::<i32>::new(),
+        "custom_items",
+        false,
+        3,
+    );
+    list.try_extend(data).unwrap();
+    let list: FixedSizeListArray = list.into();
+
+    assert_eq!(
+        list.data_type(),
+        &DataType::FixedSizeList(
+            Box::new(Field::new("custom_items", DataType::Int32, false)),
+            3
+        )
+    );
+
+    let a = list.value(0);
+    let a = a.as_any().downcast_ref::<Int32Array>().unwrap();
+
+    let expected = Int32Array::from(vec![Some(1i32), Some(2), Some(3)]);
+    assert_eq!(a, &expected);
+
+    let a = list.value(1);
+    let a = a.as_any().downcast_ref::<Int32Array>().unwrap();
+
+    let expected = Int32Array::from(vec![None, None, None]);
+    assert_eq!(a, &expected)
+}