Doctest for StructArray. (#562) (#567)

Co-authored-by: Navin <navin@novemberkilo.com>

arrow/src/array/array_struct.rs

@@ -30,6 +30,32 @@ use crate::{
 
 /// A nested array type where each child (called *field*) is represented by a separate
 /// array.
+/// # Example: Create an array from a vector of fields
+///
+/// ```
+/// use std::sync::Arc;
+/// use arrow::array::{Array, ArrayRef, BooleanArray, Int32Array, StructArray};
+/// use arrow::datatypes::{DataType, Field};
+///
+/// let boolean = Arc::new(BooleanArray::from(vec![false, false, true, true]));
+/// let int = Arc::new(Int32Array::from(vec![42, 28, 19, 31]));
+///
+/// let struct_array = StructArray::from(vec![
+///     (
+///         Field::new("b", DataType::Boolean, false),
+///         boolean.clone() as ArrayRef,
+///     ),
+///     (
+///         Field::new("c", DataType::Int32, false),
+///         int.clone() as ArrayRef,
+///     ),
+/// ]);
+/// assert_eq!(struct_array.column(0).as_ref(), boolean.as_ref());
+/// assert_eq!(struct_array.column(1).as_ref(), int.as_ref());
+/// assert_eq!(4, struct_array.len());
+/// assert_eq!(0, struct_array.null_count());
+/// assert_eq!(0, struct_array.offset());
+/// ```
 pub struct StructArray {
     data: ArrayData,
     pub(crate) boxed_fields: Vec<ArrayRef>,