alamb commented on code in PR #16317:
URL: https://github.com/apache/datafusion/pull/16317#discussion_r2134620674
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datafusion/expr/src/expr.rs:
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@@ -413,6 +413,162 @@ impl<'a> TreeNodeContainer<'a, Self> for Expr {
}
}
+/// Literal metadata
+///
+/// Stores metadata associated with a literal expressions
+/// and is designed to be fast to `clone`.
+///
+/// This structure is used to store metadata associated with a literal
expression, and it
+/// corresponds to the `metadata` field on [`Field`].
+///
+/// # Example: Create [`FieldMetadata`] from a [`Field`]
+/// ```
+/// # use std::collections::HashMap;
+/// # use datafusion_expr::expr::FieldMetadata;
+/// # use arrow::datatypes::{Field, DataType};
+/// # let field = Field::new("c1", DataType::Int32, true)
+/// # .with_metadata(HashMap::from([("foo".to_string(), "bar".to_string())]));
+/// // Create a new `FieldMetadata` instance from a `Field`
+/// let metadata = FieldMetadata::new_from_field(&field);
+/// // There is also a `From` impl:
+/// let metadata = FieldMetadata::from(&field);
+/// ```
+///
+/// # Example: Update a [`Field`] with [`FieldMetadata`]
+/// ```
+/// # use datafusion_expr::expr::FieldMetadata;
+/// # use arrow::datatypes::{Field, DataType};
+/// # let field = Field::new("c1", DataType::Int32, true);
+/// # let metadata = FieldMetadata::new_from_field(&field);
+/// // Add any metadata from `FieldMetadata` to `Field`
+/// let updated_field = metadata.add_to_field(field);
+/// ```
+///
+#[derive(Clone, PartialEq, Eq, PartialOrd, Hash, Debug)]
+pub struct FieldMetadata {
+ /// The inner metadata of a literal expression, which is a map of string
+ /// keys to string values.
+ ///
+ /// Note this is not a `HashMap because `HashMap` does not provide
+ /// implementations for traits like `Debug` and `Hash`.
+ inner: Arc<BTreeMap<String, String>>,
+}
+
+impl FieldMetadata {
+ /// Create a new empty metadata instance.
+ pub fn new_empty() -> Self {
+ Self {
+ inner: Arc::new(BTreeMap::new()),
+ }
+ }
Review Comment:
Done in
https://github.com/apache/datafusion/pull/16317/commits/c2759e9b06f352d40e6f13ded3f1e9094095ee62
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