alamb commented on code in PR #10075:
URL: https://github.com/apache/arrow-rs/pull/10075#discussion_r3364769886
##########
arrow-schema/src/extension/canonical/variable_shape_tensor.rs:
##########
@@ -632,20 +621,16 @@ mod tests {
],
false,
)
- .with_metadata(
- [
- (
- EXTENSION_TYPE_NAME_KEY.to_owned(),
- VariableShapeTensor::NAME.to_owned(),
- ),
- (
- EXTENSION_TYPE_METADATA_KEY.to_owned(),
- r#"{ "dim_names": [1, null, 3, 4] }"#.to_owned(),
- ),
- ]
- .into_iter()
- .collect(),
- );
+ .with_metadata([
+ (
+ EXTENSION_TYPE_NAME_KEY,
+ VariableShapeTensor::NAME.to_owned(),
Review Comment:
You may not need the `to_owned()`:
```rust
.with_metadata([
(
EXTENSION_TYPE_NAME_KEY,
VariableShapeTensor::NAME,
),
(
EXTENSION_TYPE_METADATA_KEY,
r#"{ "dim_names": [1, null, 3, 4] }"#,
),
]);
```
##########
arrow-schema/src/metadata.rs:
##########
@@ -0,0 +1,454 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements. See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership. The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use std::collections::{BTreeMap, HashMap, btree_map};
+use std::fmt;
+use std::ops::Index;
+use std::sync::Arc;
+
+/// A cheaply clonable map of key-value metadata, used by
+/// [`Field`](crate::Field) and [`Schema`](crate::Schema).
+///
+/// Cloning a `Metadata` is always cheap, as the underlying map is
+/// reference-counted. Mutating a shared `Metadata` (e.g. via
+/// [`Metadata::insert`]) will clone the underlying map if (and only if)
+/// it is shared (copy-on-write).
+///
+/// The entries are stored in a [`BTreeMap`], so iteration order is
+/// deterministic (sorted by key).
+///
+/// # Example
+/// ```
+/// # use arrow_schema::Metadata;
+/// let mut metadata = Metadata::new();
+/// metadata.insert("key", "value");
+///
+/// let clone = metadata.clone(); // cheap
+/// assert_eq!(clone.get("key"), Some(&"value".to_string()));
+///
+/// // Mutating one does not affect the other:
Review Comment:
As a follow on PR it might be cool to add a builder style API too:
```rust
let metadata = Metadata::builder()
.with("key3", "value3")
.build()
```
That way then we could write
```rust
.with_metadata([
(
EXTENSION_TYPE_NAME_KEY,
VariableShapeTensor::NAME.to_owned(),
),
(
EXTENSION_TYPE_METADATA_KEY,
r#"{ "dim_names": [1, null, 3, 4] }"#.to_owned(),
),
```
something like
```rust
.with_metadata(Metadata::builder()
.with(EXTENSION_TYPE_NAME_KEY, VariableShapeTensor::NAME),
.with(EXTENSION_TYPE_METADATA_KEY)
.build()
)
```
##########
arrow-schema/src/metadata.rs:
##########
@@ -0,0 +1,454 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements. See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership. The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use std::collections::{BTreeMap, HashMap, btree_map};
+use std::fmt;
+use std::ops::Index;
+use std::sync::Arc;
+
+/// A cheaply clonable map of key-value metadata, used by
+/// [`Field`](crate::Field) and [`Schema`](crate::Schema).
+///
+/// Cloning a `Metadata` is always cheap, as the underlying map is
+/// reference-counted. Mutating a shared `Metadata` (e.g. via
+/// [`Metadata::insert`]) will clone the underlying map if (and only if)
+/// it is shared (copy-on-write).
+///
+/// The entries are stored in a [`BTreeMap`], so iteration order is
+/// deterministic (sorted by key).
+///
+/// # Example
+/// ```
+/// # use arrow_schema::Metadata;
+/// let mut metadata = Metadata::new();
+/// metadata.insert("key", "value");
+///
+/// let clone = metadata.clone(); // cheap
+/// assert_eq!(clone.get("key"), Some(&"value".to_string()));
+///
+/// // Mutating one does not affect the other:
+/// metadata.insert("key2", "value2");
+/// assert_eq!(metadata.len(), 2);
+/// assert_eq!(clone.len(), 1);
+/// ```
+#[derive(Clone, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct Metadata(
+ // Invariant: the inner map is never empty (`None` encodes the empty map).
+ // This ensures the derived implementations of `PartialEq`, `Ord`, `Hash`,
…
+ // treat an empty `Metadata` consistently, and the empty case never
allocates.
+ Option<Arc<BTreeMap<String, String>>>,
Review Comment:
It might also be mentioning again here that it uses a BTreeMap to ensure
consistent iteration order
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