jorgecarleitao commented on a change in pull request #8399:
URL: https://github.com/apache/arrow/pull/8399#discussion_r501756230
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File path: rust/datafusion/src/physical_plan/type_coercion.rs
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@@ -16,6 +16,18 @@
// under the License.
//! Type coercion rules for functions with multiple valid signatures
+//!
+//! Coercion is performed automatically by DataFusion when the types
+//! of arguments passed to a function do not exacty match the types
+//! required by that function. In this case, DataFuson will attempt to
+//! *coerce* the arguments to types accepted by the function by
+//! inserting CAST operations.
+//!
+//! CAST operations added by coercion are lossless and never discard
+//! information. For example coercion from i32 -> i64 might be
+//! performed because all valid i32 values can be represented using an
+//! i64. However, i64 -> i32 is never performed as there are i64
Review comment:
```suggestion
//! i64. However, i64 -> i32 requires users to explicitly cast the array as
there are i64
```
##########
File path: rust/datafusion/src/physical_plan/type_coercion.rs
##########
@@ -16,6 +16,18 @@
// under the License.
//! Type coercion rules for functions with multiple valid signatures
+//!
+//! Coercion is performed automatically by DataFusion when the types
+//! of arguments passed to a function do not exacty match the types
+//! required by that function. In this case, DataFuson will attempt to
Review comment:
```suggestion
//! required by that function. In this case, DataFusion will attempt to
```
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