[Variant] Move VariantAsPrimitive to type_conversions.rs (#8321)

# Which issue does this PR close?

* Follow-up to #8280

# Rationale for this change

See #8280 (comment)

# What changes are included in this PR?

See description.

# Are these changes tested?

Code movement. Compilation suffices.

# Are there any user-facing changes?

No.

---------

Co-authored-by: Andrew Lamb <[email protected]>

Author: scovich

parquet-variant-compute/src/type_conversion.rs

@@ -17,6 +17,9 @@
 
 //! Module for transforming a typed arrow `Array` to `VariantArray`.
 
+use arrow::datatypes::{self, ArrowPrimitiveType};
+use parquet_variant::Variant;
+
 /// Options for controlling the behavior of `cast_to_variant_with_options`.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct CastOptions {
@@ -30,6 +33,47 @@ impl Default for CastOptions {
     }
 }
 
+/// Helper trait for converting `Variant` values to arrow primitive values.
+pub(crate) trait VariantAsPrimitive<T: ArrowPrimitiveType> {
+    fn as_primitive(&self) -> Option<T::Native>;
+}
+
+impl VariantAsPrimitive<datatypes::Int32Type> for Variant<'_, '_> {
+    fn as_primitive(&self) -> Option<i32> {
+        self.as_int32()
+    }
+}
+impl VariantAsPrimitive<datatypes::Int16Type> for Variant<'_, '_> {
+    fn as_primitive(&self) -> Option<i16> {
+        self.as_int16()
+    }
+}
+impl VariantAsPrimitive<datatypes::Int8Type> for Variant<'_, '_> {
+    fn as_primitive(&self) -> Option<i8> {
+        self.as_int8()
+    }
+}
+impl VariantAsPrimitive<datatypes::Int64Type> for Variant<'_, '_> {
+    fn as_primitive(&self) -> Option<i64> {
+        self.as_int64()
+    }
+}
+impl VariantAsPrimitive<datatypes::Float16Type> for Variant<'_, '_> {
+    fn as_primitive(&self) -> Option<half::f16> {
+        self.as_f16()
+    }
+}
+impl VariantAsPrimitive<datatypes::Float32Type> for Variant<'_, '_> {
+    fn as_primitive(&self) -> Option<f32> {
+        self.as_f32()
+    }
+}
+impl VariantAsPrimitive<datatypes::Float64Type> for Variant<'_, '_> {
+    fn as_primitive(&self) -> Option<f64> {
+        self.as_f64()
+    }
+}
+
 /// Convert the value at a specific index in the given array into a `Variant`.
 macro_rules! non_generic_conversion_single_value {
     ($array:expr, $cast_fn:expr, $index:expr) => {{

parquet-variant-compute/src/variant_get/output/row_builder.rs

@@ -22,6 +22,7 @@ use arrow::datatypes::ArrowPrimitiveType;
 use arrow::error::{ArrowError, Result};
 use parquet_variant::{Variant, VariantPath};
 
+use crate::type_conversion::VariantAsPrimitive;
 use crate::VariantArrayBuilder;
 
 use std::sync::Arc;
@@ -124,47 +125,6 @@ impl<T: VariantShreddingRowBuilder> VariantShreddingRowBuilder for VariantPathRo
     }
 }
 
-/// Helper trait for converting `Variant` values to arrow primitive values.
-trait VariantAsPrimitive<T: ArrowPrimitiveType> {
-    fn as_primitive(&self) -> Option<T::Native>;
-}
-
-impl VariantAsPrimitive<datatypes::Int32Type> for Variant<'_, '_> {
-    fn as_primitive(&self) -> Option<i32> {
-        self.as_int32()
-    }
-}
-impl VariantAsPrimitive<datatypes::Int16Type> for Variant<'_, '_> {
-    fn as_primitive(&self) -> Option<i16> {
-        self.as_int16()
-    }
-}
-impl VariantAsPrimitive<datatypes::Int8Type> for Variant<'_, '_> {
-    fn as_primitive(&self) -> Option<i8> {
-        self.as_int8()
-    }
-}
-impl VariantAsPrimitive<datatypes::Int64Type> for Variant<'_, '_> {
-    fn as_primitive(&self) -> Option<i64> {
-        self.as_int64()
-    }
-}
-impl VariantAsPrimitive<datatypes::Float16Type> for Variant<'_, '_> {
-    fn as_primitive(&self) -> Option<half::f16> {
-        self.as_f16()
-    }
-}
-impl VariantAsPrimitive<datatypes::Float32Type> for Variant<'_, '_> {
-    fn as_primitive(&self) -> Option<f32> {
-        self.as_f32()
-    }
-}
-impl VariantAsPrimitive<datatypes::Float64Type> for Variant<'_, '_> {
-    fn as_primitive(&self) -> Option<f64> {
-        self.as_f64()
-    }
-}
-
 /// Helper function to get a user-friendly type name
 fn get_type_name<T: ArrowPrimitiveType>() -> &'static str {
     match std::any::type_name::<T>() {