Quicker check constant check in slice (#3259)

Signed-off-by: Joe Isaacs <[email protected]>

---------

Signed-off-by: Joe Isaacs <[email protected]>

Author: joseph-isaacs

vortex-array/src/array/implementation.rs

@@ -12,14 +12,12 @@ use crate::array::convert::IntoArray;
 use crate::array::operations::ArrayOperationsImpl;
 use crate::array::validity::ArrayValidityImpl;
 use crate::array::visitor::ArrayVisitorImpl;
+use crate::arrays::ConstantEncoding;
 use crate::builders::ArrayBuilder;
 use crate::compute::{ComputeFn, InvocationArgs, Output};
 use crate::stats::{Precision, Stat, StatsProviderExt, StatsSetRef};
-use crate::vtable::VTableRef;
-use crate::{
-    Array, ArrayRef, ArrayStatistics, ArrayStatisticsImpl, ArrayVisitor, Canonical, Encoding,
-    EncodingId,
-};
+use crate::vtable::{EncodingVTable, VTableRef};
+use crate::{Array, ArrayRef, ArrayStatisticsImpl, ArrayVisitor, Canonical, Encoding, EncodingId};
 
 /// A trait used to encapsulate common implementation behaviour for a Vortex [`Array`].
 pub trait ArrayImpl:
@@ -115,9 +113,8 @@ impl<A: ArrayImpl + 'static> Array for A {
 
         // We know that constant array don't need stats propagation, so we can avoid the overhead of
         // computing derived stats and merging them in.
-        // TODO(ngates): skip the is_constant check here, it can force an expensive compute.
         // TODO(ngates): provide a means to slice an array _without_ propagating stats.
-        let derived_stats = (!self.is_constant()).then(|| {
+        let derived_stats = (!self.is_encoding(ConstantEncoding.id())).then(|| {
             let stats = self.statistics().to_owned();
 
             // an array that is not constant can become constant after slicing