From 2a8a8c00f5a528485fa6cbf88c5f6a0168310a6a Mon Sep 17 00:00:00 2001
From: Stephen Chung <schungx@live.com>
Date: Sat, 15 Jan 2022 10:24:08 +0800
Subject: [PATCH] Refine calc_index API.

---
 src/eval/chaining.rs | 20 +++++++++++---------
 src/eval/target.rs   | 26 +++++++++++++-------------
 2 files changed, 24 insertions(+), 22 deletions(-)

diff --git a/src/eval/chaining.rs b/src/eval/chaining.rs
index 3a776af9..6ac788fd 100644
--- a/src/eval/chaining.rs
+++ b/src/eval/chaining.rs
@@ -790,8 +790,9 @@ impl Engine {
                     .as_int()
                     .map_err(|typ| self.make_type_mismatch_err::<crate::INT>(typ, pos))?;
                 let len = arr.len();
-                let arr_idx =
-                    calc_index(len, index, true, || ERR::ErrorArrayBounds(len, index, pos))?;
+                let arr_idx = calc_index(len, index, true, || {
+                    ERR::ErrorArrayBounds(len, index, pos).into()
+                })?;
 
                 Ok(arr.get_mut(arr_idx).map(Target::from).unwrap())
             }
@@ -803,8 +804,9 @@ impl Engine {
                     .as_int()
                     .map_err(|typ| self.make_type_mismatch_err::<crate::INT>(typ, pos))?;
                 let len = arr.len();
-                let arr_idx =
-                    calc_index(len, index, true, || ERR::ErrorArrayBounds(len, index, pos))?;
+                let arr_idx = calc_index(len, index, true, || {
+                    ERR::ErrorArrayBounds(len, index, pos).into()
+                })?;
 
                 let value = arr.get(arr_idx).map(|&v| (v as crate::INT).into()).unwrap();
 
@@ -844,10 +846,10 @@ impl Engine {
                     let end = range.end;
 
                     let start = calc_index(BITS, start, false, || {
-                        ERR::ErrorBitFieldBounds(BITS, start, pos)
+                        ERR::ErrorBitFieldBounds(BITS, start, pos).into()
                     })?;
                     let end = calc_index(BITS, end, false, || {
-                        ERR::ErrorBitFieldBounds(BITS, end, pos)
+                        ERR::ErrorBitFieldBounds(BITS, end, pos).into()
                     })?;
 
                     if end <= start {
@@ -869,10 +871,10 @@ impl Engine {
                     let end = *range.end();
 
                     let start = calc_index(BITS, start, false, || {
-                        ERR::ErrorBitFieldBounds(BITS, start, pos)
+                        ERR::ErrorBitFieldBounds(BITS, start, pos).into()
                     })?;
                     let end = calc_index(BITS, end, false, || {
-                        ERR::ErrorBitFieldBounds(BITS, end, pos)
+                        ERR::ErrorBitFieldBounds(BITS, end, pos).into()
                     })?;
 
                     if end < start {
@@ -913,7 +915,7 @@ impl Engine {
                 const BITS: usize = std::mem::size_of::<crate::INT>() * 8;
 
                 let bit = calc_index(BITS, index, true, || {
-                    ERR::ErrorBitFieldBounds(BITS, index, pos)
+                    ERR::ErrorBitFieldBounds(BITS, index, pos).into()
                 })?;
 
                 let bit_value = (*value & (1 << bit)) != 0;
diff --git a/src/eval/target.rs b/src/eval/target.rs
index e8efefb9..4209c3fa 100644
--- a/src/eval/target.rs
+++ b/src/eval/target.rs
@@ -1,7 +1,7 @@
 //! Type to hold a mutable reference to the target of an evaluation.
 
 use crate::types::dynamic::Variant;
-use crate::{Dynamic, EvalAltResult, RhaiResultOf, INT};
+use crate::{Dynamic, RhaiResultOf, INT};
 use std::ops::{Deref, DerefMut};
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
@@ -38,35 +38,35 @@ pub fn calc_offset_len(length: usize, start: INT, len: INT) -> (usize, usize) {
 //
 // Negative starting positions count from the end.
 //
-// Values going over bounds call the provided closure to create an error.
+// Values going over bounds call the provided closure to return a default value or an error.
 #[inline(always)]
-pub fn calc_index(
+pub fn calc_index<E>(
     length: usize,
     start: INT,
     negative_count_from_end: bool,
-    err: impl Fn() -> EvalAltResult,
-) -> RhaiResultOf<usize> {
+    err: impl Fn() -> Result<usize, E>,
+) -> Result<usize, E> {
     if start < 0 {
         if negative_count_from_end {
             // Count from end if negative
             #[cfg(not(feature = "unchecked"))]
-            return start
-                .checked_abs()
-                .ok_or_else(|| err().into())
-                .and_then(|positive_start| {
+            return match start.checked_abs() {
+                Some(positive_start) => {
                     if (positive_start as usize) > length {
-                        Err(err().into())
+                        err()
                     } else {
                         Ok(length - (positive_start as usize))
                     }
-                });
+                }
+                None => err(),
+            };
             #[cfg(feature = "unchecked")]
             return Ok(length - (start.abs() as usize));
         } else {
-            Err(err().into())
+            err()
         }
     } else if start as usize >= length {
-        Err(err().into())
+        err()
     } else {
         Ok(start as usize)
     }