Implement default values for at() (#995)

1 files changed, 9 insertions, 2 deletions

diff --git a/src/eval/str.rs b/src/eval/str.rs
index 89be3699..d7e00bf6 100644
--- a/src/eval/str.rs
+++ b/src/eval/str.rs
@@ -69,12 +69,13 @@ impl Str {
     }
 
     /// Extract the grapheme cluster at the given index.
-    pub fn at(&self, index: i64) -> StrResult<Self> {
+    pub fn at<'a>(&'a self, index: i64, default: Option<&'a str>) -> StrResult<Self> {
         let len = self.len();
         let grapheme = self.0[self.locate(index)?..]
             .graphemes(true)
             .next()
-            .ok_or_else(|| out_of_bounds(index, len))?;
+            .or(default)
+            .ok_or_else(|| no_default_and_out_of_bounds(index, len))?;
         Ok(grapheme.into())
     }
 
@@ -348,6 +349,12 @@ fn out_of_bounds(index: i64, len: i64) -> EcoString {
     eco_format!("string index out of bounds (index: {}, len: {})", index, len)
 }
 
+/// The out of bounds access error message when no default value was given.
+#[cold]
+fn no_default_and_out_of_bounds(index: i64, len: i64) -> EcoString {
+    eco_format!("no default value was specified and string index out of bounds (index: {}, len: {})", index, len)
+}
+
 /// The char boundary access error message.
 #[cold]
 fn not_a_char_boundary(index: i64) -> EcoString {