perf!(builtin/string): prevent calculating .length() twice in `subs…

…tring()`
moonbitlang · Dec 26, 2024 · 8341d4d · 8341d4d
1 parent eeff5ad
commit 8341d4d
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Showing 2 changed files with 8 additions and 7 deletions.
diff --git a/builtin/builtin.mbti b/builtin/builtin.mbti
@@ -623,7 +623,7 @@ impl String {
   op_add(String, String) -> String
   op_equal(String, String) -> Bool
   op_get(String, Int) -> Char
-  substring(String, start~ : Int = .., end~ : Int = ..) -> String
+  substring(String, start~ : Int = .., end? : Int) -> String
   to_json(String) -> Json
   to_string(String) -> String
 }

diff --git a/builtin/string.mbt b/builtin/string.mbt
@@ -57,12 +57,13 @@ fn unsafe_substring(str : String, start : Int, end : Int) -> String {
 ///   ignore(s.substring(start=3, end=2))
 /// }
 /// ```
-pub fn substring(
-  self : String,
-  start~ : Int = 0,
-  end~ : Int = self.length()
-) -> String {
-  guard start >= 0 && start <= end && end <= self.length()
+pub fn substring(self : String, start~ : Int = 0, end? : Int) -> String {
+  let len = self.length()
+  let end = match end {
+    Some(end) => end
+    None => len
+  }
+  guard start >= 0 && start <= end && end <= len
   unsafe_substring(self, start, end)
 }