fix details

Signed-off-by: martinvuyk <[email protected]>

stdlib/src/utils/string_slice.mojo

@@ -675,6 +675,7 @@ struct StringSlice[
         Returns:
             The joined string.
         """
+
         # TODO(#3403): Simplify this when the linked conditional conformance
         # feature is added.  Runs a faster algorithm if the concrete types are
         # able to be converted to a span of bytes.
@@ -715,36 +716,35 @@ struct StringSlice[
         Returns:
             The joined string.
         """
+
         var n_elems = len(elems)
         if n_elems == 0:
             return String("")
-        var len_self = self.byte_length()
+        var s_len = self.byte_length()
         var len_elems = 0
         # Calculate the total size of the elements to join beforehand
         # to prevent alloc syscalls as we know the buffer size.
         # This can hugely improve the performance on large lists
         for e_ref in elems:
             len_elems += len(e_ref[].as_bytes_read())
-        var capacity = len_self * (n_elems - 1) + len_elems
+        var capacity = s_len * (n_elems - 1) + len_elems
         var buf = Self._buffer_type(capacity=capacity)
-        var self_ptr = self.unsafe_ptr()
-        var ptr = buf.unsafe_ptr()
+        var s_ptr = self.unsafe_ptr()
+        var b_ptr = buf.unsafe_ptr()
         var offset = 0
         var i = 0
-        var is_first = True
+        var not_first = False
         while i < n_elems:
-            if is_first:
-                is_first = False
-            else:
-                memcpy(dest=ptr + offset, src=self_ptr, count=len_self)
-                offset += len_self
+            memcpy(dest=b_ptr + offset, src=s_ptr, count=s_len * int(not_first))
+            offset += s_len * int(not_first)
+            not_first = True
             var e = elems[i].as_bytes_read()
             var e_len = len(e)
-            memcpy(dest=ptr + offset, src=e.unsafe_ptr(), count=e_len)
+            memcpy(dest=b_ptr + offset, src=e.unsafe_ptr(), count=e_len)
             offset += e_len
             i += 1
         buf.size = capacity
-        buf.unsafe_set(capacity, 0)
+        b_ptr[capacity] = 0
         return String(buf^)
 
     fn splitlines(self, keepends: Bool = False) -> List[String]: