+
+ /// Try to produce a substring from an existing "base" value and a `&str`.
+ ///
+ /// Returns `None` if `substr` is not part of `value`.
+ pub fn substr_from_str_slice(value: &ScalarRef, substr: &str) -> Result<Option<Scalar>, Error> {
+ let value_bytes = value.pv_bytes();
+ let value_beg = value_bytes.as_ptr() as usize;
+ let value_end = value_beg + value_bytes.len();
+ let value_range = value_beg..value_end;
+
+ let str_bytes = substr.as_bytes();
+ let str_beg = str_bytes.as_ptr() as usize;
+ let str_end = str_beg + str_bytes.len();
+ if !value_range.contains(&str_beg) || !value_range.contains(&str_end) {
+ return Ok(None);
+ }
+
+ // we just checked the ranges:
+ let start = unsafe { str_bytes.as_ptr().offset_from(value_bytes.as_ptr()) as usize };
+ Ok(Some(unsafe {
+ Scalar::from_raw_move(ffi::RSPL_substr(
+ ffi::RSPL_SvREFCNT_inc(value.sv()),
+ start,
+ substr.len(),
+ ))
+ }))
+ }
+