Function builtin_substr_assign 

fn builtin_substr_assign(
    args: &[RValue],
    _named: &[(String, RValue)],
) -> Result<RValue, RError>

Replace substrings in character strings.

Vectorized over x, with start, stop, and value recycled.

@param x character vector (modified in place conceptually) @param start integer vector of start positions (1-based) @param stop integer vector of stop positions (1-based) @param value character vector of replacement strings @return character vector with substrings replaced