Function index 

pub fn index(s: &str, line: u32, column: u32) -> usize

Get str byte index of line and column

If the line out the length of the s, return s.len()

Panics

• line by zero

Examples

assert_eq!(index("", 1, 1),             0);
assert_eq!(index("a", 1, 1),            0);
assert_eq!(index("a", 1, 2),            1);
assert_eq!(index("a\n", 1, 2),          1);
assert_eq!(index("a\n", 2, 1),          2);
assert_eq!(index("a\nx", 2, 2),         3);
assert_eq!(index("你好\n世界", 1, 2),   3); // byte index
assert_eq!(index("你好\n世界", 1, 3),   6);
assert_eq!(index("你好\n世界", 2, 1),   7);