Rust Platform

🎯 grep keeps the lines that match a pattern. Real grep also has flags: -i (ignore case) and -v (invert = keep the non-matches). 

In Python:

def grep(
    text: str, pattern: str, ignore_case: bool = False, invert: bool = False
) -> Generator[str, None, None]:
    lines = text.splitlines()
    if ignore_case:
        pattern = pattern.lower()
    for line in lines:
        hay = line.lower() if ignore_case else line
        found = pattern in hay
        keep = not found if invert else found
        if keep:
            yield line
        # or xor logic
        # if (pattern in hay) != invert:
        #    yield line

Substring test and case folding

line.contains(pattern) is Rust's pattern in line. For case-insensitive matching, you can use .to_lowercase().

A note on the signature - what is 'a ? 

fn grep<'a>(text: &'a str, pattern: &str, ignore_case: bool, invert: bool) -> Vec<&'a str>

In Python, the returned list owns its strings, and the garbage collector (GC) keeps text alive as long …