Idea: Implement constraints on geometry types

[frewsxcv]

Examples:

• LineString: panics if fewer than two points
• Polygon: panics if any rings has fewer than three points
• Polygon should check if first+last points are the same?
• Polygon should ensure interiors are inside exterior? Maybe not this is one as it might be expensive.

[TeXitoi]

Checks that the inners don't intersect.

Checks that multi don't intersect.

[TeXitoi]

Maybe that can be an algorithm "check" or something like that. ie optional.

[urschrei]

Shapely will allow you to construct invalid Polygons (rings that cross each other, and touch at more than one point), but raises exceptions when they're used, presumably for performance reasons. Maybe a Valid trait that returns a bool, which could be checked by any methods implemented on the type.
How would the more straightforward constructors look? Something like

impl<T> LineString
where T: Float {
    pub fn new(v: Vec<T>) -> Result(LineString, _) {
        // Check that the vec contains at least two elements?
        // I have no idea what happens next
    }
}

?
(I've never written a "validating" constructor before, so I have no idea what I'm doing, really – if anyone's got some examples that would be great)

[frewsxcv]

One example in std is CString::new which will fail if the bytes contain a null character (\0)

[frewsxcv]

Opened an issue similar to this: #127