Should union and similar be must_use?

[winksaville]

Yesterday I had a bug in my code, I wanted to add a separate and distinct object to an existing CSG object. I made a noob error and wrote:

o1.union(&o2)

Obviously it must be assigned:

let d = o1.union(&o2)

Otherwise it's a NOP as there are no side effects.

Suggestion, add the #[must_use] attribute to "all" operators that have no side effects.

[timschmidt]

This is probably a good idea. I have also received some input that there is a desire for an API allowing in-place mutation of coordinates, for example during a translation. As that would reduce memory allocations. This feels like a first step in bifurcating the API that way.

[timschmidt]

Done.