Implement cloned for Option<&mut T>

[Stebalien]

Mirror Option<&T>.cloned().

[rust-highfive]

r? @pcwalton

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[alexcrichton]

This was originally intentionally left to just &T as it was a conservative option and it was unclear how many times you want to call .cloned() on Option<&mut T>. Unfortunately this also makes Option inconsistent with Iterator which also has a similar cloned method.

I'm curious, could you describe your use case for having an Option<&mut T> and then waning to clone it?

[Stebalien]

A test case for a get_mut function. It isn't necessary but it just feels odd that this method is supported for references but not mutable references so I figured this might have been overlooked. What was the rational behind leaving it out?

[Stebalien]

Closing because you're right. Any API that can return an Option<&mut T> should have a non-mut equivalent that returns an Option<&T> and users should be discouraged from requesting mutability/exclusive access when they don't need it.