Differences between invariant and immutable?

[Jeremie Pelletier]

I upgraded to 2.0.30 today and noticed the new immutable keyword on the migration to shared page. I knew of the keyword before but older versions of DMD didn't seem to recognize it, so I assumed it meant invariant.

But now I'd like to know what are the specific differences between the two, as I couldn't find any detailed page on the subject.

Jeremie