firedrakeproject/firedrake — pull request #400 by wence- (2014-11-26 15:14:02+00:00)
Title: Allow assignment into non-mixed FSes from indexed MFSes

Previously, it was not possible to write:

V = FunctionSpace(...)
W = V*V
w = Function(W)
v = Function(V)
w1, w2 = w.split()

v.assign(w1)
v.assign(w2)

Despite the function spaces being compatible. It turns out to be quite
simple to allow, so do so.