I suggest to add something like this to D2 Phobos (this is D1 code):

template Chainable() {
        Chain!(typeof(this), Range) opCat(Range)(Range r) {
            return chain(this, r);
        }
}


Then in the body of a lazy range both Phobos ones like map, filter, zip, iota, and so on, and user-defined ones, you may add:

mixin Chainable;


This allows to write more natural and readable code like:
iota(5) ~ filter!q{a}([1,0,3])
map!abs([1,2,-5]) ~ [10, 20]

instead of more noisy:
chain(iota(5), filter!q{a}([1,0,3]))
chain(map!abs([1,2,-5]), [10, 20])

See also bug 5638 for an useful optimization.