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digitalmars.D.learn - Is InputRange intentionally more restrictive than isInputRange?

I recently required a function to return an input range over some 
base element type E. I was under the impression that this is 
exactly what the interfaces in std.range.interface are for but 
found that these are more restrictive than the checks from 

In particular, isInputRange(R) only requires R to implement 
front, empty and popFront, while InputRange!E requires moveFront 
and opApply in addition. To me this was unexpected and seems 
inconsistent, but maybe there's a good reason for that.

Can someone explain whether (and why) this is intentional.
Dec 22 2018