It's often because these functions have unnamed types. Chain of lazy computations in D often return unnamed types (so called "Voldemort" types) because finding good names for those inner structs is a challenge, they have a single use (which is to have a particular signature).
> Chain of lazy computations in D often return unnamed types (so called "Voldemort" types) because finding good names for those inner structs is a challenge
There is something so absurd about having "unnamed types" as an antipattern!
Not really - the concrete type isn't important, but what you can do with it is. One could argue that instead we'd use a concept in place of `auto`, and Bjarne has argued exactly that for C++.
> Not really - the concrete type isn't important, but what you can do with it is.
Then surely that's what should be shown? Rust uses `impl <Trait>` for that, the actual return type is opaque but you know it implements the specified trait.
Not everything is worth naming, if there isn't an obvious good name for somethink (like say, a Java Anonymous Classes) then why not allow it to have no name?
Java's objects aren't types even though they're mixed up with its type system. Objects are supposed to represent units of computation so anonymous classes aren't absurd.
But the reason why it seems that types without names are absurd is that types are only real for the interpreter or compiler. At runtime they aren't used anymore. So it's absurd that a construct made for humans to understand and describe code starts to become something opaque to human understanding because they're impossible to be named.
