Calling Syntax (no, not UFCS)

[SirNickolas via Digitalmars-d-learn]

Hello! I'm new in D and it is amazing!

Can you tell me please if it is discouraged or deprecated to call 
a function by just putting its name, without brackets? It's quite 
unusual for me (used C++ and Python before), but I can see this 
practice even in the official Phobos documentation:

```
foreach (result; [ 1, 2, 3, 4 ].map!("a + a", "a * a"))
     ...
```

The code `.map!("a + a", "a * a")()` also compiles and works as 
expected, of course.