Since C++ knows type, can it infer dot and arrow?

Question

Say I have this code

std::string s = "hello";
std::string* p = &s;
int l = p.length();

Visual Studio and CLion know dot operator is incorrect. Actually when I press key ., both IDE commit the keystroke as ->.

Since C++ is typed, it knows p is a pointer, why doesn't it combine . and -> into one?

Can the syntax be to always use ., if p is pointer, dereference it first, otherwise directly get its member?

***why doesn't it combine . and -> into one?*** Because those are different things. Also for smart pointers you use both. — drescherjm, Apr 23 '19 at 19:34
Redundancy is helpful. Besides, there are smart pointers which need *both* `.` and `->` for different things. — n. m. could be an AI, Apr 23 '19 at 19:35
What is the CLion's and VS hint for `s.begin().` and `s.begin()->`? ;) — R2RT, Apr 23 '19 at 19:35
What happens when you have `T`? You don't know if it is a pointer or not. — NathanOliver, Apr 23 '19 at 19:36
Oups, you got me there. `char` does not have members... `std::vector` would be better thing to explain my point. Anyway, the others have already found better explanation. — R2RT, Apr 23 '19 at 19:41

score 4 · Accepted Answer · answered Apr 23 '19 at 19:36

4

Classes can overload the arrow operator, so there can be objects for which both . and -> are valid. Smart pointers (e.g. std::unique_ptr or std::shared_ptr) and iterators are common examples.

std::unique_ptr<Foo> f;
f.reset(new Foo(42));
f->bar();

Could you design a statically typed language without this distinction? Of course. But C++ has evolved this way, and that's not something you can change today without breaking tons of code.

answered Apr 23 '19 at 19:36

Matteo Italia

123,740
17
206
299

3

If you read the duplicate, it becomes somewhat evident that C++ got the arrow operator purely by luck - we might never have it! Which would mean that overloading it would not be possible either (luckily it would not be introduced specifically for C++), and we wouldn't have smart pointers! – SergeyA Apr 23 '19 at 19:45
@SergeyA they are actually super interesting bits of history (from a time when C was way more similar to a glorified macro assembler) that I didn't know, thank you! – Matteo Italia Apr 23 '19 at 20:10

Since C++ knows type, can it infer dot and arrow?

1 Answers1