CODEWITHSUNDEEP
c++
obamator
obamator

Reputation: 468

Forcing function to be called as assignment operand only

Is it possible to declare a function in such a way that

auto i = foo.GetLock();

works, but

foo.GetLock();

causes a compile error?

My interface has a method that returns RIIA-style lock object and I want to make sure nobody decides just calling GetLock() locks the lock.

It used to be something like this

class CSomethingOrElse : private CLockable
{
    ...
} foo;

CLocker<CSomethingOrElse> lock(foo);

but it's too verbose for my taste and I would really like to make use of auto.

Upvotes: 1

Views: 61

Answers (1)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726809

foo.GetLock(); is an expression statement, so any valid expression can be used in that way. You cannot prohibit that at compile time: the best you can get is a warning.

Assuming that your object releases the lock on destruction, the call that does not store the result in a variable shouldn't be a big problem, because the lock would be acquired and released right away.

Creating a guard object, similar to what you describe in your solution, is the proper way to go. In fact, the Standard Library of C++ does it in a similar way with std::lock_guard.

Upvotes: 1

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