Does lambda work with only capture clause

Question

I always belived that lambda needs min three things:

[] capture clause
() input param list
{} function body

All of these 3 are needed be it with something inside it or atleast empty

Plz refer code below:
Callable objects for t3 and t4 threads are lambda. One of them works without () i.e. input paramters. Hows it is working ? New addition to c++ and since when ?

https://code.sololearn.com/c62tJ9Eza8A6/?ref=app

Answer 1

The parameter list has always been an optional field for lambda function.

Check cppreference to see different possible syntax of lambda expressions 👇
https://en.cppreference.com/w/cpp/language/lambda