Just like any other function call, there's nothing implicit or hidden.
The implicit part is the question of whether an operator is built-in or overloaded. In C, every operator is built-in, so you can look at a block of code and see that there are NO function calls in it. With something like C++, you must treat every operator like a function call.
With C, if I write:
a += b;
I can be VERY confident that this line of code will execute in constant time. With C++ (or other operator-overloaded language), I cannot. I need to know what the types of a and b are, and I need to go look up the += operator to see what it does for these types (and this is not one universal place, it's specific to the type).
Furthermore, this may be the last line within a particular scope. With C I know that nothing else will happen, and that the control flow depends only on the surrounding scope. With C++, I don't know this! There may have been many objects created within this scope and now their destructors are firing and potentially very large trees of objects are being cleaned up and deallocated, and even slow IO operations running.
> With C++ (or other operator-overloaded language), I cannot
All programming requires people to follow reasonable conventions. In C++ if you make a dereference operator with non-constant time, or an equality operator which doesn't follow equality semantics, the programmer messed up. It's like giving a function a misleading name, like `doThis()` and it doesn't.
Note that Java is filled with these kinds of conventions, such as overloading `equals`. How can you be certain it actually obeys equality semantics? You have to trust the programmer.
The implicit part is the question of whether an operator is built-in or overloaded. In C, every operator is built-in, so you can look at a block of code and see that there are NO function calls in it. With something like C++, you must treat every operator like a function call.
With C, if I write:
I can be VERY confident that this line of code will execute in constant time. With C++ (or other operator-overloaded language), I cannot. I need to know what the types of a and b are, and I need to go look up the += operator to see what it does for these types (and this is not one universal place, it's specific to the type).Furthermore, this may be the last line within a particular scope. With C I know that nothing else will happen, and that the control flow depends only on the surrounding scope. With C++, I don't know this! There may have been many objects created within this scope and now their destructors are firing and potentially very large trees of objects are being cleaned up and deallocated, and even slow IO operations running.