TAILIEUCHUNG - HandBooks Professional Java-C-Scrip-SQL part 97

Tham khảo tài liệu 'handbooks professional java-c-scrip-sql part 97', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | that the guard detected a problem can be insufficient a slot may need to know the current temperature. Although both the guard the signal and the slot could access the temperature from a common sensor it may be simplest to have the guard pass the current temperature to the slot when invoking it. As another example consider when slots are connected to several signals The slots will most likely need to know which signal invoked it. There are myriad use cases that require passing some information from signal to slot. The arguments that slots expect are part of a signal s declaration. The first argument to the signal class template is the signature for invoking the signal and this signature is also used for the connected slots when the signal calls them. If we want the argument to be modifiable we make sure that it is passed by non-const reference or pass a pointer else we can pass it by value or reference to const. Note that besides the obvious difference that the original argument is either modifiable or not this also has implications for the types of acceptable arguments to the signal itself and to the slot typeswhen the signal expects an argument by value or as reference to const types that are implicitly convertible to the argument s type can be used to emit a signal. Likewise for slotsif the slot accepts its arguments by value or reference to const this means that implicit conversion to that type from the actual argument type of the signal is allowed. We ll see more of this soon as we consider how to properly pass arguments when signaling. Consider an automatic parking lot guard which receives notifications as soon as a car enters or leaves the parking lot. It needs to know something unique about the carfor example the car s registration number so it can track the coming and going of each. That would also permit the system to know just how ridiculous a sum to charge the owner according to the elapsed time. The guard should also have a signal of its own to be able

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