TAILIEUCHUNG - HandBooks Professional Java-C-Scrip-SQL part 94

Tham khảo tài liệu 'handbooks professional java-c-scrip-sql part 94', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | function f_ in a Boolean context. If the function doesn t contain a target a function or function object this yields false which means that we cannot invoke it. This is tested in the implementation of execute. Here s a sample program that uses our new class int main tape_recorder tr command play boost bind tape_recorder play tr command stop boost bind tape_recorder stop tr command forward boost bind tape_recorder stop tr command rewind boost bind tape_recorder rewind tr command record Invoked from some GUI control. if Invoked from some scripting client. Some inspired songwriter has passed some lyrics std string s What a beautiful morning. record. set_function boost bind tape_recorder record tr s To create the concrete commands we use to create function objects that when invoked through the function call operator calls the correct member function of tape_recorder. These function objects are self-contained they are nullary function objects meaning that they can be directly invoked without passing any arguments which is what a boost function void expects. In other words the following code snippet creates a function object that invokes the member function play on the instance of tape_recorder that it is configured with. boost bind tape_recorder play tr Normally we wouldn t be able to store the returned function object from the call to bind but because is compatible with any function object this is possible. boost function void f boost bind tape_recorder play tr Notice that the class also supports calling record which takes an argument of type const std string because of the member function set_function. Because the function object must be nullary we need to bind the context so that record still gets its argument. That of course is a job for binders. Thus before calling record we create a function object that contains the string to be recorded. std string s-What a beautiful morning. record.

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• Java C Scrip SQL
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