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boost::bind(&print,&std::cout, boost::bind(&vec_type::size,. boost::bind(&map_type::value_type::second,_1))));. There are several options available to use when creating a function object like print_size . reference to a std::ostream , and used that ostream to print the return value of size for the member second on the map_type::value_type argument.. Here's the original print_size again:. class print_size { std::ostream&. map_type;. print_size(std::ostream&. We could remove the state by adding...
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The library addresses a problem that is often encountered when using the Standard Library algorithmsthe need to define many simple function objects just to comply with the requirements of the algorithms. Almost all of the Standard Library. Given that both flexible support for binding arguments and for creating function objects directly from expressions are available in the Boost.Lambda library, it...
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There can be zero or more arguments to the function, some of these can be set directly, some supplied when the function is invoked. With the current version of Boost.Lambda, up to nine arguments are supported (three of which can be applied later through the use of placeholders). To use the binders, you need to include the header "boost/lambda/bind.hpp".. When...
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To create named constants and variables, one simply has to define a variable of the type boost::lambda::constant_type<T>::type and boost::lambda::var_type<T>::type , where T is the type of the wrapped constant or variable. std::cout <<. <<. #include "boost/lambda/lambda.hpp". using boost::lambda::constant;. using boost::lambda::constant_type;. constant_type<char>::type newline(constant('\n'));. constant_type<char>::type space(constant('. boost::lambda::placeholder1_type. vec.push_back(0);. vec.push_back(1);. vec.push_back(2);. vec.push_back(3);. vec.push_back(4);. space <<. vec_.push_back(t);. vec_.clear();. void report() const { using boost::lambda::_1;....
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Transform using std::bind1st and std::plus std::transform(vec.begin(),vec.end(),vec.begin. std::transform(vec.begin(),vec.end(),vec.begin(),_1-=4);. std::for_each(vec.begin(),vec.end(),_1+=10);. std::for_each(vec.begin(),vec.end(),_1-=10);. std::for_each(vec.begin(),vec.end(),_1*=3);. std::for_each(vec.begin(),vec.end(),_1/=2);. std::for_each(vec.begin(),vec.end(),_1%=3);. class search_for_me { std::string a_;. std::string b_;. search_for_me(). search_for_me(const std::string&. a,const std::string&. std::string a() const { return a_;. std::string b() const { return b_;. std::vector<search_for_me>. vec.push_back(search_for_me("apple","banana"));. vec.push_back(search_for_me("orange","mango"));. std::vector<search_for_me>::iterator it=. std::find_if(vec.begin(),vec.end(),???);. if (it!=vec.end()). std::cout <<. it->a() <<. find_if requires an additional predicate function (or function object).. class a_finder {...
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vec.push_back(2);. vec.push_back(1);. add_prev<int>. vec.begin. vec.end. vec.begin(),. std::transform(vec.begin(),vec.end(),vec.begin(),bind(var(ap),_1));. Thus, the program does not compile, and you must explicitly tell bind the return type, like so:. std::transform(vec.begin(),vec.end(),vec.begin. This is a shorthand notation for the general form of explicitly setting the return types for lambda expression, and it's the equivalent of this code.. There, the solution is to add typedef s that state...
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if_then_else_return , which calls the conditional operator. Remember that to use if-constructs, "boost/lambda/if.hpp". For switch , "boost/lambda/switch.hpp". The following examples all assume that the declarations in the namespace boost::lambda have been brought to the current scope through using declarations or a using directive.. (if_then(_1<5,. std::cout <<. The if_then function starts with a condition, followed by a then-part. (if_then(_1<5,std::cout <<. if_then(_1<5,std::cout...
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#include "boost/lambda/lambda.hpp". #include "boost/lambda/casts.hpp". #include "boost/lambda/if.hpp". #include "boost/lambda/bind.hpp". (if_then_else(bind(&String::size,_1)<_2, var(std::cout) <<. "Quite short...\n",. constant("Quite long...\n")))(s,i);. is_it_long(s,4u);. is_it_long(s,4);. #include "boost/lambda/construct.hpp". #include "boost/shared_ptr.hpp". var(std::cout) <<. <<. bind(&map_type::value_type::first,_1) <<. already has a valid pointer.\n"));. "\nHere we go again...\n";. <<
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condition, so we move on to the then-part.. The innermost bind takes care of the default construction of an instance of derived on the heap, and to the result we bind a constructor call to ptr_type (the smart pointer type), which is then assigned (using the usual notation for assignment) to the very first bind. var(std::cout) <<. <<. bind(&map_type::value_type::first,_1) <<....
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In this case, it is created by binding a call to the some_exception constructor, to which we pass the what argument, a string literal.. That's all there is to exception handling in Boost.Lambda. You would otherwise create a simple function object. You want to create standard-conforming function objects on-the-fly. The preceding reasons are just some of the cases where using...
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To start using Boost.Function, include "boost/function.hpp", or any of the numbered versions, ranging from "boost/function/function0.hpp". "boost/function/function10.hpp". When including "boost/function.hpp", the other headers are all included, too.. necessarily at the time when the function is created. When declaring functions, the most important part of the declaration is the function signature. This is where you tell the function about the signature and...
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Fortunately, it is possible to directly call member functions if the class instance is passed to the function . The signature of the function needs to include the type of the class, as well as the signature of the member function. The result is a function object that invokes a member function on the supplied object. std::cout <<. <<. i...
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The power that is wielded with the addition of state to callbacks is tremendous, and is one of the great advantages to using Boost.Function rather than function. Using Boost.Bind with Boost.Function. Things become even more interesting when we combine Boost.Function with a library that supports argument binding. Boost.Bind provides argument binding for free functions, class member functions, and class variables....
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If the function doesn't contain a target, a function or function object, this yields false , which means that we cannot invoke it. To create the concrete commands, we use Boost.Bind to create function objects that, when invoked through the function call operator, calls the correct member function of tape_recorder. In other words, the following code snippet creates a function...
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This is true regardless of the actual design that is used to implement a library with this kind of functionality. It also works with function objects returned from binder libraries, such as Boost.Bind and Boost.Lambda. Our class is a lot more simplistic than the ones found in Boost.Function, but it should be sufficiently detailed to see the problems and the...
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compatible with the function signature of the signal. both are then connected to the signal that we create.. std::cout <<. boost::signal<void ()>. sig.connect(&my_first_slot);. sig.connect(my_second_slot());. "Emitting a signal...\n";. For one, we call connect with the address of the free function, my_first_slot. However, the order of the last two lines is unspecified because slots belonging to the same group are invoked in...
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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. The first argument to the signal class template is the signature for invoking the signal, and this signature is also used for the connected...
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"parking_lot_guard::leave(". Still, these classes are remarkably simple for what they're about to do.) To make the shared_ptr s for the alarm and the car identifiers behave correctly, we implement the default constructor, where the signal and the vector are properly allocated. The function connect_to_alarm forwards to call to the contained signal 's connect . The function call operator tests the...
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std::cout <<. With the preceding code, there is no way that the code will ever know that one of the tests has failed. boost::last_value, and it simply returns the value of the last slot call, which is the call to step2 . We need a Combiner that stops processing when a slot returns false , and propagates that value back...
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boost::signals::scoped_connection s=sig.connect(slot());. However, you'll find even more power when you combine Boost.Signals with Boost.Bind and Boost.Lambda.. (These examples are rather contrived, but the expressions could perform any kind of useful computation.) The last two slots created in the example will do exactly what double_slot and plus_slot did in an example earlier in the chapter. sig.connect(var(std::cout). sig.connect(. sig2.connect(0,_1*=2. Thus, a configurable...