lambda

问题 I am trying to figure out if there is a good way to figure out the depth of a particular C# Expression Tree using an iterative approach. We use expressions for some dynamic evaluation and under rare (error) conditions, the system can try to process an Expression Tree that is so large that it blows out the stack. I'm trying to figure out a way to check the depth of the tree prior to allowing the tree to be evaluated. 回答1: The ExpressionVisitor that is included in .Net is recursive, but using a

问题 Is the following C++ code standard compliant? #include <iostream> int main() { [](auto v){ std::cout << v << std::endl; }.operator()<int>(42); } Both clang++ 3.8.0 and g++ 7.2.0 compile this code fine (the compiler flags are -std=c++14 -Wall -Wextra -Werror -pedantic-errors ). 回答1: This is indeed standard compliant. The standard specifies there must be a member operator() , and that it has one template argument for every occurence of auto in its paramater-declaration-clause. There is no

问题 Please consider this example: import java.util.function.Consumer; public class Example { public static void main(String[] args) { Example example = new Example(); example.setConsumer(test -> System.out.println("passed string is " + test)); //uses MyConsumer, why ? example.getConsumer().accept("Test 1"); example.setConsumer((MyConsumer<String>)test -> System.out.println("passed string is " + test)); //uses MyConsumer example.getConsumer().accept("Test 2"); example.setConsumer((Consumer<String>

问题 Please consider this example: import java.util.function.Consumer; public class Example { public static void main(String[] args) { Example example = new Example(); example.setConsumer(test -> System.out.println("passed string is " + test)); //uses MyConsumer, why ? example.getConsumer().accept("Test 1"); example.setConsumer((MyConsumer<String>)test -> System.out.println("passed string is " + test)); //uses MyConsumer example.getConsumer().accept("Test 2"); example.setConsumer((Consumer<String>

问题 I have the Person class: import java.util.*; public class Person { private String name; Map<String,Integer> Skills=new HashMap<>(); // skill name(String) and level(int) public String getName(){ return this.name; } public Map<String,Integer> getSkills(){ return this.Skills; } } And the App class: import java.util.*; import java.util.Map.Entry; import static java.util.stream.Collectors.*; import static java.util.Comparator.*; public class App { private List<Person> people=new ArrayList<>(); //

问题 I have the Person class: import java.util.*; public class Person { private String name; Map<String,Integer> Skills=new HashMap<>(); // skill name(String) and level(int) public String getName(){ return this.name; } public Map<String,Integer> getSkills(){ return this.Skills; } } And the App class: import java.util.*; import java.util.Map.Entry; import static java.util.stream.Collectors.*; import static java.util.Comparator.*; public class App { private List<Person> people=new ArrayList<>(); //

问题 I have a function template, where I want to do perfect forwarding into a lambda that I run on another thread. Here is a minimal test case which you can directly compile: #include <thread> #include <future> #include <utility> #include <iostream> #include <vector> /** * Function template that does perfect forwarding to a lambda inside an * async call (or at least tries to). I want both instantiations of the * function to work (one for lvalue references T&, and rvalue reference T&&). * However,

问题 I have a method that has to remove any element listed in a (small) Set<K> keysToRemove from some (potentially large) Map<K,V> from . But removeAll() doesn't do, as I need to return all keys that were actually removed, since the map might or might not contain keys that require removal. Old-school code is straight forward: public Set<K> removeEntries(Map<K, V> from) { Set<K> fromKeys = from.keySet(); Set<K> removedKeys = new HashSet<>(); for (K keyToRemove : keysToRemove) { if (fromKeys

问题 I have a method that has to remove any element listed in a (small) Set<K> keysToRemove from some (potentially large) Map<K,V> from . But removeAll() doesn't do, as I need to return all keys that were actually removed, since the map might or might not contain keys that require removal. Old-school code is straight forward: public Set<K> removeEntries(Map<K, V> from) { Set<K> fromKeys = from.keySet(); Set<K> removedKeys = new HashSet<>(); for (K keyToRemove : keysToRemove) { if (fromKeys

问题 I have a method that has to remove any element listed in a (small) Set<K> keysToRemove from some (potentially large) Map<K,V> from . But removeAll() doesn't do, as I need to return all keys that were actually removed, since the map might or might not contain keys that require removal. Old-school code is straight forward: public Set<K> removeEntries(Map<K, V> from) { Set<K> fromKeys = from.keySet(); Set<K> removedKeys = new HashSet<>(); for (K keyToRemove : keysToRemove) { if (fromKeys