pass-by-reference

问题 How would one write PHP code to call all "Callables" with __invoke() ? The desire here is pass by reference, which is deprecated with call_user_func[_array]() . I did see that there is a package out there, TRex\Reflection\CallableReflection , but this seems to utilize call_user_func() in the background, and would suffer the same issue. <?php function passthrough_invoke(callable $callback) { return $callback->__invoke(); } function passthrough_user(callable $callback) { return call_user_func(

问题 This question already has answers here : Is it counter-productive to pass primitive types by reference? [duplicate] (7 answers) Closed 4 years ago . When I pass primitives like int and double to functions , is it better to pass them by const reference , or by value (assuming that I don't change the variable's value) ? int getValueFromArray(int index) { // return the value from the array } int getValueFromArray(const int& index) { // return the value from the array } Thanks 回答1: For primitive

问题 This question already has answers here : Is it counter-productive to pass primitive types by reference? [duplicate] (7 answers) Closed 4 years ago . When I pass primitives like int and double to functions , is it better to pass them by const reference , or by value (assuming that I don't change the variable's value) ? int getValueFromArray(int index) { // return the value from the array } int getValueFromArray(const int& index) { // return the value from the array } Thanks 回答1: For primitive

问题 I have a array like this: users = [{id:1, name:'name1'},{id:2, name:'name2'}] How could I get a reference to the item {id:2, name:'name2'}, so I can change it is name property, like: user = get_item(users, 'id', 2); user.name = "user2 name changed"; console.log(users) will have the result: [{id:1, name:'name1'},{id:2, name:'user2 name changed'}] I tried to use Array.filter() function, but it returns a new array instead of a reference to the original array. which I can not use to mutate the

问题 Should a C++ (implicit or explicit) value constructor accept its parameter(s) by value or reference-to-const, when it needs to store a copy of the argument(s) in its object either way? Here is the shortest example I can think of: struct foo { bar _b; foo(bar [const&] b) // pass by value or reference-to-const? : _b(b) { } }; The idea here is that I want to minimize the calls to bar's copy constructor when a foo object is created, in any of the various ways in which a foo object might get

问题 While testing my code, I found out the following: If I assign a data.table DT1 to DT and change DT afterwards, DT1 changes with it. So DT and DT1 seem to be internally linked. Is this intended behavior? Although I'm not a programming expert, this looks wrong to me, and testing it with simple R variables or a data.frame , I couldn't reproduce the behavior. What's happening here? DF <- data.frame(ID=letters[1:5], value=1:5) DF1 <- DF all.equal(DF1, DF) [1] TRUE DF[1, "value"] <- DF[1, "value"]

问题 How do I modify an argument being passed to a function in R? In C++ this would be pass by reference. g=4 abc <- function(x) {x<-5} abc(g) I would like g to be set to 5. 回答1: There are ways as @Dason showed, but really - you shouldn't ! The whole paradigm of R is to "pass by value". @Rory just posted the normal way to handle it - just return the modified value... Environments are typically the only objects that can be passed by reference in R. But lately new objects called reference classes

问题 Does declaring something like the following void foo(int x) { std::cout << "foo(int)" << std::endl; } void foo(const int &x) { std::cout << "foo(const int &)" << std::endl; } ever make sense? How would the caller be able to differentiate between them? I've tried foo(9); // Compiler complains ambiguous call. int x = 9; foo(x); // Also ambiguous. const int &y = x; foo(y); // Also ambiguous. 回答1: The intent seems to be to differenciate between invocations with temporaries (i.e. 9 ) and 'regular'

问题 In PHP, function parameters can be passed by reference by prepending an ampersand to the parameter in the function declaration, like so: function foo(&$bar) { // ... } Now, I am aware that this is not designed to improve performance, but to allow functions to change variables that are normally out of their scope. Instead, PHP seems to use Copy On Write to avoid copying objects (and maybe also arrays) until they are changed. So, for functions that do not change their parameters, the effect

问题 In PHP, function parameters can be passed by reference by prepending an ampersand to the parameter in the function declaration, like so: function foo(&$bar) { // ... } Now, I am aware that this is not designed to improve performance, but to allow functions to change variables that are normally out of their scope. Instead, PHP seems to use Copy On Write to avoid copying objects (and maybe also arrays) until they are changed. So, for functions that do not change their parameters, the effect