The intent seems to be to differenciate between invocations with temporaries (i.e. 9) and ‘regular’ argument passing. The first case may allow the function implementation to employ optimizations since it is clear that the arguments will be disposed afterwards (which is absolutely senseless for integer literals, but may make sense for user-defined objects). However, the … Read more
There is no pythonic way of doing this. Python provides very few facilities for enforcing things such as private or read-only data. The pythonic philosophy is that “we’re all consenting adults”: in this case this means that “the function shouldn’t change the data” is part of the spec but not enforced in the code. If … Read more
Expensive-to-move types are rare in modern C++ usage. If you are concerned about the cost of the move, write both overloads: void set_a(const A& a) { _a = a; } void set_a(A&& a) { _a = std::move(a); } or a perfect-forwarding setter: template <typename T> void set_a(T&& a) { _a = std::forward<T>(a); } that will … Read more
The short answer is, Python always does pass-by-value, but every Python variable is actually a pointer to some object, so sometimes it looks like pass-by-reference. In Python every object is either mutable or non-mutable. e.g., lists, dicts, modules and Pandas data frames are mutable, and ints, strings and tuples are non-mutable. Mutable objects can be … Read more
Effbot (aka Fredrik Lundh) has described Python’s variable passing style as call-by-object: http://effbot.org/zone/call-by-object.htm Objects are allocated on the heap and pointers to them can be passed around anywhere. When you make an assignment such as x = 1000, a dictionary entry is created that maps the string “x” in the current namespace to a pointer … Read more
Here is my own contribution for the Java programming language. first some code: public void swap(int x, int y) { int tmp = x; x = y; y = tmp; } calling this method will result in this: int pi = 3; int everything = 42; swap(pi, everything); System.out.println(“pi: ” + pi); System.out.println(“everything: ” + … Read more
Call-by-value The R Language Definition says this (in section 4.3.3 Argument Evaluation) The semantics of invoking a function in R argument are call-by-value. In general, supplied arguments behave as if they are local variables initialized with the value supplied and the name of the corresponding formal argument. Changing the value of a supplied argument within … Read more
It used to be generally recommended best practice1 to use pass by const ref for all types, except for builtin types (char, int, double, etc.), for iterators and for function objects (lambdas, classes deriving from std::*_function). This was especially true before the existence of move semantics. The reason is simple: if you passed by value, … Read more
Re: OP’s Assertion It is universally acknowledged (in C# at least) that when you pass by reference, the method contains a reference to the object being manipulated, whereas when you pass by value, the method copies the value being manipulated … TL;DR There’s more to it than that. Unless you pass variables with the ref … Read more
There are four main cases where you should use pass-by-reference over pass-by-value: If you are calling a function that needs to modify its arguments, use pass-by-reference or pass-by-pointer. Otherwise, you’ll get a copy of the argument. If you’re calling a function that needs to take a large object as a parameter, pass it by const … Read more