In object-oriented languages, function object (also known as functor) is a feature that allows objects to be used like if they were ordinary functions.
Questions tagged [function-object]
168 questions
1061
votes
14 answers
What are C++ functors and their uses?
I keep hearing a lot about functors in C++. Can someone give me an overview as to what they are and in what cases they would be useful?
Konrad
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138
votes
9 answers
Build a function object with properties in TypeScript
I want to create a function object, which also has some properties held on it. For example in JavaScript I would do:
var f = function() { }
f.someValue = 3;
Now in TypeScript I can describe the type of this as:
var f: { (): any; someValue: number;…
JL235
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62
votes
3 answers
Are functors actually faster than pointers to functions?
According to Scott Meyers, one area where C++ shines over C is that function objects are faster than function pointers. He says this is because function objects are inlined, which increases speed.
I have two questions about this:
How can we verify…
user7140484
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57
votes
5 answers
How does the template parameter of std::function work? (implementation)
In Bjarne Stroustrup's home page (C++11 FAQ):
struct X { int foo(int); };
std::function f;
f = &X::foo; //pointer to member
X x;
int v = f(&x, 5); //call X::foo() for x with 5
How does it work? How does std::function call a foo…
Sadeq
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40
votes
2 answers
Overloading multiple function objects by reference
In C++17, it is trivial to implement an overload(fs...) function that, given any number of arguments fs... satisfying FunctionObject, returns a new function object that behaves like an overload of fs.... Example:
template
struct…
Vittorio Romeo
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28
votes
7 answers
How can it be useful to overload the "function call" operator?
I recently discovered that in C++ you can overload the "function call" operator, in a strange way in which you have to write two pair of parenthesis to do so:
class A {
int n;
public:
void operator ()() const;
};
And then use it this way:
A…
lurks
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23
votes
4 answers
Overload a lambda function
How to overload a simple local lambda function?
SSE of original problem:
#include
#include
Vinícius
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22
votes
3 answers
why function objects should be pass-by-value
I have just read the classic book "Effective C++, 3rd Edition", and in item 20 the author concludes that built-in types, STL iterators and function object types are more appropriate for pass-by-value. I could well understand the reason for built-in…
JavaBeta
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21
votes
2 answers
What does static_cast mean when it's followed by two pairs of parentheses?
What does this say:
return static_cast(*this)(key);
?
I can't tell whether *this or key is passed to static_cast. I looked around and found this answer, but unlike what I'm stuck on, there's nothing inside the first pair of parentheses.
johnsmith
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20
votes
4 answers
In C++ what does it mean for a compiler to "inline" a function object?
In the wikipedia article about function objects it says such objects have performance advantages when used with for_each because the compiler can "inline" them.
I'm a bit foggy on exactly what this means in this context... or any context I'm…
Monte Hurd
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18
votes
1 answer
Call operator with auto return type being chosen instead of constructor when using std::function
The following snippet:
#include
struct X {
X(std::function fn); // (1)
X(double, double); // (2)
template
auto operator()(T const& t) const { // (3)
return t.foo();
…
Holt
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18
votes
3 answers
Serializing function objects
Is it possible to serialize and deserialize a std::function, a function object, or a closure in general in C++? How? Does C++11 facilitate this? Is there any library support available for such a task (e.g., in Boost)?
For example, suppose a C++…
shaniaki
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14
votes
3 answers
javascript class inherit from Function class
I like that in javascript, I can create a function, and then add further methods and attributes to that function
myInstance = function() {return 5}
myInstance.attr = 10
I would like to create a class to generate these objects. I assume I have to…
dgreisen
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14
votes
3 answers
Detailed difference between functor's call and function call?
The key reason this works is that for_each () doesn’t actually assume
its third argument to be a function.
It simply assumes that its third
argument is something that can be
called with an appropriate argument. A
suitably defined object…
Ramadheer Singh
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12
votes
3 answers
Creating a function object from a string
Question: Is there a way to make a function object in python using strings?
Info: I'm working on a project which I store data in a sqlite3 server backend. nothing to crazy about that. a DAL class is very commonly done through code generation…
Narcolapser
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