Is this claim correct: "Anywhere you pass in a function, you can pass in a functor"?

meili100 · 11-21-2007, 06:19 PM

Is this claim correct: "Anywhere you pass in a function, you can pass in a functor"?

for example:

Code:

bool cmp_function(int a, int b){
return a<b;
}

struct cmp_functor{
bool operator()(int a, int b){
return a<b;
}
};

std::sort(vec.begin(), vec.end(), cmp_function);
std::sort(vec.begin(), vec.end(), cmp_functor);

Sebastiani · 11-21-2007, 06:48 PM

no, that is incorrect. but you can often structure your code in a way that allows either to be used. for example:

Code:

template <typename Function>
void
foo(Function callback, int data)
{
	callback(data);
}

void
bar(int)
{	}

struct baz
{
	void
	operator () (int)
	{	}
};

foo(bar, 1);
foo(baz(), 1);

meili100 · 11-21-2007, 07:15 PM

Thank you, I am curious why "baz()" should carry "()". Isn't "baz" enough?

Also, in your example, what would the 2 signatures be if the foo only accepts function or funcotr?

whiteflags · 11-22-2007, 12:58 AM

> I am curious why "baz()" should carry "()". Isn't "baz" enough?
Because baz is an object that needs to be instantiated, just like other classes or structs in C++.

> what would the 2 signatures be if the foo only accepts function or funcotr?
The simplest of the possibilities is probably

void foo( void (*callback )( int ), int data );
void foo( baz callback, int data );

11-21-2007, 06:19 PM	#1
meili100 Registered User Join Date: Apr 2007 Posts: 282	Is this claim correct: "Anywhere you pass in a function, you can pass in a functor"? Is this claim correct: "Anywhere you pass in a function, you can pass in a functor"? for example: Code: bool cmp_function(int a, int b){ return a<b; } struct cmp_functor{ bool operator()(int a, int b){ return a<b; } }; std::sort(vec.begin(), vec.end(), cmp_function); std::sort(vec.begin(), vec.end(), cmp_functor);
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11-21-2007, 06:48 PM	#2
Sebastiani Guest Join Date: Aug 2001 Posts: 5,034	no, that is incorrect. but you can often structure your code in a way that allows either to be used. for example: Code: template <typename Function> void foo(Function callback, int data) { callback(data); } void bar(int) { } struct baz { void operator () (int) { } }; foo(bar, 1); foo(baz(), 1);
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11-21-2007, 07:15 PM	#3
meili100 Registered User Join Date: Apr 2007 Posts: 282	Thank you, I am curious why "baz()" should carry "()". Isn't "baz" enough? Also, in your example, what would the 2 signatures be if the foo only accepts function or funcotr? Last edited by meili100; 11-21-2007 at 07:21 PM.
meili100 is offline

11-22-2007, 12:58 AM	#4
whiteflags MENTAL DETECTOR Join Date: Apr 2006 Location: United States Posts: 3,295	> I am curious why "baz()" should carry "()". Isn't "baz" enough? Because baz is an object that needs to be instantiated, just like other classes or structs in C++. > what would the 2 signatures be if the foo only accepts function or funcotr? The simplest of the possibilities is probably void foo( void (*callback )( int ), int data ); void foo( baz callback, int data );
whiteflags is offline

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