2
Why write a function object somewhere else?
class IsEqualToInt {
int val;
public:
IsEqualToInt( int v ) : val(v) { }
template<typename T> bool operator()( T t ) { return t == val; }
};
int val;
public:
IsEqualToInt( int v ) : val(v) { }
template<typename T> bool operator()( T t ) { return t == val; }
};
find_if(
v.begin(), v.end(), IsEqualToInt(3) ); // code lives elsewhere
find_if(
v.begin(), v.end(), { return _x == 3; } ); // lambda function
find_if(
v.begin(), v.end(), _x == 3 ); // lambda expression
Commonality:
•Boost.Lambda exists
today; language support is a frequently requested extension for
ISO C++0x. No serious
proposal yet, but together concepts + lambdas take STL to next level.
•Directly leveraged in
Concur and Linq. Concur
allows lambda function objects to be active, which is a natural abstraction to spin off arbitrary asynchronous work.
Linq programmers can easily pass around predicates and other code.
Lambda
Functions