Menu
I remember that when using Boost.Spirit and for the std::function addition to C++0x, you specify the function type by using a syntax that doesn't use pointers, like in defining std::function<bool(int)> fn, whereas you would cast a pointer like (bool(*)(int))fn.
Can anyone tell me the name of this new syntax or any references on this, or how to use it? It seems like a polymorphic function type syntax that applies for functors as well, but I don't really know how to use it.
915
A function template starts with the keyword template followed by template parameter(s) inside <> which is followed by the function definition. In the above code, T is a template argument that accepts different data types ( int , float , etc.), and typename is a keyword.
What is the correct syntax of defining function template/template functions? Explanation: Starts with keyword template and then <class VAR>, then use VAR as type anywhere in the function below. 7.
1. What is the syntax of class template? Explanation: Syntax involves template keyword followed by list of parameters in angular brackets and then class declaration.
A template is a simple yet very powerful tool in C++. The simple idea is to pass data type as a parameter so that we don't need to write the same code for different data types. For example, a software company may need to sort() for different data types.
bool(int) is the type of the function; bool(*)(int) is the type of the function pointer. In other words, if you define
typedef bool(BF)(int);
typedef bool(pBF*)(int);
then BF* is the same as pBF.
The std::function template captures the return and argument types via (variadic) templates:
template <typename R, typename ...Args> struct function
{
function(R(&f)(Args...)); // conceptually
}
It is not new sintax, although old compilers did sometimes reject it. It is simply the type of a function versus the type of a function pointer, similar to the type of an arrays versus the pointer to an array.
The facts that there are no function l-values and that function r-values decay quickly to pointer-to-functions make them mostly useless. Except in the case of templates, of course.
32
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
