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Programming-Idioms

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  • Pascal

Idiom #271 Test for type extension

If a variable x passed to procedure tst is of type foo, print "Same type." If it is of a type that extends foo, print "Extends type." If it is neither, print "Not related."

uses classes;
procedure tst(x: tobject);
begin
  if x.ClassType = foo then
    writeln('Same type')
  else if x is foo then
    writeln('Extends type')
  else
    writeln('Not related');
end; 

The concept of "extending" only applies to classes.

"x is foo" is shorthand for x.InheritsFrom(foo)
#include <iostream>
#include <type_traits>
template<typename T>
void tst(T)
{
    using namespace std;

    // Strip away any references and pointer
    typedef remove_const<remove_pointer<decay<T>::type>::type>::type D;

    if(is_same<D, foo>::value)
    {
        cout << "same type" << endl;
    }
    else if(is_base_of<foo, D>::value)
    {
        cout << "extends type" << endl;
    }
    else
    {
        cout << "not related" << endl;
    }
}

New implementation...
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tkoenig