我无法理解Webkit中的deleteOwnedPtr函数

Question

In found this function in Webkit

template<typename T> inline void deleteOwnedPtr(T* ptr)
{
    typedef char known[sizeof(T) ? 1 : -1];
    if(sizeof(known))
        delete ptr;
}

Why they don't use

if (sizeof(T))
    delete ptr;

What does it mean

char known[-1];

Answer 1

found the explanation in the webkit-dev mailing list. It raises compiler errors if someone is trying to delete incomplete types.

https://lists.webkit.org/pipermail/webkit-dev/2010-November/015051.html

If we delete a pointer and the object has incomplete type, we get undefined behavior. Instead this code causes compilation to fail if the object has incomplete type. The use of a negative number for the size of an array is a way to guarantee we get a compilation error.