Two definitions of Delphi function pointers (object methods exist with a hidden argument self, so they cannot be assigned to each other)

The following two definitions are often seen in Delphi

Type

Tmouseproc = procedure (X,y:integer);

Tmouseevent = procedure (X,y:integer) of Object;

They look the same, but the actual meaning is different,

Tmouseproc is only a single function pointer type;

Tmouseevent is a function pointer to an object, which is the function/method of an Object/class

The difference is that the class method has a hidden parameter, self, which means that the two parameters are different, so they cannot be converted to each other

This is why Delphi can be assigned such button1.onclick:=button2.onclick;

But can not be so assigned to the value of Button1.onclick=buttonclick; (ButtonClick is the local function, Button2.onclick is the class method)!

http://blog.csdn.net/procedure1984/article/details/3897155

Two definitions of Delphi function pointers (object methods exist with a hidden argument self, so they cannot be assigned to each other)