Hi Andrew, I had written: >Which part surprises you? to which you replied > >That Interface/Test returns the value of 't! In C++, this wouldn't >work, as the function 'Test_Implementation wouldn't be able to find 't >in 'Interface. It's disturbing to me as a C++ programmer, but viewing >it as a novice might, it seems perfectly correct that the copied >function "knows" where t is. A) While REBOL was not fashioned in the likeness of C++, what is happening here is not unusual from a C++ point of view. After all, if you have a class in C++ that contains a private variable and a public function, and the public function manipulates the private variable, then you can reference and modify the value of the private variable by using the public function of the class. That is trivial. B) What is happening here is similar. 1. Test_Implementation is a word that refences the value returned by make function! [] [t] in Implementation's context. 2. "in Implementation 'Test_Implementation" returns the word Test_Implementation that is bound in Implementation's context. 3. the function "get" in the expresssion "get in Implementation Test_Implementation" retrieves the value of Test_Implementation in Implementation's context, which is the result of make function! [] [t] 4. The assignment "Test:" in "Test: get in Implementation Test_Implementation": Test is assigned as a reference to the function identified in the previous step. Since 't is defined in Implementation's context and get retrieved the function defined in Implementation's context, Interface's 'Test has now become a reference to a function (not only the specification, the function itself) which is implemented in and therefore has access to words defined in Implementation's context. 5. When you evaluate Interface/Test, a) Test is dereferenced and evaluates to the function [] [t] defined in Implementation's context. b) The function [] [t] is evaluated in Implementation's context. c) t is dereferenced in Implementation's context. d) t's values is returned by the function, which was referenced by the word Test. In summary, Interface's word 'Test does not know of 't. 'Test only knows a function. That function is implemented in Implementation's context and therefore has access to words defined in Implementation's context, one of which happens to be 't. Compare to C++: Define Implementation as a class. Define t as a private variable. Define Test_Implementation as a public function that returns whatever t happens to contain. Define Interface as another class. Define Test as a public pointer to a function and assign it to point at the public function Test_Implementation in Implementation. Then executing Test will return the value contained in t. Hope this helps, Elan
