Monday, February 20, 2012

All(?) OO methods are "static" under the hood

C++ supports "free functions", static method and non-static method. 
- Static method are very similar to free functions. (Difference? Perhaps inheritance and access modifiers.)
- Non-static methods are implemented as free functions accepting "this" as first argument.

C++ is largely based on classic-C. Basically everything translates to classic-C code, which uses free functions only.

Once we understand the c++ world, we can look at java and c# -- Essentially same as c++.

Looking deeper, any method, function or subroutine consists of a sequence of instruction -- a "code object" if you like. This object is essentially singleton because there's no reason to duplicate this object or pass it by value. This object has an address in memory. You get that address in C by taking the address of a function -- so-called function pointers.

In a multi-threaded environment, this code object is kind of singleton and stateless (if you know what I mean!). Think of Math.abs(). The code object itself is never thread-unsafe, but invoking it as a non-static method often is. Indeed, Invoking it as a free function can also be thread-unsafe if the function uses a stateful object. Example -- localtime().

Non-static method has to be implemented based on this code object.

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