digitalmars.D - const/invariant/pure/mutable living happily together
- Steven Schveighoffer (40/40) Sep 12 2007 In the "invariant const sucks" thread, there has been a lot of activity,...
In the "invariant const sucks" thread, there has been a lot of activity, and so I wanted to post my ideas on this outside the thread so it doesn't get lost in the noise. Basically, I think const/invariant/pure/mutable can all be used at the same time and everyone can get what they want. BEGIN DEFINITION const and invariant work as Walter described in his original post "const sucks", with the added feature that a class method can be declared invariant if it does not modify any members of a class except members declared as mutable. mutable is a new keyword that can be used only on a class member. A class member defined as mutable can be changed by a const function. Now, I have 2 different possible definitions of pure. The first is if the compiler is assuming the responsibility of thread concurrency. That is, the compiler assumes that if it has 2 pure function calls in sequence, it can call them simultaneously on parallel processors without worrying that another thread or signal will modify the data. Here is that definition: A function can be declared pure with the pure keyword. A pure function cannot modify any data that is not scoped in the function. A pure function can only call other pure functions. A pure function can only access data outside its scope that is declared invariant. The second definition is if the compiler does not assume the responsibility of thread concurrency: A function can be declared pure with the pure keyword. A pure function cannot modify any data that is not scoped in the function. A pure function can only call other pure functions. A pure function can read any data outside its scope that is declared const. END DEFINITION Can functional programming not work with at least one of the 2 definitions? If not, why? I have no real experience with functional programming, so I may have that stuff wrong. And PLEASE PLEASE if you want to show that something is wrong with my proposal, present a real example. I have a hard time accepting arguments like "that won't work because functional programming requires no mutable data." It's like saying "because I said so" :) And I totally don't mind if I'm wrong. I would LOVE to be proven wrong so that I can stop thinking about this issue. I just can't understand why this doesn't work. -Steve
Sep 12 2007
"Steven Schveighoffer" wroteIn the "invariant const sucks" thread,Should have read "transitive const sucks", sorry -Steve
Sep 12 2007
If you're thinking of responding to this thread, don't. I no longer think this is correct. Look at my 'logical const is a subset of transitive const' thread instead. -Steve
Sep 14 2007