Re: [Xotcl] constant/immutable property

From: Victor Mayevski <vitick_at_gmail.com>
Date: Tue, 3 Jan 2012 11:47:58 -0800

Thank you Gustaf and Sefan,

Would it be possible to add that functionality into NX core? For example, via:

Obj property {key:constant value}
Obj variable key:constant value

I know I can code it myself but I think programmers would prefer for
it to be a built-in function.

> On Mon, Jan 2, 2012 at 8:28 AM, Stefan Sobernig <stefan.sobernig_at_wu.ac.at> wrote:
> Victor,
>
>
>> Maybe this simple study helps already
>
>
> I just recovered a variation of Gustaf's study which I had used in previous
> projects of mine. The study below differs with respect to enforcing the
> "immutability" (prohibiting vs. preserving state) and adds handling of
> variable unsets. It slightly optimizes over the method dispatch for write
> traces (using ::nsf::set::var), however, it also comes at extra costs
> (doubled variable writes).
>
> It can be easily extended for supporting basic introspection, kinds of
> "/obj/ info immutables" or the like ...
>
> //stefan
>
>
> package req nx
> package req nx::test
> package req nx::trait
>
> ::nx::Class create C {
>  :require trait nx::traits::callback
>  #
>  # Make selected (by default, all currently defined) variables of an
>  # object immutable
>  #
>  :public forward immutable %self traces add
>
>  #
>  # Make selected (by default, all currently defined) variables of an
>  # object mutable (again ...)
>  #
>  :public forward mutable %self traces remove
>
>  :protected method traces {op args} {
>    foreach varName [expr {[llength $args] ? $args : [:info vars]}] {
>      set writeCmdPrefix [list ::nsf::var::set [self] $varName [set
> :$varName]]
>      set unsetCmdPrefix "$writeCmdPrefix; [:callback immutable $varName]"
>      ::trace $op variable :$varName write "$writeCmdPrefix;#"
>      ::trace $op variable :$varName unset "$unsetCmdPrefix;#"
>
>    }
>  }
>  :create c1 {
>    set :x 1
>    set :y 2
>  }
> }
>
> #
> # c1 is mutable ...
>
> #
> ? {c1 eval {set :x}} 1
> ? {c1 eval {set :y}} 2
> ? {c1 eval {set :x 5}} 5
> ? {c1 eval {set :x}} 5
> ? {c1 eval {unset :y; set :y}} {can't read ":y": no such variable}
> ? {c1 eval {set :y 4}} 4
>
> ? {c1 eval {set :z 3}} 3
>
> #
> # c1 becomes immutable ...
>
> #
> c1 immutable
>
> ? {c1 eval {set :x}} 5
> ? {c1 eval {set :y}} 4
> ? {c1 eval {set :x 1}} 5
> ? {c1 eval {set :x}} 5
> ? {c1 eval {unset :y; set :y}} 4
> #
> # Subsequent unsets are handled ...
> #
> ? {c1 eval {unset :y; set :y}} 4
> ? {c1 eval {set :y 2}} 4
>
> ? {c1 eval {set :z 3}} 3
>
> #
> # c1 becomes mutable (again ...)
> #
>
> c1 mutable
>
>
> ? {c1 eval {set :x}} 5
> ? {c1 eval {set :y}} 4
> ? {c1 eval {set :x 1}} 1
>
> ? {c1 eval {set :x}} 1
> ? {c1 eval {unset :y; set :y}} {can't read ":y": no such variable}
> ? {c1 eval {set :y 2}} 2
> ? {c1 eval {set :z 3}} 3
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