[Python-ideas] "Immutable Builder" Pattern and Operator

[Soni L.]

On 22/01/17 10:03 PM, Wes Turner wrote:
>
>
> On Sunday, January 22, 2017, Wes Turner <wes.turner at gmail.com 
> <mailto:wes.turner at gmail.com>> wrote:
>
>     Have you looked at pyrsistent for
>     immutable/functional/persistent/copy-on-write data structures in
>     Python?
>
>     https://github.com/tobgu/pyrsistent/
>     <https://github.com/tobgu/pyrsistent/>
>
>     (freeze() / thaw())
>
>     ... e.g. List and Dict NamedTuple values are not immutable
>     (because append() and update() still work)
>
>
> fn.py also has immutables:
> https://github.com/kachayev/fn.py/blob/master/README.rst#persistent-data-structures

You seem to be thinking of "immutable object builder". Not "the builder 
itself is immutable and operations on it create new builders".

>
>     On Sunday, January 22, 2017, Soni L. <fakedme+py at gmail.com
>     <javascript:_e(%7B%7D,'cvml','fakedme%2Bpy at gmail.com');>> wrote:
>
>         I've been thinking of an Immutable Builder pattern and an
>         operator to go with it. Since the builder would be immutable,
>         this wouldn't work:
>
>         long_name = mkbuilder()
>         long_name.seta(a)
>         long_name.setb(b)
>         y = long_name.build()
>
>         Instead, you'd need something more like this:
>
>         long_name = mkbuilder()
>         long_name = long_name.seta(a)
>         long_name = long_name.setb(b)
>         y = long_name.build()
>
>         Or we could add an operator to simplify it:
>
>         long_name = mkbuilder()
>         long_name .= seta(a)
>         long_name .= setb(b)
>         y = long_name.build()
>
>         (Yes, I'm aware you can x = mkbuilder().seta(a).setb(b), then
>         y = x.build(). But that doesn't work if you wanna "fork" the
>         builder. Some builders, like a builder for network connections
>         of some sort, would work best if they were immutable/forkable.)
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