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

[Soni L.]

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.)