On Mon, Jan 23, 2017 at 12:49:19AM -0200, Soni L. wrote: [...]
You seem to be thinking of "immutable object builder". Not "the builder itself is immutable and operations on it create new builders".
Why would you make a builder class immutable? That's not a rhetorical question -- I'm genuinely surprised that you're not only using the builder design pattern (there are usually better solutions in Python) but more so that you're making the builder itself immutable. In any case, it seems that this is such a narrow and unusual use-case that it wouldn't be wise to give it special syntax. Especially when there are other, potentially far more useful, uses for the .= syntax, e.g. Julia's syntactic loop fusion: http://julialang.org/blog/2017/01/moredots -- Steve