A Summary: Expression-Assignments. (Very Long)

[Evan Simpson]

Michael P. Reilly wrote:
[snip]
> Since assignment works on references to variables, this can lead to some
> complications.  Also, there are a good number of ambiguities that result
> from working with overloaded objects.
[snip]
>  x = 1    # simple assignment
>  x += 2   # simple: x = ( x + 2 )
>  x += B() # should x now result in an integer or an instance of B?


Some better examples of ambiguity:

(x, y, z) += 1
# (x, y, z) = (x, y, z) + 1 is meaningless.  How about (x, y, z) = (x + 1, y
+ 1, z + 1)?
(x, y, z) += (1, 2, 3)
# oops.  Here people might expect (x, y, z) = (x+1, y+2, z+3) instead.
(spam, eggs) += x += "huh?"
# What could this mean?  It looks funky.
x += y *= z <<= 2
# Aaeeiii!

Suppose we cut down "+=" style statements by forbidding these cases.  Only
allow simple LHS += RHS constructions.  Now we have a heap of statements
roughly similar to "=", but obeying different rules.  Ugh.

Of course, we now have a way to make "setadd(x, 1)" mean "x = x + 1".

bytecodehacks-to-the-rescue-ly y'rs
Evan Simpson