On Thu, 07 Oct 2010 10:43:18 +0400, Russel Winder <rus...@russel.org.uk>
wrote:
On Wed, 2010-10-06 at 23:08 -0700, Walter Bright wrote:
If expr represents a tuple, we (Andrei and I) were thinking about the
syntax:
auto (a, b, c, d) = expr;
being equivalent to:
auto t = expr; auto a = t[0]; auto b = t[1]; auto c = t[2 .. $];
You can also do this with arrays, such that:
float[3] xyz;
auto (x, y, z) = xyz;
The Lithpers among you will notice that this essentially provides a
handy
car,cdr shortcut for tuples and arrays:
auto (car, cdr) = expr;
Python may be the best base to compare things to as tuple assignment has
been in there for years.
Pythons choice is not a car/cdr approach but an exact match approach.
so if t represents a tuple datum or a function returning a tuple:
x = t
then x is a tuple -- remembering that variables are all just references
to objects implemented via keys in a dictionary, and:
a , b , c = t
or
( a , b , c ) = t
is tuple assignment where now t is required to be a tuple of length 3.
cf.
|> python
Python 2.6.5 (r265:79063, Apr 16 2010, 13:57:41)
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more
information.
>>> t = ( 1 , 'fred' , 2.0 )
>>> x = t
>>> print x
(1, 'fred', 2.0)
>>> a , b , c = t
>>> print a , b , c
1 fred 2.0
>>> a , b = t
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: too many values to unpack
>>> a , b , c , d = t
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: need more than 3 values to unpack
>>>
That's because Python is not a strictly typed language. With proper type
propagation compiler helps you writing code the way in meant to be. E.g.
the following:
(a, b, c, d) = ('tuple', 'of', 'three')
could be statically disabled, but there is nothing wrong with allowing it
either: d would be just a no-op, you will know it for sure the moment you
try using it.
