On 23/01/17 02:56 PM, Gerald Britton wrote:
On Jan 23, 2017 11:07 AM, "Soni L." <fakedme...@gmail.com
<mailto:fakedme%2...@gmail.com>> wrote:
On 23/01/17 01:52 PM, Gerald Britton wrote:
[snip]
>I propose `x .= y` -> `x = x . y`, for any `y`.
[snip]
I think you mean "any y that is a member of x"
Since it desugars into `x = x.y`, you can literally use anything
for `y`.
x .= __call__().whatever().unwrap() * 3
is equivalent to
x = x.__call__().whatever().unwrap() * 3
and
x .= 1
is equivalent to
x = x.1
which is equivalent to
SyntaxError: invalid syntax
Also, note that this syntax means that x will be rebound to
the result of calling x.y, whatever that is (frequently,
None, for mutating methods)
In general, you can't count on methods to return references
to their instances, even though it's handy for fluent coding,
so this side effect may be unexpected to some
This is why it's for use with **immutable** objects.
That's a problem with your original example:
>long_name = mkbuilder()
>long_name = long_name.seta(a)
>long_name = long_name.setb(b)
>y = long_name.build()
What do the methods seta and setb return? If they don't
return "self" you've got a problem. I think.
They don't return self. Ever. The value bound to long_name is
immutable, like an integer. They return a new instance.
Then long_name isn't immutable. It changes with every line. That can
lead to nasty bugs if you count on its immutability.
Easy to see. Just print long_name after each call.
You're mixing up value immutability with name immutability. The name
isn't immutable, but:
long_name = mkbuilder()
x = long_name
long_name .= seta("a")
y = long_name
long_name .= setb("b")
z = long_name
print(x) # a = None, b = None
print(y) # a = "a", b = None
print(z) # a = "a", b = "b"
print(x is y) # False
print(x is z) # False
print(y is z) # False
print(long_name is z) # True
See also:
long_name = 1
x = long_name
long_name += 1
y = long_name
long_name += 1
z = long_name
print(x) # 1
print(y) # 2
print(z) # 3
print(x is y) # False
print(x is z) # False
print(y is z) # False
print(long_name is z) # True
FWIW why can't you just write:
x.y
or for your example:
long_name.seta(a)
?
See the IRC bot builder example, it should be more clear. (It's
about forking the builder.)
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