Re: [swift-users] Associativity of && and || operator
>
> Remember too that in Swift the *operator* is decoupled from its
> *implementation.* Plenty of people are using && for things like
> constraint or predicate DSLs, where it doesn't short-circuit.
I think I'm convinced. :-)
If you want to use && or || as an accumulator, left-associativity makes
more sense.
```
func || (condition: Condition, val: String) -> Condition {
return condition.addingOr(string: val)
}
condition = condition || ">= 42" || "< 12"
```
Thank you guys!
2017-02-21 3:16 GMT+09:00 Jordan Rose :
> Remember too that in Swift the *operator* is decoupled from its
> *implementation.* Plenty of people are using && for things like
> constraint or predicate DSLs, where it doesn't short-circuit. Of course, a
> non-associative version of && would be quite surprising, so even a custom
> implementation probably shouldn't rely on the left-associativity.
>
> There's one other reason to prefer this way, though, and that's complexity
> in the AST. Recall that the RHS of the standard && (and ||, and ??) is an
> auto-closure—Swift's way to avoid the eager evaluation of the argument.
> Right-associativity would result in heavily-nested autoclosures, and even
> though they'll all be flattened as part of compilation, the AST
> representation still has to model them that way. So purely from a
> compiler-implementation perspective left-associativity has a small edge.
>
> I think you're right that we should have picked right-associativity
> anyway, but at this point I'm not sure it's worth changing it.
>
> Jordan
>
>
> On Feb 17, 2017, at 01:03, Saagar Jha via swift-users <
> swift-users@swift.org> wrote:
>
> Left associativity is most likely just a holdover from the C family–not
> conforming with it would break expectations for programmers coming from
> these languages. And as you mentioned, the compiler will short-circuit the
> condition and stop evaluating as soon as it encounters a false condition,
> so there’s no measurable benefit.
>
> Saagar Jha
>
> On Feb 17, 2017, at 12:54 AM, rintaro ishizaki via swift-users <
> swift-users@swift.org> wrote:
>
> Hello all,
>
> Why the associativity of Logical{Conjunction,Disjunction}Precedence is "
> left"?
>
> If you write: A && B && C, it's grouped as (A && B) && C.
> This means that the && function is *always* called twice: (&&)((&&)(A,
> B), C).
> I feel "right" associativity is more natural: (&&)(A, (&&)(B, C)),
> because the && function is called only once if A is false.
>
> I know that redundant && calls are optimized away in most cases.
> I also know C and C++ standard says: "The && operator groups
> left-to-right", and most programming languages follow that.
>
> But why not "right" associativity?
> What is the difference between logical operators and ?? operator that has
> "right" associativity?
>
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>
>
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>
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Re: [swift-users] Associativity of && and || operator
To me it would be surprising if && grouped differently than * or &; since
it is closely associated with boolean-and, which in turn is the equivalent
operation to multiply in Boolean logic.
On Fri, 17 Feb 2017 at 7:56 pm, rintaro ishizaki via swift-users <
swift-users@swift.org> wrote:
> Hello all,
>
> Why the associativity of Logical{Conjunction,Disjunction}Precedence is "
> left"?
>
> If you write: A && B && C, it's grouped as (A && B) && C.
> This means that the && function is *always* called twice: (&&)((&&)(A,
> B), C).
> I feel "right" associativity is more natural: (&&)(A, (&&)(B, C)),
> because the && function is called only once if A is false.
>
> I know that redundant && calls are optimized away in most cases.
> I also know C and C++ standard says: "The && operator groups
> left-to-right", and most programming languages follow that.
>
> But why not "right" associativity?
> What is the difference between logical operators and ?? operator that has
> "right" associativity?
>
> ___
> swift-users mailing list
> swift-users@swift.org
> https://lists.swift.org/mailman/listinfo/swift-users
>
--
-- Howard.
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Re: [swift-users] Associativity of && and || operator
Remember too that in Swift the operator is decoupled from its implementation.
Plenty of people are using && for things like constraint or predicate DSLs,
where it doesn't short-circuit. Of course, a non-associative version of &&
would be quite surprising, so even a custom implementation probably shouldn't
rely on the left-associativity.
There's one other reason to prefer this way, though, and that's complexity in
the AST. Recall that the RHS of the standard && (and ||, and ??) is an
auto-closure—Swift's way to avoid the eager evaluation of the argument.
Right-associativity would result in heavily-nested autoclosures, and even
though they'll all be flattened as part of compilation, the AST representation
still has to model them that way. So purely from a compiler-implementation
perspective left-associativity has a small edge.
I think you're right that we should have picked right-associativity anyway, but
at this point I'm not sure it's worth changing it.
Jordan
> On Feb 17, 2017, at 01:03, Saagar Jha via swift-users
> wrote:
>
> Left associativity is most likely just a holdover from the C family–not
> conforming with it would break expectations for programmers coming from these
> languages. And as you mentioned, the compiler will short-circuit the
> condition and stop evaluating as soon as it encounters a false condition, so
> there’s no measurable benefit.
>
> Saagar Jha
>
>> On Feb 17, 2017, at 12:54 AM, rintaro ishizaki via swift-users
>> mailto:swift-users@swift.org>> wrote:
>>
>> Hello all,
>>
>> Why the associativity of Logical{Conjunction,Disjunction}Precedence is
>> "left"?
>>
>> If you write: A && B && C, it's grouped as (A && B) && C.
>> This means that the && function is always called twice: (&&)((&&)(A, B), C).
>> I feel "right" associativity is more natural: (&&)(A, (&&)(B, C)),
>> because the && function is called only once if A is false.
>>
>> I know that redundant && calls are optimized away in most cases.
>> I also know C and C++ standard says: "The && operator groups left-to-right",
>> and most programming languages follow that.
>>
>> But why not "right" associativity?
>> What is the difference between logical operators and ?? operator that has
>> "right" associativity?
>>
>> ___
>> swift-users mailing list
>> swift-users@swift.org
>> https://lists.swift.org/mailman/listinfo/swift-users
>
> ___
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Re: [swift-users] Associativity of && and || operator
Left associativity is most likely just a holdover from the C family–not
conforming with it would break expectations for programmers coming from these
languages. And as you mentioned, the compiler will short-circuit the condition
and stop evaluating as soon as it encounters a false condition, so there’s no
measurable benefit.
Saagar Jha
> On Feb 17, 2017, at 12:54 AM, rintaro ishizaki via swift-users
> wrote:
>
> Hello all,
>
> Why the associativity of Logical{Conjunction,Disjunction}Precedence is "left"?
>
> If you write: A && B && C, it's grouped as (A && B) && C.
> This means that the && function is always called twice: (&&)((&&)(A, B), C).
> I feel "right" associativity is more natural: (&&)(A, (&&)(B, C)),
> because the && function is called only once if A is false.
>
> I know that redundant && calls are optimized away in most cases.
> I also know C and C++ standard says: "The && operator groups left-to-right",
> and most programming languages follow that.
>
> But why not "right" associativity?
> What is the difference between logical operators and ?? operator that has
> "right" associativity?
>
> ___
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> swift-users@swift.org
> https://lists.swift.org/mailman/listinfo/swift-users
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[swift-users] Associativity of && and || operator
Hello all,
Why the associativity of Logical{Conjunction,Disjunction}Precedence is "left
"?
If you write: A && B && C, it's grouped as (A && B) && C.
This means that the && function is *always* called twice: (&&)((&&)(A, B),
C).
I feel "right" associativity is more natural: (&&)(A, (&&)(B, C)),
because the && function is called only once if A is false.
I know that redundant && calls are optimized away in most cases.
I also know C and C++ standard says: "The && operator groups
left-to-right", and most programming languages follow that.
But why not "right" associativity?
What is the difference between logical operators and ?? operator that has "
right" associativity?
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