I have to say `not_null(v)` reads more like an assertion than a predicate, in
which case `isa<T>(not_null(v))` reads like it has the exact same
semantics that `isa<T>(v)` has currently—asserts that `v` is not null.
I don't dispute that you can *make* it have the desired semantics, it just
won't *look* that way.
maybe `isaT_or_null<Foo>(v)` ? Still looks awkward but maybe less naively
misleading.
From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of Zachary
Turner via llvm-dev
Sent: Saturday, April 06, 2019 10:15 PM
To: Mehdi AMINI
Cc: LLVM Development List; Aaron Ballman
Subject: Re: [llvm-dev] [RFC] Should we add isa_or_null<>?
In that case my original suggestion of isa<T>(not_null(v)) matches the
semantics right?
On Sat, Apr 6, 2019 at 5:03 PM Mehdi AMINI <joker.eph at
gmail.com<mailto:joker.eph at gmail.com>> wrote:
I read `isa<T>(or_null(v))` as "v is a T or nullptr", which
does not match the implementation semantics "v is a T and not null".
On Sat, Apr 6, 2019 at 9:31 PM Zachary Turner <zturner at
google.com<mailto:zturner at google.com>> wrote:
Sorry, brain isn't fully working. I meant to call the function / type
`or_null` instead of `not_null`
On Sat, Apr 6, 2019 at 11:16 AM Zachary Turner <zturner at
google.com<mailto:zturner at google.com>> wrote:
What about a type not_null_impl<T> and we could write:
then you could just write bool x = isa<T>(not_null(val));
We provide a function not_null<T> that returns a not_null_impl<T>:
template<typename T>
not_null_impl<T> not_null(T *t) { return not_null_impl<T>{t}; }
and a specialization of isa that takes a not_null_impl<T>
template<typename T, typename U>
isa<T, not_null_impl<U>>(const not_null_impl<U> &u) {
return u ? isa<T>(*u) : false;
}
On Sat, Apr 6, 2019 at 9:45 AM Mehdi AMINI via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
On Fri, Apr 5, 2019 at 5:15 AM Aaron Ballman via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
On Thu, Apr 4, 2019 at 12:58 PM Chris Lattner <clattner at
nondot.org<mailto:clattner at nondot.org>>
wrote:>
>
>
> > On Apr 4, 2019, at 5:37 AM, Don Hinton via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
> >
> > I'd like to propose adding `isa_or_null<>` to replace the
following usage pattern that's relatively common in conditionals:
> >
> > var && isa<T>(var) =>>
isa_or_null<T>(var)
> >
> > And in particular when `var` is a method call which might be
expensive, e.g.:
> >
> > X->foo() && isa<T>(X->foo()) =>>
isa_or_null<T>(X->foo())
> >
> > The implementation could be a simple wrapper around isa<>, and
while the IR produced is only slightly more efficient, the elimination of an
extra call could be worthwhile.
>
> I’d love to see this, I agree with downstream comments though that this
name will be confusing. isa_and_nonnull<>. ?
tbh, I don't think the proposed name will be all that confusing --
I am with David on this, this sounds like misleading naming to me, I would
expect true on null value when reading : if (isa_or_null<T>(var))
we're used to _or_null() returning "the right thing" when given
null.
I think we're used to have "the right thing" because the name
matches the semantic: the "_or_null()" suffix matches the semantics a
conversion operator that returns nullptr on failure.
It does not translate with isa<> IMO.
isa_and_nonnull<> is a bit of a weird name for me, but I could
probably live with it. We could spell it nonnull_and_isa<> to reflect
the order of the operations, but that sort of hides the important part
of the API (the "isa" bit).
isa_nonnulll works fine for me, isa_and_nonnull is a bit verbose but seems OK as
well.
For nonnull_and_isa<T>(val) ; it starts to look strangely close to the
pattern !val && isa<T>(val) ; and I'm not sure it is really
such a readability improvement anymore?
--
Mehdi
~Aaron
>
> -Chris
>
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Bruno Ricci via llvm-dev
2019-Apr-07 14:40 UTC
[llvm-dev] [RFC] Should we add isa_or_null<>?
On 07/04/2019 14:13, via llvm-dev wrote:> I have to say `not_null(v)` reads more like an assertion than a predicate, in which case `isa<T>(not_null(v))` reads like it has the exact same semantics that `isa<T>(v)` has currently—asserts that `v` is not null. > > I don't dispute that you can *make* it have the desired semantics, it just won't *look* that way. > > > > maybe `isaT_or_null<Foo>(v)` ? Still looks awkward but maybe less naively misleading. >... or we keep using "v && isa<T>(v)" (which is not even longer!), which is unambiguous for everyone. In the rare special case where the pattern "someExpensiveCall() && isa<T>(someExpensiveCall())" is used, just assign the result of "someExpensiveCall()" to a variable. Bruno> > > > > *From:*llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of *Zachary Turner via llvm-dev > *Sent:* Saturday, April 06, 2019 10:15 PM > *To:* Mehdi AMINI > *Cc:* LLVM Development List; Aaron Ballman > *Subject:* Re: [llvm-dev] [RFC] Should we add isa_or_null<>? > > > > In that case my original suggestion of isa<T>(not_null(v)) matches the semantics right? > > > > On Sat, Apr 6, 2019 at 5:03 PM Mehdi AMINI <joker.eph at gmail.com <mailto:joker.eph at gmail.com>> wrote: > > I read `isa<T>(or_null(v))` as "v is a T or nullptr", which does not match the implementation semantics "v is a T and not null". > > > > On Sat, Apr 6, 2019 at 9:31 PM Zachary Turner <zturner at google.com <mailto:zturner at google.com>> wrote: > > Sorry, brain isn't fully working. I meant to call the function / type `or_null` instead of `not_null` > > > > On Sat, Apr 6, 2019 at 11:16 AM Zachary Turner <zturner at google.com <mailto:zturner at google.com>> wrote: > > What about a type not_null_impl<T> and we could write: > > > > then you could just write bool x = isa<T>(not_null(val)); > > > > We provide a function not_null<T> that returns a not_null_impl<T>: > > > > template<typename T> > > not_null_impl<T> not_null(T *t) { return not_null_impl<T>{t}; } > > > > and a specialization of isa that takes a not_null_impl<T> > > > > template<typename T, typename U> > > isa<T, not_null_impl<U>>(const not_null_impl<U> &u) { > > return u ? isa<T>(*u) : false; > > } > > > > On Sat, Apr 6, 2019 at 9:45 AM Mehdi AMINI via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote: > > > > > > On Fri, Apr 5, 2019 at 5:15 AM Aaron Ballman via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote: > > On Thu, Apr 4, 2019 at 12:58 PM Chris Lattner <clattner at nondot.org <mailto:clattner at nondot.org>> wrote: > > > > > > > > > On Apr 4, 2019, at 5:37 AM, Don Hinton via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote: > > > > > > I'd like to propose adding `isa_or_null<>` to replace the following usage pattern that's relatively common in conditionals: > > > > > > var && isa<T>(var) =>> isa_or_null<T>(var) > > > > > > And in particular when `var` is a method call which might be expensive, e.g.: > > > > > > X->foo() && isa<T>(X->foo()) =>> isa_or_null<T>(X->foo()) > > > > > > The implementation could be a simple wrapper around isa<>, and while the IR produced is only slightly more efficient, the elimination of an extra call could be worthwhile. > > > > I’d love to see this, I agree with downstream comments though that this name will be confusing. isa_and_nonnull<>. ? > > tbh, I don't think the proposed name will be all that confusing -- > > > > I am with David on this, this sounds like misleading naming to me, I would expect true on null value when reading : if (isa_or_null<T>(var)) > > > > we're used to _or_null() returning "the right thing" when given null. > > > > I think we're used to have "the right thing" because the name matches the semantic: the "_or_null()" suffix matches the semantics a conversion operator that returns nullptr on failure. > > It does not translate with isa<> IMO. > > > > > > isa_and_nonnull<> is a bit of a weird name for me, but I could > probably live with it. We could spell it nonnull_and_isa<> to reflect > the order of the operations, but that sort of hides the important part > of the API (the "isa" bit). > > > > isa_nonnulll works fine for me, isa_and_nonnull is a bit verbose but seems OK as well. > > > > For nonnull_and_isa<T>(val) ; it starts to look strangely close to the pattern !val && isa<T>(val) ; and I'm not sure it is really such a readability improvement anymore? > > > > -- > > Mehdi > > > > > > > ~Aaron > > > > > -Chris > > > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev > > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev > > > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev >
David Greene via llvm-dev
2019-Apr-08 18:33 UTC
[llvm-dev] [RFC] Should we add isa_or_null<>?
Bruno Ricci via llvm-dev <llvm-dev at lists.llvm.org> writes:> On 07/04/2019 14:13, via llvm-dev wrote: >> I have to say `not_null(v)` reads more like an assertion than a >> predicate, in which case `isa<T>(not_null(v))` reads like it has the >> exact same semantics that `isa<T>(v)` has currently—asserts that `v` >> is not null. >> >> I don't dispute that you can *make* it have the desired semantics, it just won't *look* that way. >> >> >> >> maybe `isaT_or_null<Foo>(v)` ? Still looks awkward but maybe less naively misleading. >> > > ... or we keep using "v && isa<T>(v)" (which is not even longer!), which is unambiguous for everyone. > In the rare special case where the pattern "someExpensiveCall() && isa<T>(someExpensiveCall())" is used, > just assign the result of "someExpensiveCall()" to a variable.+1. -David