[PATCH] D42027: [Support][NFC] Improve isa implementation

[David Blaikie via llvm-commits]

In retrospect is it useful for Optional to be supported in isa? Since its
dynamic type is the same as its static type?

On Tue, Jan 23, 2018 at 10:50 PM Dmitry Borisenkov via Phabricator <
reviews at reviews.llvm.org> wrote:

> dmitry added inline comments.
>
>
> ================
> Comment at: unittests/Support/Casting.cpp:288-289
> +  EXPECT_TRUE(isa<Base>(DShared));
> +  llvm::Optional<Derived> DOpt;
> +  EXPECT_TRUE(isa<Base>(DOpt));
> +}
> ----------------
> dblaikie wrote:
> > Does this change then mean that one could cast<T> from Optional<Derived>
> to Optional<Base>? Because that'd be problematic, owing to Optional being a
> value-type. (it'd slice the object)
> This change doesn't modify casts behavior - just isa.
> As for the plan, cast should return T*, so
> ```
> Optional<Derived> DOpt;
> Base *b = cast<Base>(DOpt); //Just cast pointer to underlying data to
> Base*, does not handle potential ownership issues.
> ```
> should work, but it's ok.
> Move cast would be indeed problematic for value-types. So I would probably
> restrict it.
>
>
> https://reviews.llvm.org/D42027
>
>
>
>
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