From: Rusty Russell <rusty@rustcorp.com.au>
To: Yubin Ruan <ablacktshirt@gmail.com>, ccan@lists.ozlabs.org
Subject: Re: useless expression in typesaft_cb_cast
Date: Tue, 13 Mar 2018 20:19:45 +1030 [thread overview]
Message-ID: <874llkl2yu.fsf@rustcorp.com.au> (raw)
In-Reply-To: <20180311200527.GF6146@HP>
Yubin Ruan <ablacktshirt@gmail.com> writes:
> Hi,
>
> typesaft_cb_cast() is defined in typesaft_cb.h as:
>
> #define typesafe_cb_cast(desttype, oktype, expr) \
> __builtin_choose_expr( \
> __builtin_types_compatible_p(__typeof__(0?(expr):(expr)), \
> oktype), \
> (desttype)(expr), (expr))
>
> what is the point of that "0?(expr):(expr)" ?
Hi Yubin!
I had to search through git history to find it! It serves to
decay a function type to a function pointer, otherwise
__builtin_types_compatible_p(func, functype) returns false because
func isn't a pointer to a function, it's a function.
Cheers,
Rusty.
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prev parent reply other threads:[~2018-03-13 9:56 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-11 20:05 useless expression in typesaft_cb_cast Yubin Ruan
2018-03-13 9:49 ` Rusty Russell [this message]
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