That's a good point Alan, and I should have mentioned into.
But this came up for me in a situation relevant to Ben's' point.
I was adding or removing a computed sequence of elements of a set based on
some other
input and was using either conj or disj depending on that input, with apply.
It worked on the disj's but failed on the conj's, of course.
I could in this case have made the check at the time of change and used
into or disj
as appropriate, but in general, one might be passed just the functions as
Ben suggests.
Even if there is a better way to handle this problem in this case, I don't
see it as an argument
against the unary conj. The unary conj is conceptually natural, is
consistent with disj, does not
mask bugs, appears to really have no practical downside, and seems to have
at least one useful application.
Why not include it?
On Saturday, November 3, 2012 7:43:22 PM UTC-4, Ben wrote:
>
> There might be a reason to write (apply f coll seqable) in a situation
> in which f might be conj, though.
>
> On Sat, Nov 3, 2012 at 4:25 PM, Alan Malloy <al...@malloys.org<javascript:>>
> wrote:
> > There is never a reason to write (apply conj ...). Instead, use `into`,
> > which does the same thing but faster and with fewer characters.
> >
> >
> > On Saturday, November 3, 2012 3:27:24 PM UTC-7, CGAT wrote:
> >>
> >> It would be nice if clojure.core/conj had a unary implementation
> >>
> >> ([coll] coll)
> >>
> >> The motivating use case is when one is conjoining sequences of
> >> items to a collection all at once:
> >>
> >> (apply conj coll seqable)
> >>
> >> such as (apply conj #{1 2 3} [2 4 6 8 10]).
> >> Currently (1.4.0), this will raise an arity exception
> >> if the seqable object is empty:
> >>
> >> (apply conj #{1 2 3} [])
> >>
> >> necessitating an awkward empty? check when,
> >> for instance, the sequence is computed or passed in.
> >>
> >> It seems to me that making unary conj the identity is both
> >> a natural interpretation and essentially cost free, while
> >> making this use case much more convenient.
> >> Moreover, it is consistent with clojure.core/disj for sets
> >> which does act like this
> >>
> >> (apply disj #{1 2 3} []) -> #{1 2 3}
> >>
> >> and has an identity unary implementation.
> >>
> >> Comments?
> >>
> >>
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>
> --
> Ben Wolfson
> "Human kind has used its intelligence to vary the flavour of drinks,
> which may be sweet, aromatic, fermented or spirit-based. ... Family
> and social life also offer numerous other occasions to consume drinks
> for pleasure." [Larousse, "Drink" entry]
>
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