user=> (binding [*unchecked-math* true] (map int [33 77 0xffffffff]))
#<IllegalArgumentException java.lang.IllegalArgumentException: Value out of
range for int: 4294967295>
The cause of this:
(defn int
"Coerce to int"
{
:inline (fn [x] `(. clojure.lang.RT (~(if *unchecked-math*
'uncheckedIntCast 'intCast) ~x)))
:added "1.0"}
[x] (. clojure.lang.RT (intCast x)))
The inline and non-inline version don't coincide -- the non-inline version
lacks the check for *unchecked-math*.
On top of that, the inline version sort-of doesn't work anyway --
specifically, it doesn't work if you do "the obvious":
user=> (binding [*unchecked-math* true] (int 0xffffffff))
#<IllegalArgumentException java.lang.IllegalArgumentException: Value out of
range for int: 4294967295>
user=> (defn foo [] (binding [*unchecked-math* true] (int 0xffffffff)))
#'user/foo
user=> (foo)
#<IllegalArgumentException java.lang.IllegalArgumentException: Value out of
range for int: 4294967295>
The problem there is apparently that it checks *unchecked-math* at
macroexpansion time, and of course binding it at runtime to do some
unchecked math therefore binds it too late to influence the int function.
If this is intentional, to avoid expensive runtime checks of dynamic Vars,
then there are two additional problems.
First, there's the apparent lack of an unchecked-int function, or similar,
that either is unchecked or checks *unchecked-math* at runtime, for those
who want dynamic behavior even if there's a cost.
Without this, there's no way to get unchecked int casts in map and other
HOFs short of ugly hacks like #(int %) or
#(clojure.lang.RT/uncheckedIntCast %).
Another use case would be when using ints not for speed but because you
want a 32-bit wraparound integer for some other purpose, such as talking to
I/O devices or legacy file formats that want such things, or to implement
certain algorithms that rely heavily on wraparound and bit arithmetic in a
relatively speed-insensitive context, likely where I/O is the bottleneck.
Furthermore, though (do (set! *unchecked-math* true) (println (int
0xffffffff)) (set! *unchecked-math* false)) works, it is ugly as sin and
set! is (usually) evil.
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