Re: =?windows-1252?Q?Java's_Broken_Booleans?=

From:

Joshua Cranmer <Pidgeot18@verizon.invalid>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 15 Feb 2011 11:21:17 -0500

Message-ID:

<ije95t$sbo$1@news.eternal-september.org>

On 02/15/2011 10:44 AM, Andreas Leitgeb wrote:

Joshua Cranmer<Pidgeot18@verizon.invalid> wrote:

I'm quite comfortable with Java's restrictive way for conversion
towards boolean, but a bit unhappy about the other direction -
maybe this feeling was triggered by the truely moronic looking
byte code generated for the "bool?1:0" idiom.

Btw., [...]
    11: iload_1
    12: ifeq 19
    15: iconst_1
    16: goto 20
    19: iconst_0
    20: istore_2

Well, to be fair, there is nothing in the JVM that actually guarantees
that true == 1; the typical connotation is that nonzero is true [...]
In any case, I suspect the JIT would rip all those checks out,

How could it, when it doesn't even know the concept of "boolean"?

Assuming that the JIT does tracing, it can observe that the result of
var1 is always 0 or 1, which would cause the statement to become
equivalent to var2 = var1. From there, it can further do elimination to
remove var2. It's possible, but I do not know if the JVM does it.

--
Beware of bugs in the above code; I have only proved it correct, not
tried it. -- Donald E. Knuth