On 5/15/14, 1:31 AM, Jonathan M Davis via Digitalmars-d-learn wrote:
On Thu, 15 May 2014 01:29:23 +0000
Kapps via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com> wrote:
On Wednesday, 14 May 2014 at 23:50:34 UTC, Meta wrote:
On the topic of lazy, why *is* it so slow, exactly? I thought
it was just shorthand for taking a function that evaluates the
expression, and wrapping said expression in that function at
the call site. That is, I thought that:
int doSomething(lazy int n)
{
return n();
}
Was more or less equivalent to:
int doSomething(int function(int) n)
{
return n();
}
It's more equivalent to:
int doSomething(int delegate(int) n)
{
return n();
}
And (I could be very likely wrong here), I believe that it's
expensive because it's not scope and possibly requires a closure.
Again, very likely may be wrong.
Yeah. It generates a delegate. You even use the value internally as a
delegate. So, that's definitely part of the problem, though IIRC, there were
other issues with it. However, I don't remember at the moment. The big one
IIRC (which may be due to its nature as a delegate) is simply that it can't be
inlined, and in many cases, you very much what the code to be inlined (enforce
would be a prime example of that).
enforce(cond, "failure");
really should just translate to something close to
if(!cond) throw new Exception("failure");
but it doesn't do anything close to that.
Isn't there a way in D to just expand:
enforce(cond, "failure");
(or something with a similar syntax) to this, at compile-time:
if(!cond) throw new Exception("failure");
I thought D could do this, so enforce should do this instead of using
lazy arguments.
