On 01/19/2012 05:41 PM, Jerome BENOIT wrote:
Hello List:
On my box, the following D source, inspired by the subsection 5.6.1 of
tDpl,
does not work as expected:
-
// adhoc_06.d
import std.stdio;
unittest {
// Tersest, most convenient code
auto f = (int i) {};
writeln(typeid(f));
assert(is(f == function));
}
void main() {}
-
I get:
void delegate()
core.exception.AssertError@adhoc_06.d(7): unittest failure
According to the book, the assertion is true and f is a function
but not a literal.
What is going wrong ?
Thanks in advance,
Jerome
Many things, actually. You are looking at both an error in TDPL and a
compiler bug. The compiler bug is already fixed in git head and will not
exist in the next release. See
http://d.puremagic.com/issues/show_bug.cgi?id=3235
In the line:
auto f = (int i) {};
f is deduced as void delegate(int) pure nothrow @safe instead of as void
function(int) pure nothrow @safe. This is the compiler bug that has been
fixed.
In the line:
assert(is(f == function));
TDPL contains an error. Is expressions can be used to query some
properties of types. If an involved type is not a well-formed type the
result is false. Since f is a variable and not a type, the is expression
yields false. is(T == function) tests whether or not T is a function
type. Therefore, the line should actually read is(typeof(*f)==function),
as f is a function pointer.
I am not very happy about this particular quirk of is expressions:
void delegate() dg; // declares a delegate
void function() fp; // declares a function _pointer_
assert( is(typeof(dg) == delegate));
assert(!is(typeof(fp) == function)); // the is expression tests whether
it is a function, not whether it is a function pointer
assert(is(typeof(*fp) == function));
You may want to use std.traits.IsFunctionPointer and
std.traits.IsDelegate instead.
