• Jerome BENOIT <g6299304p rezozer.net> Jan 19 2012
• Timon Gehr <timon.gehr gmx.ch> Jan 19 2012
• bearophile <bearophileHUGS lycos.com> Jan 19 2012
• Manfred Nowak <svv1999 hotmail.com> Jan 19 2012

Jerome BENOIT <g6299304p rezozer.net> writes:

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

Timon Gehr <timon.gehr gmx.ch> writes:

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.

bearophile <bearophileHUGS lycos.com> writes:

Timon Gehr:

 I am not very happy about this particular quirk of is expressions:


I'd like to see is expressions a bit re-designed instead of SIMDs added to DMD
:-|

Bye,
bearophile

Manfred Nowak <svv1999 hotmail.com> writes:

bearophile wrote:

 instead of SIMDs added


Most delevopers at the same time like to turf their old errors and are 
keen to do something knew.

-manfred