• Joel (10/10) Oct 30 2017 The following code assert fails (bar == 1, not -10!). I've wasted
• Jonathan M Davis (15/25) Oct 30 2017 Why would you expect it to be -10? bar is assigned the result of foo() !...
• Joel (1/1) Oct 30 2017 Ok, thanks guys.
• codephantom (16/17) Oct 30 2017 why not throw in some UFCS too...just because you can ;-)
• Adam D. Ruppe (10/11) Oct 30 2017 Not a bug, but I do think it is an iffy design.

Joel <joelcnz gmail.com> writes:

The following code assert fails (bar == 1, not -10!). I've wasted 
a bit of time because of this happening.

void main() {
	if (int bar = foo() != 0) {
		assert(bar == -10);
	}
}

auto foo() {
	return -10;
}

Jonathan M Davis <newsgroup.d jmdavisprog.com> writes:

On Tuesday, October 31, 2017 04:08:12 Joel via Digitalmars-d-learn wrote:
 The following code assert fails (bar == 1, not -10!). I've wasted
 a bit of time because of this happening.

 void main() {
   if (int bar = foo() != 0) {
       assert(bar == -10);
   }
 }

 auto foo() {
   return -10;
 }

Why would you expect it to be -10? bar is assigned the result of foo() != 0,
which is a boolean result and will be either true or false. When that's
assigned to int, a conversion occurs, and that conversion treats true as 1
and false as 0. If you want the result to be -10, then you need to assign
the result of foo() to bar, not the result of foo() != 0. Now, because 0 is
treated as false, you could probably still do

if(int bar = foo())

rather than something like

int bar = foo();
if(bar != 0)

but regardless, the result of foo() != 0 is going to be bool, not int, so
all you'll ever get out of it is true or false, which will then be 1 or 0 if
converted to int.

- Jonathan M Davis

Joel <joelcnz gmail.com> writes:

Ok, thanks guys.

codephantom <me noyb.com> writes:

On Tuesday, 31 October 2017 at 04:27:27 UTC, Joel wrote:
 Ok, thanks guys.

why not throw in some UFCS too...just because you can ;-)

import std.stdio;

void main()
{
     int foo;
     if (foo.bar != 0)  // would be nice if I could do: (int 
foo.bar != 0)
     {
         throw new Exception("foo.bar != 0");
     }
}

auto bar(int x,)
{
     return -10;
}

Adam D. Ruppe <destructionator gmail.com> writes:

On Tuesday, 31 October 2017 at 04:08:12 UTC, Joel wrote:
 	if (int bar = foo() != 0) {

Not a bug, but I do think it is an iffy design.

That is more like:

int bar;
if(bar = (foo() != 0))

so the foo != 0 is evaluated first, which ends up being boolean 
true or false, then THAT true/false value is converted to int and 
assigned to bar, hence it becomes 0 or 1.


You can't really combine declaration and non-trivial comparison 
in a single statement.