Here's a sneaky little bug

[KennyTM~]

On Jun 25, 11 02:44, Jimmy Cao wrote:
>
>
> On Fri, Jun 24, 2011 at 1:28 PM, Andrej Mitrovic
> <andrej.mitrovich at gmail.com <mailto:andrej.mitrovich at gmail.com>> wrote:
>
>     import std.stdio;
>
>     void main()
>     {
>         bool state = false;
>         writeln("state is: " ~ state ? "true" : "false");
>     }
>
>     writes:
>     true
>
>     Whoa, what happened? Well, this should explain things:
>
>         bool state = false;
>         auto str = "bla" ~ state;
>
>     What (I assume) happens is the state boolean is converted to an int,
>     and since chars are ints in disguise and interchangeable you can
>     concatenate them with strings.
>
>     So the original code acted like it was written like this:
>         bool state = false;
>         writeln(("state is: " ~ state) ? "true" : "false");
>
>     And what we wanted was this:
>         bool state = false;
>         writeln("state is: " ~ (state ? "true" : "false"));
>
>     Anyway I just wanted to share how forgetting parens can introduce
>     bugs in code.
>
>
> Why can ints be so easily concatenated with strings in the first place?

Because 'int' is convertible to a 'dchar'. (I have a patch based on 
Value Range Propagation against this, but it breaks a lot of druntime 
and Phobos code.)