Re: __traits(compiles, ...) returns true for syntactic garbage and for semantically incorrect code

[Simen Kjaeraas]

On 2012-42-17 11:12, Pavel <proge...@gmail.com> wrote:

Either I do not understand the work of this feature or it is an obvious bug:

import std.stdio;
import std.conv;

void main()
{

enum string expr = "DMD compiles this garbage ... iiiii - \" #### $$$";

        
    enum bool bTest = __traits(compiles, expr);
    enum bool bTest2 = __traits(compiles, "int i = q{};");
                
    writeln("bTest: " ~ to!string(bTest));
    writeln("bTest2: " ~ to!string(bTest2));
}

Produces (tested with dmd32 2.060 and dmd32 2.059):
   bTest: true
   bTest2: true

(http://dpaste.dzfl.pl/5d338ab3)

Could you please somebody explain this?

Thanks,
Pavel

Let's start off with the obligatory 'You're doing it wrong'.

__traits(compiles, ...) does not check the content of strings.
If you want that, use mixin("somestring").

What your code does is simply check if the string is one that
could be embedded in D code, which both of them can.

If instead of using strings you do this:

   enum bool bTest2 = __traits(compiles, {int i = q{};});

You will see that the result is false.

--
Simen