is there any way to get error from speculative execution (`__traits(
compiles, ...)`)? would be useful in tests; If not currently how hard
would that be to implement? eg:

```

struct Status{bool ok; string msg;}

Status status = __traits(compilesReportError, {string b=10;})
assert(!status.ok);
assert(status.msg==`main.d(15) Error: cannot implicitly convert
expression 10 of type int to string`);
```

On Wednesday, 7 February 2018 at 20:29:44 UTC, Timothee Cour wrote:
> is there any way to get error from speculative execution (`__traits(
> compiles, ...)`)? would be useful in tests; If not currently how hard
> would that be to implement? eg:
>
> ```
>
> struct Status{bool ok; string msg;}
>
> Status status = __traits(compilesReportError, {string b=10;})
> assert(!status.ok);
> assert(status.msg==`main.d(15) Error: cannot implicitly convert
> expression 10 of type int to string`);
> ```

Probably not very hard. Would make for some nice diagnostics,but very flakey tests. Compiler errors are frequently changed.

understood, but that's responsibility of tester to make sure they're
not too flaky (eg using msg.canFind("FOO") (or, if regex weren't slow,
regex)



On Wed, Feb 7, 2018 at 1:13 PM, Nicholas Wilson via Digitalmars-d <digitalmars-d@puremagic.com> wrote:
> On Wednesday, 7 February 2018 at 20:29:44 UTC, Timothee Cour wrote:
>>
>> is there any way to get error from speculative execution (`__traits(
>> compiles, ...)`)? would be useful in tests; If not currently how hard
>> would that be to implement? eg:
>>
>> ```
>>
>> struct Status{bool ok; string msg;}
>>
>> Status status = __traits(compilesReportError, {string b=10;})
>> assert(!status.ok);
>> assert(status.msg==`main.d(15) Error: cannot implicitly convert
>> expression 10 of type int to string`);
>> ```
>
>
> Probably not very hard. Would make for some nice diagnostics,but very flakey tests. Compiler errors are frequently changed.

On Wednesday, 7 February 2018 at 20:29:44 UTC, Timothee Cour wrote:
> is there any way to get error from speculative execution (`__traits(
> compiles, ...)`)? would be useful in tests; If not currently how hard
> would that be to implement? eg:
>
> ```
>
> struct Status{bool ok; string msg;}
>
> Status status = __traits(compilesReportError, {string b=10;})
> assert(!status.ok);
> assert(status.msg==`main.d(15) Error: cannot implicitly convert
> expression 10 of type int to string`);
> ```

static if(!__traits(compiles, $CODE)) {
    $CODE
}

It's the same technique I use in concepts to produce an error message if a struct you wanted to be, say isInputRange, isn't:

https://github.com/atilaneves/concepts

Atila