template isCallableCTFE(alias fun){
template isCallableCTFE_aux(alias T){
enum isCallableCTFE_aux=T;
}
enum isCallableCTFE=__traits(compiles,isCallableCTFE_aux!(fun()));
}

template isCallableCTFE2(fun...){
enum isCallableCTFE2=true;
}


unittest{
int fun1(){
return 1;
}
auto fun1_N(){
import std.array;
//would return Error: gc_malloc cannot be interpreted at compile time,
because it has no available source code due to a bug
return [1].array;
}
int fun2(int x){
return 1;
}
auto fun2_N(int x){
import std.array;
//same as fun1_N
return [1].array;
}

int a1;
enum a2=0;

static assert(!isCallableCTFE!(()=>a1));
static assert(isCallableCTFE!(()=>a2));

static assert(isCallableCTFE!fun1);
static assert(!isCallableCTFE!fun1_N);

static assert(isCallableCTFE!(()=>fun2(0)));
static assert(!isCallableCTFE!(()=>fun2_N(0)));
//NOTE:an alternate syntax which could be implemented would be: static
assert(!isCallableCTFE!(fun2_N,0)));
}

On Thursday, 11 July 2013 at 02:17:13 UTC, Timothee Cour wrote:
> template isCallableCTFE(alias fun){
> template isCallableCTFE_aux(alias T){
> enum isCallableCTFE_aux=T;
> }
> enum isCallableCTFE=__traits(compiles,isCallableCTFE_aux!(fun()));
> }
>
> template isCallableCTFE2(fun...){
> enum isCallableCTFE2=true;
> }
>
>
> unittest{
> int fun1(){
> return 1;
> }
> auto fun1_N(){
> import std.array;
> //would return Error: gc_malloc cannot be interpreted at compile time,
> because it has no available source code due to a bug
> return [1].array;
> }
> int fun2(int x){
> return 1;
> }
> auto fun2_N(int x){
> import std.array;
> //same as fun1_N
> return [1].array;
> }
>
> int a1;
> enum a2=0;
>
> static assert(!isCallableCTFE!(()=>a1));
> static assert(isCallableCTFE!(()=>a2));
>
> static assert(isCallableCTFE!fun1);
> static assert(!isCallableCTFE!fun1_N);
>
> static assert(isCallableCTFE!(()=>fun2(0)));
> static assert(!isCallableCTFE!(()=>fun2_N(0)));
> //NOTE:an alternate syntax which could be implemented would be: static
> assert(!isCallableCTFE!(fun2_N,0)));
> }


can we add this to std.traits?
it allows (among other things) to write unittests for CTFE, etc.

On Thursday, 11 July 2013 at 03:10:38 UTC, timotheecour wrote:
> On Thursday, 11 July 2013 at 02:17:13 UTC, Timothee Cour wrote:
[snip]
>
> can we add this to std.traits?
> it allows (among other things) to write unittests for CTFE, etc.

Phobos has an internal helper function for testing CTFEable.
https://github.com/D-Programming-Language/phobos/blob/master/std/exception.d#L1322

Kenji Hara

On Thursday, 11 July 2013 at 03:29:13 UTC, Kenji Hara wrote:
> On Thursday, 11 July 2013 at 03:10:38 UTC, timotheecour wrote:
>> On Thursday, 11 July 2013 at 02:17:13 UTC, Timothee Cour wrote:
> [snip]
>>
>> can we add this to std.traits?
>> it allows (among other things) to write unittests for CTFE, etc.
>
> Phobos has an internal helper function for testing CTFEable.
> https://github.com/D-Programming-Language/phobos/blob/master/std/exception.d#L1322
>
> Kenji Hara


Mine is more flexible. The one you mention can only work in a static assert statement.
We could replace it in terms of static assert(isCallableCTFE!dg) but not vice versa.