Can someone help me understand the details around why this fails?

import std;

struct W(T) {
    T value;
    auto hook(handlers...)() {
        return handlers[0](value);
    }
}

template f(handlers...) {
    auto ref f(T)(auto ref T value) {
        return value.hook!handlers;
    }
}

@nogc void main() {
    auto a = W!int(3);
    auto b = a.f!((_) => "yes");
}

If I specifically type the lambda I pass in to f (i.e. (int _) => "yes") then it works. Or if I make hook a global template that takes a W!T as the first parameter it also works. Is there a work around for this?

On Friday, 26 July 2019 at 16:20:10 UTC, aliak wrote:
> Can someone help me understand the details around why this fails?
>
> import std;
>
> struct W(T) {
>     T value;
>     auto hook(handlers...)() {
>         return handlers[0](value);
>     }
> }
>
> template f(handlers...) {
>     auto ref f(T)(auto ref T value) {
>         return value.hook!handlers;
>     }
> }
>
> @nogc void main() {
>     auto a = W!int(3);
>     auto b = a.f!((_) => "yes");
> }
>
> If I specifically type the lambda I pass in to f (i.e. (int _) => "yes") then it works. Or if I make hook a global template that takes a W!T as the first parameter it also works. Is there a work around for this?

Err sorry, that was ldc pre the 5710 bug fix. In DMD I get this:

Error: @nogc function D main cannot call non-@nogc function onlineapp.main.f!(W!int).f

I guess it's allocating a delegate somewhere. Can I fix that?

On Friday, 26 July 2019 at 16:21:52 UTC, aliak wrote:
> On Friday, 26 July 2019 at 16:20:10 UTC, aliak wrote:
>> Can someone help me understand the details around why this fails?
>>
>> import std;
>>
>> struct W(T) {
>>     T value;
>>     auto hook(handlers...)() {
>>         return handlers[0](value);
>>     }
>> }
>>
>> template f(handlers...) {
>>     auto ref f(T)(auto ref T value) {
>>         return value.hook!handlers;
>>     }
>> }
>>
>> @nogc void main() {
>>     auto a = W!int(3);
>>     auto b = a.f!((_) => "yes");
>> }
>>
>> If I specifically type the lambda I pass in to f (i.e. (int _) => "yes") then it works. Or if I make hook a global template that takes a W!T as the first parameter it also works. Is there a work around for this?
>
> Err sorry, that was ldc pre the 5710 bug fix. In DMD I get this:
>
> Error: @nogc function D main cannot call non-@nogc function onlineapp.main.f!(W!int).f
>
> I guess it's allocating a delegate somewhere. Can I fix that?

I can do this but ugh:

import std;

struct W(T) {
    T value;
    static auto hook(handlers...)(auto ref typeof(this) self) {
        return handlers[0](self.value);
    }
}

template f(handlers...) {
    auto ref f(T)(auto ref T value) {
        return value.hook!handlers(value);
    }
}

@nogc void main() {
    auto a = W!int(3);
    auto b = a.f!((_) => "yes");
}