nogc callback inferred as non-nogc

[dlangBugzillaToGithub]

Ali Ak reported this on 2019-07-29T22:32:23Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=20091

CC List

• Steven Schveighoffer (@schveiguy)

Description

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");
}

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

Adding @nogc on function f says hook!((_) => "yes").hook closes over variable __this310

If you explicitly specify a type on the lambda that you pass to f then it compiles:

auto b = a.f!((int) => "yes");

[dlangBugzillaToGithub]

ali.akhtarzada commented on 2019-07-29T23:21:16Z

f's instantiation with untyped lambda:

f!(W!int)
{
	auto pure nothrow @safe string f(ref W!int value)
	{
		return (void*[2] __this3 = null;) , value.hook();
	}

}

With typed lambda:

f!(W!int)
{
	auto pure nothrow @nogc @safe string f(ref W!int value)
	{
		return value.hook();
	}

}