[Issue 14771] Hidden @nogc violation around closure creation

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=14771

ag0aep6g at gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ag0aep6g at gmail.com

--- Comment #2 from ag0aep6g at gmail.com ---
A variant is to make makeS a template instead of S.foo:

----
struct S(alias f)
{
    auto foo() { return f(0); }
}

auto makeS()() @nogc
{
    int x = 10;
    S!(a => x) s;
    return s;
}

void main() @nogc
{
    auto s = makeS();
}
----

Compiles, but shouldn't.

Some change in 2.068's Phobos makes it possible to accidentally do this with
std.algorithm.map:

----
import std.algorithm: equal, map;
import std.range: only;

auto foo()(int[] a, immutable int b)
{
    return a.map!(x => x + b);
}

void main() @nogc
{
    int[3] test = [1,2,3];
    assert(test[].foo(3).equal(only(4,5,6)));
}
----

I've seen this twice recently:

http://forum.dlang.org/post/xpdntswucmqboejhxiit@forum.dlang.org
http://forum.dlang.org/post/mrv0td$ci6$1@digitalmars.com

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