I ran into a strange and hard-to-describe problem with nested functions closing over the argument to their enclosing function.

When a nested function (A) returns the value of another nested function (B) that returns a parameter of the enclosing function (C), and when (A) is returned from (C), then calling (A) returns an incorrect value if (A) has a parameter of class type (it works when (A) has no class parameters).

The code below demonstrates this (using DMD 2.058, no optimizations). Is this a bug?


auto foo(T)(int val)
{
    int nested()
    {
        return val;
    }

    int escaping(T ignored)
    {
        return nested();
    }

    return &escaping;

//    return &nested; // this works
}

struct Bar {}

class Baz {}

void main()
{
    auto func1 = foo!int(55);
    auto val1 = func1(12);
    assert(val1 == 55); // works fine with integral type

    auto func2 = foo!Bar(55);
    Bar bar;
    auto val2 = func2(bar);
    assert(val2 == 55); // works fine with struct

    auto func3 = foo!Baz(55);
    auto baz = new Baz();
    auto val3 = func3(baz);
    assert(val3 == 55); // fails; val3 is different value on each run
}

On 3/30/2012 1:13 PM, Ed McCardell wrote:
>
> I ran into a strange and hard-to-describe problem with nested functions closing
> over the argument to their enclosing function.
>
> When a nested function (A) returns the value of another nested function (B) that
> returns a parameter of the enclosing function (C), and when (A) is returned from
> (C), then calling (A) returns an incorrect value if (A) has a parameter of class
> type (it works when (A) has no class parameters).
>
> The code below demonstrates this (using DMD 2.058, no optimizations). Is this a
> bug?

Looks like one. Please report this to

http://d.puremagic.com/issues/enter_bug.cgi?product=D

On 3/30/12, Ed McCardell <edmccard@hotmail.com> wrote:
> The code below demonstrates this (using DMD 2.058, no optimizations). Is
> this a bug?

You mean the result is 55 when you uncomment "return &nested;"? All asserts pass for me when I use that return. Otherwise when using "return &escaping;" I get:

1244764
1244764
4202631

2.058 win32.

On 03/30/2012 04:51 PM, Andrej Mitrovic wrote:
> You mean the result is 55 when you uncomment "return&nested;"? All
> asserts pass for me when I use that return. Otherwise when using
> "return&escaping;" I get:
>
> 1244764
> 1244764
> 4202631
>
> 2.058 win32.

On 64-bit linux, the first two asserts always pass using either "return &nested" or "return &escaping". Just checked on 32-bit linux and I see the same behavior you are, with all three asserts failing using "return &escaping".

--Ed

On 03/30/2012 04:45 PM, Walter Bright wrote:
> On 3/30/2012 1:13 PM, Ed McCardell wrote:
>> The code below demonstrates this (using DMD 2.058, no optimizations).
>> Is this a
>> bug?
>
> Looks like one. Please report this to
>
> http://d.puremagic.com/issues/enter_bug.cgi?product=D

Done:

http://d.puremagic.com/issues/show_bug.cgi?id=7801