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
}
