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 }