Concepts: invalid type in this context for var

[mratsim]

The following doesn't compile and gives invalid type in this context for var

Error: invalid type: 'Queue[module_name.FooWrapper]' in this context: 'FooWrapper' for var

type
  Foo = ptr object
    next: Foo

  Enqueueable = concept x, type T
    x is ptr
    x.next is T

  FooWrapper = ptr object
    next: FooWrapper
    foo: Foo
    queue: Queue[FooWrapper]

  Queue[T: Enqueueable] = object
    count: int
    back: T

# Ok so far
var q: Queue[Foo]


# ------------------------------

static: echo FooWrapper is Enqueueable
var fw: FooWrapper

[Araq]

Workaround:Use T instead of Enqueueable and rely on type instantiations to catch mistakes like "foobar has no field named 'next'".

[mratsim]

"All problems in computer science can be solved by another level of indirection" - David Wheeler

The following compiles (declaration order may have a play there, I didn't fully figure out the differences).

type
  Enqueueable* {.explain.} = concept x, type T
    x is ptr
    x.next is T

  Queue*[T: Enqueueable] = object
    count: int
    back: T

  Foo = ptr object
    next: Foo

  FooWrapper = ptr object
    next: FooWrapper
    foo: Foo
    bar: Bar

  Bar = object
    queue: Queue[FooWrapper]

# Ok so far
var q: Queue[Foo]


# ------------------------------

static: echo FooWrapper is Enqueueable
var fw: FooWrapper