nimforum mirror - What is the meaning of () after an enumeration symbol?

lou15b (orginal) [2023-06-01T18:58:23+02:00] view original

I encountered this while trying to understand the internals of fidgetty. Please note that I'm a newbie when it comes to understanding macros and AST processing.

Apologies for the long post - I am trying to give full context for my question.

First the context.

A couple of types from the cssgrid package are used by fidgetty: GridDir and Constraint.

In gridtypes.nim:

type
  GridDir* = enum
    dcol
    drow

and in constraints.nim (the definition of Constraint is what matters):

ConstraintSizes* = enum
  UiFrac
  UiPerc
  UiFixed

ConstraintSize* = object
  case kind*: ConstraintSizes
  of UiFrac:
    frac*: UiScalar
  of UiPerc:
    perc*: UiScalar
  of UiFixed:
    coord*: UiScalar

Constraints* = enum
  UiNone
  UiValue
  UiAuto
  UiMin
  UiMax
  UiSum
  UiMinMax
  UiEnd

Constraint* = object
  case kind*: Constraints
  of UiNone:
    discard
  of UiValue:
    value*: ConstraintSize
  of UiAuto:
    discard
  of UiMin:
    lmin, rmin*: ConstraintSize
  of UiMax:
    lmax, rmax*: ConstraintSize
  of UiSum:
    lsum, rsum*: ConstraintSize
  of UiMinMax:
    lmm, rmm*: ConstraintSize
  of UiEnd:
    discard

In fidgetty, fidget_dev/common.nim defines a CounterAxisSizingMode enum and a Node class:

CounterAxisSizingMode* = enum
  csAuto
  csFixed
# ...
Node* = ref object
  # ...
  cxSize*: array[GridDir, Constraint]
  # ...

Note the enumeration symbol csAuto above.

Finally, the matter at hand.

In a number of places of fidgetty I see code like the last line in the following excerpt (from fidgetty/fidget_dev.nim). Note that current is a global Node object:

template node(kind: NodeKind, id: static string, inner, setup: untyped): untyped =
  ## Base template for node, frame, rectangle...
  preNode(kind, atom(id))
  setup
  inner
  postNode()
# ...
template frame*(id: static string, inner: untyped): untyped =
  ## Starts a new frame.
  node(nkFrame, id, inner):
    # boxSizeOf parent
    current.cxSize = [csAuto(), csAuto()]

My question is about that last line. In the fidgetty code:

I could not find any definition of csAuto other than in the enum.

I could not find any definition of csAuto() - no proc, template or whatever.

I could not find any definition of a () operator.

In the Nim Manual:

I could not find any mention of the use of () in the section dealing with enumerations.

I could not find any usage of () that was similar to the above in the section dealing with macros - at least, that I could recognize.

So it is a mystery to me what the expression csAuto() means.

Could someone please enlighten me?

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10239 :: What is the meaning of () after an enumeration symbol?