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123 lines
4.3 KiB
Nim
123 lines
4.3 KiB
Nim
template accept(x) =
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static: assert compiles(x)
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template reject(x) =
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static: assert(not compiles(x))
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{.experimental: "notnil".}
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type
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TRefObj = ref object
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x: int
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THasNotNils = object of RootObj
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a: TRefObj not nil
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b: TRefObj not nil
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c: TRefObj
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THasNotNilsRef = ref THasNotNils
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TChoice = enum A, B, C, D, E, F
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TBaseHasNotNils = object of THasNotNils
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case choice: TChoice
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of A:
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moreNotNils: THasNotNils
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of B:
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indirectNotNils: ref THasNotNils
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else:
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discard
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TObj = object
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case choice: TChoice
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of A:
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a: int
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of B, C:
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bc: int
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of D:
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d: TRefObj
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of E:
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e1: TRefObj
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e2: int
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else:
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f: string
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TNestedChoices = object
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case outerChoice: bool
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of true:
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truthy: int
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else:
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case innerChoice: TChoice
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of A:
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a: int
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of B:
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b: int
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else:
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notnil: TRefObj not nil
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var x = D
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var nilRef: TRefObj
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var notNilRef = TRefObj(x: 20)
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proc makeHasNotNils: ref THasNotNils =
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result.a = TRefObj(x: 10)
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result.b = TRefObj(x: 20)
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accept TObj()
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accept TObj(choice: A)
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reject TObj(choice: A, bc: 10) # bc is in the wrong branch
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accept TObj(choice: B, bc: 20)
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reject TObj(a: 10) # branch selected without providing discriminator
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reject TObj(choice: x, a: 10) # the discrimantor must be a compile-time value when a branch is selected
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accept TObj(choice: x) # it's OK to use run-time value when a branch is not selected
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accept TObj(choice: F, f: "") # match an else clause
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reject TObj(f: "") # the discriminator must still be provided for an else clause
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reject TObj(a: 10, f: "") # conflicting fields
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accept TObj(choice: E, e1: TRefObj(x: 10), e2: 10)
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accept THasNotNils(a: notNilRef, b: notNilRef, c: nilRef)
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# XXX: the "not nil" logic in the compiler is not strong enough to catch this one yet:
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# reject THasNotNils(a: notNilRef, b: nilRef, c: nilRef)
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reject THasNotNils(b: notNilRef, c: notNilRef) # there is a missing not nil field
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reject THasNotNils() # again, missing fields
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accept THasNotNils(a: notNilRef, b: notNilRef) # it's OK to omit a non-mandatory field
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# missing not nils in base
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reject TBaseHasNotNils()
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# once you take care of them, it's ok
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accept TBaseHasNotNils(a: notNilRef, b: notNilRef, choice: D)
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# this one is tricky!
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# it has to be rejected, because choice gets value A by default (0) and this means
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# that the THasNotNils field will be active (and it will demand more initialized fields).
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reject TBaseHasNotNils(a: notNilRef, b: notNilRef)
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# you can select a branch without mandatory fields
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accept TBaseHasNotNils(a: notNilRef, b: notNilRef, choice: B)
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accept TBaseHasNotNils(a: notNilRef, b: notNilRef, choice: B, indirectNotNils: nil)
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# but once you select a branch with mandatory fields, you must specify them
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reject TBaseHasNotNils(a: notNilRef, b: notNilRef, choice: A)
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reject TBaseHasNotNils(a: notNilRef, b: notNilRef, choice: A, indirectNotNils: nil)
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reject TBaseHasNotNils(a: notNilRef, b: notNilRef, choice: A, moreNotNils: THasNotNils())
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accept TBaseHasNotNils(a: notNilRef, b: notNilRef, choice: A, moreNotNils: THasNotNils(a: notNilRef, b: notNilRef))
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# all rules apply to sub-objects as well
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accept TBaseHasNotNils(a: notNilRef, b: notNilRef, choice: B, indirectNotNils: makeHasNotNils())
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reject TBaseHasNotNils(a: notNilRef, b: notNilRef, choice: B, indirectNotNils: THasNotNilsRef())
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accept TBaseHasNotNils(a: notNilRef, b: notNilRef, choice: B, indirectNotNils: THasNotNilsRef(a: notNilRef, b: notNilRef))
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# this will be accepted, because the false outer branch will be taken and the inner A branch
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accept TNestedChoices()
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# but if we supply a run-time value for the inner branch, the compiler won't be able to prove
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# that the notnil field was initialized
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reject TNestedChoices(outerChoice: false, innerChoice: x) # XXX: The error message is not very good here
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reject TNestedChoices(outerChoice: true, innerChoice: A) # XXX: The error message is not very good here
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accept TNestedChoices(outerChoice: false, innerChoice: B)
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reject TNestedChoices(outerChoice: false, innerChoice: C)
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accept TNestedChoices(outerChoice: false, innerChoice: C, notnil: notNilRef)
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reject TNestedChoices(outerChoice: false, innerChoice: C, notnil: nil)
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