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clarify docs for wrapnils (#16929)

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Co-authored-by: Dominik Picheta <dominikpicheta@googlemail.com>
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Timothee Cour 2021-02-04 15:39:19 -08:00 • committed by GitHub
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9
lib/std/wrapnils.nim
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@ -19,8 +19,13 @@ runnableExamples:
assert ?.f2.x1 == "a" # same as f2.x1 (no nil LHS in this chain)
assert ?.Foo(x1: "a").x1 == "a" # can use constructor inside
# when you know a sub-expression is not nil, you can scope it as follows:
assert ?.(f2.x2.x2).x3[] == 0 # because `f` is nil
# when you know a sub-expression doesn't involve a `nil` (e.g. `f2.x2.x2`),
# you can scope it as follows:
assert ?.(f2.x2.x2).x3[] == 0
assert (?.f2.x2.x2).x3 == nil # this terminates ?. early
import segfaults # enable `NilAccessDefect` exceptions
doAssertRaises(NilAccessDefect): echo (?.f2.x2.x2).x3[]
type Wrapnil[T] = object
valueImpl: T