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refactor: Replace ref-cell late-binding with let mutable in PreCompute #294

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refactor: Replace ref-cell late-binding with let mutable in PreCompute #294

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22 changes: 14 additions & 8 deletions src/Argu/PreCompute.fs
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Original file line number Diff line number Diff line change
Expand Up @@ -290,9 +290,13 @@ let rec private preComputeUnionCaseArgInfo (stack : Type list) (helpParam : Help
let dummyFields = types |> Array.map Unchecked.UntypedDefaultOf
caseCtor.Value dummyFields :?> IArgParserTemplate)

// use ref cell for late binding of parent argInfo
let current = ref None
let tryGetCurrent = fun () -> !current
// Late binding of parent argInfo: children captured during construction
// need a back-reference to this `UnionCaseArgInfo`, but we don't have it
// until after we've built `uai` below. Invariant: written exactly once,
// immediately after `uai` is constructed; children read it via the
// `tryGetCurrent` closure.
let mutable current : UnionCaseArgInfo option = None
let tryGetCurrent = fun () -> current

let attributes = lazy uci.GetCustomAttributes()
let declaringTypeAttributes = lazy uci.DeclaringType.GetCustomAttributes(true)
Expand Down Expand Up @@ -540,7 +544,7 @@ let rec private preComputeUnionCaseArgInfo (stack : Type list) (helpParam : Help
IsHidden = isHidden
}

current := Some uai // assign result to children
current <- Some uai // assign result to children
uai

and private preComputeUnionArgInfoInner (stack : Type list) (helpParam : HelpParam option) (tryGetParent : unit -> UnionCaseArgInfo option) (t : Type) : UnionArgInfo =
Expand Down Expand Up @@ -569,9 +573,11 @@ and private preComputeUnionArgInfoInner (stack : Type list) (helpParam : HelpPar

{ Flags = helpSwitches ; Description = description }

// use ref cell for late binding of parent argInfo
let current = ref Unchecked.defaultof<_>
let getCurrent = fun () -> !current
// Late binding of parent argInfo: see comment on the equivalent slot in
// preComputeUnionCaseArgInfo. Invariant: written exactly once at the end
// of this function; children read it via the `getCurrent` closure.
let mutable current : UnionArgInfo = Unchecked.defaultof<_>
let getCurrent = fun () -> current

let caseInfo = lazy(
FSharpType.GetUnionCases(t, allBindings)
Expand Down Expand Up @@ -639,7 +645,7 @@ and private preComputeUnionArgInfoInner (stack : Type list) (helpParam : HelpPar
MainCommandParam = mainCommandParam
}

current := result // assign result to children
current <- result // assign result to children
result

and preComputeUnionArgInfo<'Template when 'Template :> IArgParserTemplate> () =
Expand Down
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