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#
#
# Nim's Runtime Library
# (c) Copyright 2020 Nim contributors
#
# See the file "copying.txt", included in this
# distribution, for details about the copyright.
#
import macros
macro genEnumCaseStmt*(typ: typedesc, argSym: typed, default: typed,
userMin, userMax: static[int], normalizer: static[proc(s :string): string]): untyped =
# generates a case stmt, which assigns the correct enum field given
# a normalized string comparison to the `argSym` input.
# string normalization is done using passed normalizer.
# NOTE: for an enum with fields Foo, Bar, ... we cannot generate
# `of "Foo".nimIdentNormalize: Foo`.
# This will fail, if the enum is not defined at top level (e.g. in a block).
# Thus we check for the field value of the (possible holed enum) and convert
# the integer value to the generic argument `typ`.
let typ = typ.getTypeInst[1]
let impl = typ.getImpl[2]
expectKind impl, nnkEnumTy
let normalizerNode = quote: `normalizer`
expectKind normalizerNode, nnkSym
result = nnkCaseStmt.newTree(newCall(normalizerNode, argSym))
# stores all processed field strings to give error msg for ambiguous enums
var foundFields: seq[string] = @[]
var fStr = "" # string of current field
var fNum = BiggestInt(0) # int value of current field
for f in impl:
case f.kind
of nnkEmpty: continue # skip first node of `enumTy`
of nnkSym, nnkIdent: fStr = f.strVal
of nnkEnumFieldDef:
case f[1].kind
of nnkStrLit: fStr = f[1].strVal
of nnkTupleConstr:
fStr = f[1][1].strVal
fNum = f[1][0].intVal
of nnkIntLit:
fStr = f[0].strVal
fNum = f[1].intVal
else: error("Invalid tuple syntax!", f[1])
else: error("Invalid node for enum type!", f)
# add field if string not already added
if fNum >= userMin and fNum <= userMax:
fStr = normalizer(fStr)
if fStr notin foundFields:
result.add nnkOfBranch.newTree(newLit fStr, nnkCall.newTree(typ, newLit fNum))
foundFields.add fStr
else:
error("Ambiguous enums cannot be parsed, field " & $fStr &
" appears multiple times!", f)
inc fNum
# finally add else branch to raise or use default
if default == nil:
let raiseStmt = quote do:
raise newException(ValueError, "Invalid enum value: " & $`argSym`)
result.add nnkElse.newTree(raiseStmt)
else:
expectKind(default, nnkSym)
result.add nnkElse.newTree(default)
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