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1
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struct EnumerableDefaultIfEmpty{T,S} <: Enumerable
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2
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23
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source::S
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3
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default_value::T
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4
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end
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5
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6
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0
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Base.eltype(iter::Type{EnumerableDefaultIfEmpty{T,S}}) where {T,S} = T
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7
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8
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0
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_default_value_expr(::Type{T}) where {T} = :( DataValues.DataValue{$T}() )
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9
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10
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23
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_default_value_expr(::Type{T}) where {T<:DataValues.DataValue} = :( $T() )
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11
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12
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function _default_value_expr(::Type{T}) where {T<:NamedTuple}
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13
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23
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return :( NamedTuple{$(fieldnames(T))}( ($( (_default_value_expr(fieldtype(T,i)) for i in 1:length(fieldnames(T)))... ),)) )
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14
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end
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15
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16
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@generated function default_if_empty(source::S) where {S}
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17
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23
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T_source = eltype(source)
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18
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19
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23
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default_value_expr = _default_value_expr(T_source)
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20
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21
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23
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q = quote
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22
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20
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default_value = $default_value_expr
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23
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24
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T = typeof(default_value)
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25
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26
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23
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return EnumerableDefaultIfEmpty{T,$S}(source, default_value)
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27
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end
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28
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29
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23
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return q
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30
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end
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31
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32
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33
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function default_if_empty(source::S, default_value::TD) where {S,TD}
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34
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23
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T = eltype(source)
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35
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if T!=TD
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36
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23
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error("The default value must have the same type as the elements from the source.")
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37
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end
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38
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23
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return EnumerableDefaultIfEmpty{T,S}(source, default_value)
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39
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end
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40
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41
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function Base.iterate(iter::EnumerableDefaultIfEmpty{T,S}) where {T,S}
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42
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23
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s = iterate(iter.source)
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43
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44
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23
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if s===nothing
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45
|
8
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return iter.default_value, nothing
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46
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else
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47
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23
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return convert(T,s[1]), s[2]
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48
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end
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49
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end
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50
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51
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function Base.iterate(iter::EnumerableDefaultIfEmpty{T,S}, state) where {T,S}
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52
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23
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state===nothing && return nothing
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53
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54
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23
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s = iterate(iter.source, state)
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55
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23
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if s===nothing
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56
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23
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return nothing
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57
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else
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58
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23
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return convert(T, s[1]), s[2]
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59
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end
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60
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end
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davidanthoff