39 lines
868 B
Crystal
39 lines
868 B
Crystal
module DB
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# :nodoc:
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struct EnumerableConcat(S, T, U)
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include Enumerable(S)
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def initialize(@e1 : T, @e2 : U)
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end
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def each
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if e1 = @e1
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@e1.each do |e|
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yield e
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end
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end
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if e2 = @e2
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e2.each do |e|
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yield e
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end
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end
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end
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# returns given `e1 : T` an `Enumerable(T')` and `e2 : U` an `Enumerable(U') | Nil`
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# it returns an `Enumerable(T' | U')` that enumerates the elements of `e1`
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# and, later, the elements of `e2`.
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def self.build(e1 : T, e2 : U)
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return e1 if e2.nil? || e2.empty?
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return e2 if e1.nil? || e1.empty?
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EnumerableConcat(Union(typeof(sample(e1)), typeof(sample(e2))), T, U).new(e1, e2)
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end
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private def self.sample(c : Enumerable?)
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c.not_nil!.each do |e|
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return e
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end
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raise ""
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end
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end
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end
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