49 lines
1.6 KiB
Plaintext
49 lines
1.6 KiB
Plaintext
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There are two types of sequence and stream operations:
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* Intermediate operations, which return another sequence or stream
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* Terminal operations, which return something else
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Intermediate operations are lazy, meaning they aren't actually executed until and unless a terminal sequence operation
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is performed on their results. Consequently, if the result of an intermediate sequence operation is not fed to a
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terminal operation, it serves no purpose, which is almost certainly an error.
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== Noncompliant Code Example
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[source,kotlin]
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----
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val sequence = sequenceOf("Hello", " ", "World")
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var totalLength = 0
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sequence.map { totalLength += it.length } // Noncompliant, do nothing, "map" is not a terminal operation
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// here totalLength == 0
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----
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[source,kotlin]
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----
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val stream = listOf("Hello", " ", "World").stream()
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stream.filter { it.isNotBlank() } // Noncompliant, do nothing, "filter" is not a terminal operation
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// the following "forEach" throws an exception, only one method can operate on a stream instance
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// here "filter" has already operated on it.
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stream.forEach { println(it) }
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----
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== Compliant Solution
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[source,kotlin]
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----
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val sequence = listOf("Hello", " ", "World").asSequence()
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var totalLength = sequence.map { it.length }.sum() // Compliant, the sequence ends with the terminal operation "sum"
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// here totalLength == 11
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----
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[source,kotlin]
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----
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listOf("Hello", " ", "World").stream()
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.filter { it.isNotBlank() }
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.forEach { println(it) } // Compliant, the stream ends with the terminal operation "forEach"
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----
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== See
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* https://kotlinlang.org/docs/sequences.html#sequence-operations[Sequence operations]
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