Scala-IO Core: ReadChars and WriteChars

The Input and Output objects of Scala-IO assume that the underlying data is composed of bytes.  However, another common pattern is to have the underlying data be composed of characters instead of bytes, for example java.io.Reader and java.io.Writer.  While it is possible to decompose the output into Bytes and construct an Input object from the decorated object, ReadChars and WriteChars can be used in this situation to reduce the work needed to interact with such resources.

ReadChars and WriteChars are traits that contain the character and string methods of Input and Output.  The primary difference is that the Charset is defined by the underlying resource rather than supplied at the method invocation site.  

Compare two methods:

Input:

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1	def chars(implicit codec: Codec = Codec.default): LongTraversable[Char]

ReadChars:

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1	def chars: LongTraversable[Char]

You will notice that the ReadChars method does not have the codec parameter because there translation is not required, unlike in Input which requires the characters to be created from raw bytes.

Not many examples are needed to explain these concepts but here are a few examples on how to create ReadChar and WriteChar objects:

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import scalax.io._ import JavaConverters._   // JavaConverters has asReadChars and asWriteChars // for converting some objects to ReadChars and WriteChars // (The JavaConverters post will explain // more about the JavaConverters object) "Hello World".asReadChars.chars.size   val writer = new java.io.StringWriter() // Resource object can be used to create a ReadChars and WriteChars val writeChars = Resource.fromWriter(writer).write("Yeee Hawww!") println(Resource.fromReader(new java.io.StringReader(writer.toString)).lines().size)   // ReadChars and WriteChars can be obtained from // InputResource and OutputResource object respectively // SeekableByteChannelResource[SeekableByteChannel] // (returned by fromFile) implements both traits and // therefore has both methods val fileResource = Resource.fromFile("somefile.txt")   implicit val codec = Codec.UTF8 // clear any old data in file fileResource.truncate(0)   // Codec used is declared when calling writer or reader // methods fileResource.writer.write("hi")   println(fileResource.reader.chars.size)