2.3: Opening Read and Write Streams

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To open a stream on a file, just ask the reference for a read- or write-stream using the message writeStream or readStream as follows:

| working stream |
working := FileSystem disk workingDirectory.
stream := (working / 'foo.txt') writeStream.
stream nextPutAll: 'Hello World'.
stream close.
stream := (working / 'foo.txt') readStream.
stream contents.    →    'Hello World'
stream close.

Please note that writeStream overrides any existing file and readStream throws an exception if the file does not exist. Forgetting to close stream is a common mistake, for which even advanced programmers regularly fall into. Closing a stream frees low level resources, which is a good thing to do. The messages readStreamDo: and writeStreamDo: frees the programmer from explicitly closing the stream. Consider:

| working |
working := FileSystem disk workingDirectory.
working / 'foo.txt' writeStreamDo: [ :stream | stream nextPutAll: 'Hello World' ].
working / 'foo.txt' readStreamDo: [ :stream | stream contents ].

Keep in mind that file may be easily overridden without giving any warning. Consider the following situation:

| working |
working := FileSystem disk workingDirectory.
working / 'authors.txt' readStreamDo: [ :stream | stream contents ].
    → 'stephane alexandre damien jannik'

The file authors.txt may be simply overridden with:

FileSystem disk workingDirectory / 'authors.txt'
    writeStreamDo: [ :stream | stream nextPutAll: 'bob joe'].

Reading back the file may give an odd result:

| working |
working := FileSystem disk workingDirectory.
working / 'authors.txt' readStreamDo: [ :stream | stream contents ].
    → 'bob joee alexandre damien jannik'

We can also use the message openFilestream: aString writable: aBoolean to get a stream with the corresponding write status.

| stream |
stream := FileSystem disk openFileStream: 'authors.txt' writable: true.
stream nextPutAll: 'stephane alexandre damien jannik'.

Have a look at the streams protocol of FileReference for other convenience methods.