My instances provide space-efficient storage of data which tends to be constant over long runs of the possible indices. Essentially repeated values are stored singly and then associated with a "run" length that denotes the number of consecutive occurrences of the value.

My two important variables are
runs An array of how many elements are in each run
values An array of what the value is over those elements

The variables lastIndex, lastRun and lastOffset cache the last access
so that streaming through RunArrays is not an N-squared process.

Many complexities of access can be bypassed by using the method
RunArray withStartStopAndValueDo:

	adding
	addFirst: addLast: addLast:times: coalesce repeatLast:ifEmpty: repeatLastIfEmpty:

	copying
	, copyFrom:to: copyReplaceFrom:to:with:

	enumerating
	runsAndValuesDo:

	printing
	printOn: storeOn: writeOn: writeScanOn:

	private
	at:setRunOffsetAndValue: mapValues: runs setRuns:setValues: values

	accessing	top
	= Test if all my elements are equal to those of otherArray
	at: Primitive. Assumes receiver is indexable. Answer the value of an indexable element in the receiver. Fail if the argument index is not an Integer or is out of bounds. Essential. See Object documentation whatIsAPrimitive.
	first Answer the first element of the receiver. Raise an error if the collection is empty.
	last Answer the last element of the receiver. Raise an error if the collection is empty.
	runLengthAt: Answer the length remaining in run beginning at index.
	size Answer how many elements the receiver contains.
	withStartStopAndValueDo:

	adding	top
	addFirst: Add value as the first element of the receiver.
	addLast: Add value as the last element of the receiver.
	addLast:times: Add value as the last element of the receiver, the given number of times
	coalesce Try to combine adjacent runs
	repeatLast:ifEmpty: add the last value back again, the given number of times. If we are empty, add (defaultBlock value)
	repeatLastIfEmpty: add the last value back again. If we are empty, add (defaultBlock value)

	copying	top
	, Answer a new RunArray that is a concatenation of the receiver and aRunArray.
	copyFrom:to: Answer a copy of a subset of the receiver, starting from element at index start until element at index stop.
	copyReplaceFrom:to:with: Answer a copy of the receiver satisfying the following conditions: If stop is less than start, then this is an insertion; stop should be exactly start-1, start = 1 means insert before the first character, start = size+1 means append after last character. Otherwise, this is a replacement; start and stop have to be within the receiver's bounds.

	enumerating	top
	runsAndValuesDo: Evaluate aBlock with run lengths and values from the receiver

	printing	top
	printOn: Append a sequence of characters that identify the receiver to aStream.
	storeOn: Refer to the comment in Object|storeOn:.
	writeOn: Store the array of bits onto the argument, aStream. (leading byte ~= 16r80) identifies this as raw bits (uncompressed). Always store in Big Endian (Mac) byte order. Do the writing at BitBlt speeds. We only intend this for non-pointer arrays. Do nothing if I contain pointers.
	writeScanOn: Write out the format used for text runs in source files. (14 50 312)f1,f1b,f1LInteger +;i

	private	top
	at:setRunOffsetAndValue: Supply all run information to aBlock.
	mapValues: NOTE: only meaningful to an entire set of runs
	runs
	setRuns:setValues:
	values Answer the values in the receiver.

	instance creation	top
	new Answer a new instance of me, with size = 0.
	new:withAll: Answer a new instance of me, whose every element is equal to the argument, value.
	newFrom: Answer an instance of me containing the same elements as aCollection.
	readFrom: Answer an instance of me as described on the stream, aStream.
	runs:values: Answer an instance of me with runs and values specified by the arguments.
	scanFrom: Read the style section of a fileOut or sources file. nextChunk has already been done. We need to return a RunArray of TextAttributes of various kinds.