Reverse String

Instructions

Your task is to reverse a given string.

Some examples:

• Turn "stressed" into "desserts".
• Turn "strops" into "sports".
• Turn "racecar" into "racecar".

While there are #reversed and #reverseDo: methods for Strings, can you figure out how to do this yourself using lower level character iteration and streams?

To help you browse code, Pharo has a neat code finder tool. Press Shift-Enter to activate it.

NOTE: We have followed the Exercism convention of calling the solution ReverseString, however a more Smalltalk name would be StringReverser.

Smalltalk and Strings

Concerning strings, there are some obvious little details like double quotes for comments, single quotes for strings, and special syntax for characters (e.g., $x for character “x”) that might confuse you on first reading as the conventions are different from those used by other languages.

There is also the notion of a symbol which is a string that is unique memory-wide; i.e. when it is constructed (typically at compile-time), a memory search is made to determine if another one like it exists; and only the original is used. The rationale is not just memory saving but significant speed-up when comparing symbols.

"this is a comment"
'this is a string'
#'this is a symbol'
#thisIsASymbolToo

There are also very few commas in Smalltalk programs because they play no syntactic role. That’s why array literals, for example, are comma-free; e.g. #(1 2 3 4 5) However, the comma is an operator in its own right and you will notice it when concatenating two strings; e.g. 'string1', 'string2'

Finally, it's worth knowing that Strings and Characters are distinct classes. A String is a collection of Characters. This can catch you off guard when iterating over strings as you can end up giving characters to a method that expects strings. Consider...

(('hello' at: 2) = $e) inspect.
(('hello' at: 2) = 'e') inspect.

Smalltalk and Streams

Streams are useful for sequential reading and writing. They make code cleaner by avoiding the need to increment an index. Streams operate on any collection.

stream := WriteStream on: String new.
stream nextPut: $h ; nextPutAll: 'ell' ; nextPut: $o.
stream contents inspect

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Source

Introductory challenge to reverse an input string