Characters, Strings and Symbols

What You Will Learn

• Characters
• Strings: a collection of characters
• Symbols: unique strings

Characters

• Characters:
  • $F, $Q $U $E $N $T $i $N
• Unprintable characters:
  • Character space, Character tab, Character cr

'Strings'

Delimited by '

'eclair au chocolat'	

'eclair au chocolat' size
> 18

Character space split: 'eclair au chocolat' 
> an OrderedCollection('eclair' 'au' 'chocolat')	

A String: a Collection of Characters

'eclair au chocolat' at: 1
> $e

'eclair au chocolat' do: [:each | Transcript show: each ; cr ]

Quote in Strings

• To add a quote in a string with just type it twice

'L''eclair au chocolat' 

• Pay attention there is only one element

'L''eclair au chocolat' at: 2
> $'

'L''eclair au chocolat' at: 3
> $e

Getting the Last Char

| str |
str := 'Tiramisu'.
str at: str size
> $u

str last
> $u

Ways to Obtain a String

#mac asString
> 'mac'

12 printString
>'12'

String with: $A

For Concatenation Use ,

'Calvin' , ' & ', 'Hobbes'
> 'Calvin & Hobbes'

Take Care With ,

Message comma #, copies strings so multiple concatenations can generate useless intermediate versions

'Calvin' , ' & ', 'Hobbes'
> 'Calvin & Hobbes'

• Benchmark it
• If this is worth, use a stream to avoid creating multiple intermediary strings

String streamContents: [ :s |
   s 
     nextPutAll: 'Calvin';
     nextPutAll: ' & ';
     nextPutAll: 'Hobbes' ]

Symbols

• #calvin is a symbol
• A kind of string
• Unique in the system
• Starts with #
  • #class #mac #at:put: #+ #accept:

Symbols are Unique

Two symbols with the same representation points to the same object

#calvin == #calvin
> true 

Two strings with the same representation may be different objects depending on compiler optimisations

Symbols vs. Strings

• A symbol is a read-only and unique object
• A string is a mutable object (for now)
• Symbols are used as method selectors
• Symbols are good candidates for identity based dictionaries (IdentityDictionary)

What You Should Know

• Strings are collections of characters
• Symbols are unique immutable strings