Bob Sanders said:
Hello. I'm looking to construct a loop that defines an array of [apple,
banana, cherry] like this:
@apple = apple
@banana = banana
@cherry = cherry
I'm thinking it's something in this form:
[apple, banana, cherry].each do |attribute|
@*attribute* = attribute
end
..but I have no idea what belongs in place of the *attribute*. Does
anyone know?
Yes. The objects in ruby do know if and when, how. You must ask them!
For example, using ri(1).
irb(main):001:0> (ri "Object")
---------------------------------------------------------- Class: Object
+Object+ is the parent class of all classes in Ruby. Its methods
are therefore available to all objects unless explicitly
overridden.
+Object+ mixes in the +Kernel+ module, making the built-in kernel
functions globally accessible. Although the instance methods of
+Object+ are defined by the +Kernel+ module, we have chosen to
document them here for clarity.
In the descriptions of Object's methods, the parameter _symbol_
refers to a symbol, which is either a quoted string or a +Symbol+
(such as +:name+).
------------------------------------------------------------------------
Includes:
---------
Kernel(Array, Float, Integer, Pathname, String, URI, `, abort,
at_exit, autoload, autoload?, binding, block_given?, callcc,
caller, catch, chomp, chomp!, chop, chop!, eval, exec, exit, exit!,
fail, fork, format, getc, gets, global_variables, gsub, gsub!,
iterator?, lambda, load, local_variables, loop, method_missing,
open, open, open_uri_original_open, p, pp, pretty_inspect, print,
printf, proc, putc, puts, raise, rand, readline, readlines,
require, scan, scanf, select, set_trace_func, sleep, split,
sprintf, srand, sub, sub!, syscall, system, test, throw, trace_var,
trap, untrace_var, warn, warn, y), PP::ObjectMixin(pretty_print,
pretty_print_cycle, pretty_print_inspect,
pretty_print_instance_variables)
Constants:
----------
MatchingData: rb_cMatch
ENV: envtbl
ENV: envtbl
TOPLEVEL_BINDING: rb_f_binding(ruby_top_self)
STDIN: rb_stdin
STDOUT: rb_stdout
STDERR: rb_stderr
ARGF: argf
NIL: Qnil
TRUE: Qtrue
FALSE: Qfalse
DATA: f
ARGV: rb_argv
RUBY_VERSION: v
RUBY_RELEASE_DATE: d
RUBY_PLATFORM: p
RUBY_PATCHLEVEL: INT2FIX(RUBY_PATCHLEVEL)
VERSION: v
RELEASE_DATE: d
PLATFORM: p
IPsocket: rb_cIPSocket
TCPsocket: rb_cTCPSocket
SOCKSsocket: rb_cSOCKSSocket
TCPserver: rb_cTCPServer
UDPsocket: rb_cUDPSocket
UNIXsocket: rb_cUNIXSocket
UNIXserver: rb_cUNIXServer
Class methods:
--------------
new
Instance methods:
-----------------
==, ===, =~, __id__, __send__, class, clone, dclone, display, dup,
enum_for, eql?, equal?, extend, freeze, frozen?, hash, id, inspect,
instance_eval, instance_of?, instance_variable_get,
instance_variable_get, instance_variable_set,
instance_variable_set, instance_variables, is_a?, kind_of?, method,
methods, nil?, object_id, private_methods, protected_methods,
public_methods, remove_instance_variable, respond_to?, send,
singleton_method_added, singleton_method_removed,
singleton_method_undefined, singleton_methods, taint, tainted?,
to_a, to_enum, to_s, to_yaml, to_yaml_properties, to_yaml_style,
type, untaint
nil
irb(main):002:0> (ri "Object.instance_variable_set")
------------------------------------------- Object#instance_variable_set
obj.instance_variable_set(symbol, obj) => obj
------------------------------------------------------------------------
Sets the instance variable names by _symbol_ to _object_, thereby
frustrating the efforts of the class's author to attempt to provide
proper encapsulation. The variable did not have to exist prior to
this call.
class Fred
def initialize(p1, p2)
@a, @b = p1, p2
end
end
fred = Fred.new('cat', 99)
fred.instance_variable_set
@a, 'dog') #=> "dog"
fred.instance_variable_set
@c, 'cat') #=> "cat"
fred.inspect #=> "#<Fred:0x401b3da8 @a=\"dog\", @b=99, @c=\"cat\">"
nil
irb(main):003:0> ( ["apple","banana","cherry"] . each { | attribute | (self . instance_variable_set( (("@" + attribute) . to_sym) , attribute)) } )
["apple", "banana", "cherry"]
irb(main):004:0> @apple
"apple"
irb(main):005:0> @banana
"banana"
irb(main):006:0> @cherry
"cherry"
irb(main):007:0> @pear
nil
irb(main):008:0>
That said, an array like [apple, banana, cherry] will actually be an
array such as ["value of apple", 42, ["the",:value,0,"cherry"]].
If you want to build an array containing the name of the variable,
then you have to make an array of symbols:
[:apple,:banana,:cherry].
Then you will have to write:
irb(main):018:0> (begin
(apple = "value of apple")
(banana = 42)
(cherry = ["the",:value,0,"cherry"])
( [:apple,:banana,:cherry] . each { | variable | (self . instance_variable_set( (("@" + (variable . to_s)) . to_sym) ,
(eval (variable . to_s)))) })
end)
[:apple, :banana, :cherry]
irb(main):025:0> @apple
"value of apple"
irb(main):026:0> @banana
42
irb(main):027:0> @cherry
["the", :value, 0, "cherry"]
irb(main):028:0>
