Create an object/Native demonstration: Difference between revisions
(→{{header|Ruby}}: Add some important parts (lFencedHash#delete, FencedHash#store).) |
(→{{header|Ruby}}: Add more tests. Implement FencedHash#clone, FencedHash#dup and FencedHash#freeze.) |
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<lang ruby># fencedhash.rb |
<lang ruby># fencedhash.rb |
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require 'forwardable' |
require 'forwardable' |
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unless defined? KeyError |
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KeyError = IndexError |
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end |
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# A FencedHash acts like a Hash, but with a fence around its keys. |
# A FencedHash acts like a Hash, but with a fence around its keys. |
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:rassoc, :size, :to_a, :values, :values_at) |
:rassoc, :size, :to_a, :values, :values_at) |
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attr_reader :default_proc |
attr_reader :default_proc |
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# TODO: This causes test_each_rewind to fail! |
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def_delegators :@hash, :each |
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# Acts like Hash::[] but creates a FencedHash. |
# Acts like Hash::[] but creates a FencedHash. |
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raise ArgumentError, "wrong number of arguments" |
raise ArgumentError, "wrong number of arguments" |
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end |
end |
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super() |
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if block_given? |
if block_given? |
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args.first.each { |key| @hash[key] = @hash[key] } |
args.first.each { |key| @hash[key] = @hash[key] } |
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end |
end |
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end |
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def initialize_copy(orig) |
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super |
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@hash = @hash.dup |
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end |
end |
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# but resets the value to default. |
# but resets the value to default. |
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def clear |
def clear |
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@hash = @hash |
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@hash.each_key { |key| delete key } |
@hash.each_key { |key| delete key } |
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self |
self |
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# ..... |
# ..... |
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def default_proc=(proc_obj) |
def default_proc=(proc_obj) |
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@hash = @hash |
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# Convert _proc_obj_ to a block parameter. |
# Convert _proc_obj_ to a block parameter. |
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proc_obj = proc &proc_obj |
proc_obj = proc &proc_obj |
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# If _key_ is in the fence..... |
# If _key_ is in the fence..... |
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def delete(key) |
def delete(key) |
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@hash = @hash |
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begin |
begin |
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original_value = @hash.fetch(key) |
original_value = @hash.fetch(key) |
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rescue |
rescue IndexError |
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# _key_ is not in the fence. |
# _key_ is not in the fence. |
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if block_given? |
if block_given? |
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# not in the fence, then this method raises KeyError. |
# not in the fence, then this method raises KeyError. |
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def store(key, value) |
def store(key, value) |
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@hash = @hash |
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if @hash.has_key? key |
if @hash.has_key? key |
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@hash.store(key, value) |
@hash.store(key, value) |
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else |
else |
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c = if defined? KeyError; then KeyError; else IndexError; end |
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raise c, "fence prevents new key: #{key}" |
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end |
end |
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end |
end |
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class TestFencedHash < Test::Unit::TestCase |
class TestFencedHash < Test::Unit::TestCase |
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if RUBY_VERSION >= "1.9" |
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KeyEx = KeyError |
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FrozenEx = RuntimeError |
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else |
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KeyEx = IndexError |
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FrozenEx = TypeError |
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end |
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def setup |
def setup |
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@fh = FencedHash[:q => 11, :w => 22, :e => 33, |
@fh = FencedHash[:q => 11, :w => 22, :e => 33, |
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assert_equal 55, @fh[:t] |
assert_equal 55, @fh[:t] |
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assert_equal 66, @fh[:y] |
assert_equal 66, @fh[:y] |
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assert_nil @fh[ |
assert_nil @fh[:u] |
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end |
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def test_delete |
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assert_equal 44, (@fh.delete :r) |
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assert_nil @fh.fetch(:r) |
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assert_nil @fh.delete(:r) |
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assert_nil @fh.delete(:u) |
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@fh[:r] = "replacement" |
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assert_equal "replacement", (@fh.delete :r) |
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end |
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def test_delete_if |
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a = @fh.delete_if { |key, value| key == :t || value == 66 } |
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assert_same @fh, a |
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assert_equal 4, @fh.length |
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@fh[:y] = "why?" |
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@fh[:t] = "tee!" |
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assert_equal 6, @fh.length |
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end |
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def test_each |
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count = 0 |
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@fh.each do |key, value| |
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assert_kind_of Symbol, key |
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assert_kind_of Integer, value |
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assert_equal true, (@fh.has_key? key) |
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assert_equal true, (@fh.has_value? value) |
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count += 1 |
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end |
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assert_equal 6, count |
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end |
end |
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assert_equal 55, @fh.fetch(:t) |
assert_equal 55, @fh.fetch(:t) |
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assert_equal 66, @fh.fetch(:y) |
assert_equal 66, @fh.fetch(:y) |
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assert_raises( |
assert_raises(KeyEx) { @fh.fetch :u } |
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end |
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def test_freeze |
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assert_equal false, @fh.frozen? |
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@fh.freeze |
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2.times do |
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assert_equal true, @fh.frozen? |
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assert_raises(FrozenEx) { @fh.clear } |
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assert_raises(FrozenEx) { @fh.delete :q } |
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assert_raises(FrozenEx) { @fh.store :w, "different" } |
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assert_raises(FrozenEx) { @fh[:w] = "different" } |
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# Repeat the tests with a clone. The clone must be frozen. |
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@fh = @fh.clone |
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end |
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# A duplicate is not frozen. |
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@fh = @fh.dup |
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assert_equal false, @fh.frozen? |
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@fh[:w] = "different" |
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assert_equal "different", @fh[:w] |
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end |
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def test_has_key |
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2.times do |t| |
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assert_equal true, (@fh.has_key? :y) |
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assert_equal true, (@fh.include? :y) |
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assert_equal true, (@fh.key? :y) |
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assert_equal true, (@fh.member? :y) |
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assert_equal false, (@fh.has_key? :u) |
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assert_equal false, (@fh.include? :u) |
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assert_equal false, (@fh.key? :u) |
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assert_equal false, (@fh.member? :u) |
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# Repeat the tests. |
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# The fence must prevent any changes to the keys. |
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@fh.delete :y |
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(@fh[:u] = "value") rescue "ok" |
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end |
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end |
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def test_inject |
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# To get an :inject method, FencedHash should mix in Enumerable. |
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assert_kind_of Enumerable, @fh |
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assert_equal 231, @fh.inject(0) { |sum, kv| sum + kv[1] } |
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end |
end |
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def test_keys |
def test_keys |
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assert_equal([:e, :q, :r, :t, :w, :y], |
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sort = proc { |a| a.sort_by { |o| o.to_s }} |
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@fh.keys.sort_by { |o| o.to_s }) |
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end |
end |
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assert_equal 6, @fh.length |
assert_equal 6, @fh.length |
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assert_equal 6, @fh.size |
assert_equal 6, @fh.size |
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end |
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def test_store |
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assert_raises(KeyEx) { @fh[:a] = 111 } |
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assert_equal 222, (@fh[:e] = 222) |
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assert_equal 222, (@fh.fetch :e) |
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assert_equal 333, @fh.store(:e, 333) |
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assert_equal 333, @fh[:e] |
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end |
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def test_values |
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assert_equal [11, 22, 33, 44, 55, 66], @fh.values.sort! |
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end |
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if RUBY_VERSION >= "1.8.7" |
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def test_delete_if_enum |
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a = @fh.delete_if.with_index { |kv, i| i >= 2 } |
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assert_same @fh, a |
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assert_equal 2, @fh.length |
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end |
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end |
end |
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if RUBY_VERSION >= "1.9" |
if RUBY_VERSION >= "1.9" |
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def test_each_rewind |
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class << @fh |
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attr_reader :test_rewind |
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def rewind |
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@test_rewind = "correct" |
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end |
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end |
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assert_nil @fh.test_rewind |
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# @fh.each.rewind must call @fh.rewind. If @fh forwards :each |
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# to another object then this test fails. |
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@fh.each.rewind |
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assert_equal "correct", @fh.test_rewind |
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end |
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def test_insertion_order |
def test_insertion_order |
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assert_equal [:q, :w, :e, :r, :t, :y], @fh.keys |
assert_equal [:q, :w, :e, :r, :t, :y], @fh.keys |
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assert_equal [11, 22, 33, 44, 55, 66], @fh.values |
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end |
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def test_key |
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assert_equal :q, @fh.key(11) |
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assert_equal :w, @fh.key(22) |
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assert_equal :e, @fh.key(33) |
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assert_equal :r, @fh.key(44) |
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assert_equal :t, @fh.key(55) |
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assert_equal :y, @fh.key(66) |
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assert_nil @fh.key(77) |
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end |
end |
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end |
end |
Revision as of 21:28, 16 February 2011
Task:
Create a Hash/Associative Array/Dictionary-like object, which is initialized with some default key/value pairs. The object should behave like a native Hash/Associative Array/Dictionary of the language, if any, but with the following differences:
- No new item can be added;
- Item cannot be deleted, (but native delete method may used to reset the item's value to default) ;
Objective:
The objective is not just create such object, but to demonstarion the language's native way of object creation. For some language, the task should show how the so-called Magic Methods work.
J
Given a list of keys and an associated list of values, the idiomatic way of expressing this concept in J would be:
<lang j>lookup=: values {~ keys&i.</lang>
For example:
<lang j> lookup=: 10 20 30 40 50 {~ (;:'this is a test')&i.
lookup ;:'a test'
30 40</lang>
Notes:
1) While the result can not be modified or deleted, the name used to refer to it can be made to refer to something else, and once all references are lost it will be garbage collected.
2) In the above example, we have 5 values and 4 keys. The extra value is used when no key is found. If no extra value was provided, the "key not found" case would be an error case.
3) In J, objects are always referenced, but all data is passed by value. This means that objects can never be passed to a function -- only a reference to an object (its name) can be passed. This means that objects exist only in the way things are named, in J. So for the most part, we do not call things "objects" in J, and this task has nothing to do with what are called "objects" in J. However, this does demonstrate how things are created in J -- you write their definition, and can use them and/or assign to names or inspect them or whatever else.
JavaScript
This is a first demonstration of the task, but only implemented the functionality, not any native behavior, eg indexing. JavaScript experts may want to replace this one.
<lang javascript>var keyError = new Error("Invalid Key Error (FixedKeyDict)") ;
function FixedKeyDict(obj) {
var myDefault = new Object() ; var myData = new Object() ; for(k in obj) { myDefault[k] = obj[k] ; myData[k] = obj[k] ; }
var gotKey = function(k) { for(kk in myDefault) { if(kk == k) return true ; } return false ; } ;
this.hasKey = gotKey ;
var checkKey = function(k) { if(!gotKey(k)) throw keyError ; } ; this.getItem = function(k) { checkKey(k) ; return myData[k]; } ; this.setItem = function(k, v) { checkKey(k) ; myData[k] = v ; } ; this.resetItem = function(k) { checkKey(k) ; myData[k] = myDefault[k] ; } ; this.delItem = this.resetItem ; this.clear = function() { for(k in myDefault) myData[k] = myDefault[k] ; } ; this.iterator = function() { for(k in myDefault) yield (k); } ; this.clone = function() { return new FixedKeyDict(myDefault) ; } this.toStr = function() { var s = "" ; for(key in myData) s = s + key + " => " + myData[key] + ", " ; return "FixedKeyDict{" + s + "}" ; } ;
}</lang>
Test run:
<lang javascript>
const BR = "
\n"
var pl = function(s) {
document.write(s + BR) ;
} ;
pl("
") ; var o = { foo:101, bar:102 } ; var h = new FixedKeyDict(o) ; pl("Fixed Key Dict Created") ; pl("toString : " + h.toStr()) ; pl("get an item: " + h.getItem("foo")) ; pl("check a key: " + h.hasKey("boo")) ; pl("ditto : " + h.hasKey("bar")) ; h.setItem("bar", 999) ; pl("set an item: " + h.toStr()) ; pl("Test iterator (or whatever)") ; for(k in h.iterator()) pl(" " + k + " => " + h.getItem(k)) ; var g = h.clone() ; pl("Clone a dict") ; pl(" clone : " + g.toStr()) ; pl(" original : " + h.toStr()) ; h.clear() ; pl("clear or reset the dict") ; pl(" : " + h.toStr()) ; try { h.setItem("NoNewKey", 666 ) ; } catch(e) { pl("error test : " + e.message) ; } </lang> output : <pre> Fixed Key Dict Created toString : FixedKeyDict{foo => 101, bar => 102, } get an item: 101 check a key: false ditto : true set an item: FixedKeyDict{foo => 101, bar => 999, } Test iterator (or whatever) foo => 101 bar => 999 Clone a dict clone : FixedKeyDict{foo => 101, bar => 102, } original : FixedKeyDict{foo => 101, bar => 999, } clear or reset the dict : FixedKeyDict{foo => 101, bar => 102, } error test : Invalid Key Error (FixedKeyDict)
Ruby
TODO: Add missing methods (FencedHash#delete_if). Write missing comments. Do more tests.
<lang ruby># fencedhash.rb require 'forwardable'
- A FencedHash acts like a Hash, but with a fence around its keys.
- After the creation of a FencedHash, one cannot add nor remove keys.
- Any attempt to insert a new key will raise KeyError. Any attempt to
- delete a key-value pair will keep the key but will reset the value to
- the default value.
class FencedHash < Object
extend Forwardable include Enumerable
#-- # @hash: our Hash inside the fence # @default_proc: passes self, not @hash #++ def_delegators(:@hash, :[], :assoc, :compare_by_identity, :compare_by_identity?, :default, :empty?, :fetch, :flatten, :has_key?, :has_value?, :hash, :include?, :key, :key?, :keys, :length, :member?, :rassoc, :size, :to_a, :values, :values_at) attr_reader :default_proc
# TODO: This causes test_each_rewind to fail! def_delegators :@hash, :each
# Acts like Hash::[] but creates a FencedHash. def self.[](*args) FencedHash.allocate.instance_eval do @hash = Hash[*args] self end end
# call-seq: # FencedHash.new(obj=nil [,keys]) -> fh # FencedHash.new([keys]) { |fh, key| block } -> fh # # Creates a FencedHash..... def initialize(*args, &block) if arguments.length > (block_given? && 1 || 2) raise ArgumentError, "wrong number of arguments" end
if block_given? @default_proc = block @hash = Hash.new { |hash, key| yield self, key } else # FencedHash.new() acts like FencedHash.new(nil) because # if args.empty?, then args.shift returns nil. @hash = Hash.new(args.shift) end
# For all keys in the fence, insert their default values. unless args.empty? args.first.each { |key| @hash[key] = @hash[key] } end end
def initialize_copy(orig) super @hash = @hash.dup end
# Clears all values. For each key-value pair, this retains the key # but resets the value to default. def clear @hash = @hash @hash.each_key { |key| delete key } self end
# ..... def default=(obj) @default_proc = nil @hash.default = obj end
# ..... def default_proc=(proc_obj) @hash = @hash
# Convert _proc_obj_ to a block parameter. proc_obj = proc &proc_obj
@hash.default_proc = proc { |hash, key| proc_obj[self, key] } @default_proc = proc_obj end
# Deletes the value of the key-value pair for _key_. # # If _key_ is in the fence..... def delete(key) @hash = @hash
begin original_value = @hash.fetch(key) rescue IndexError # _key_ is not in the fence. if block_given? yield key else @hash[key] end else # _key_ is in the fence. Must reset the value. From Ruby 1.9, # @hash remembers the insertion order of the keys. Must preserve # this insertion order and must not call @hash.delete(key). default = if @default_proc @default_proc[self, key] else @hash.default end @hash.store(key, default) original_value end end
# Stores a _value_ for a _key_. This only works if _key_ is in the # fence; FencedHash prevents the insertion of new keys. If _key_ is # not in the fence, then this method raises KeyError. def store(key, value) @hash = @hash if @hash.has_key? key @hash.store(key, value) else c = if defined? KeyError; then KeyError; else IndexError; end raise c, "fence prevents new key: #{key}" end end alias []= store
end</lang>
<lang ruby># fh-test.rb require 'fencedhash' require 'test/unit'
class TestFencedHash < Test::Unit::TestCase
if RUBY_VERSION >= "1.9" KeyEx = KeyError FrozenEx = RuntimeError else KeyEx = IndexError FrozenEx = TypeError end
def setup @fh = FencedHash[:q => 11, :w => 22, :e => 33, :r => 44, :t => 55, :y => 66] end
def test_bracket_operator assert_equal 11, @fh[:q] assert_equal 22, @fh[:w] assert_equal 33, @fh[:e] assert_equal 44, @fh[:r] assert_equal 55, @fh[:t] assert_equal 66, @fh[:y] assert_nil @fh[:u] end
def test_delete assert_equal 44, (@fh.delete :r) assert_nil @fh.fetch(:r) assert_nil @fh.delete(:r) assert_nil @fh.delete(:u) @fh[:r] = "replacement" assert_equal "replacement", (@fh.delete :r) end
def test_delete_if a = @fh.delete_if { |key, value| key == :t || value == 66 } assert_same @fh, a assert_equal 4, @fh.length @fh[:y] = "why?" @fh[:t] = "tee!" assert_equal 6, @fh.length end
def test_each count = 0 @fh.each do |key, value| assert_kind_of Symbol, key assert_kind_of Integer, value assert_equal true, (@fh.has_key? key) assert_equal true, (@fh.has_value? value) count += 1 end assert_equal 6, count end
def test_fetch assert_equal 11, @fh.fetch(:q) assert_equal 22, @fh.fetch(:w) assert_equal 33, @fh.fetch(:e) assert_equal 44, @fh.fetch(:r) assert_equal 55, @fh.fetch(:t) assert_equal 66, @fh.fetch(:y) assert_raises(KeyEx) { @fh.fetch :u } end
def test_freeze assert_equal false, @fh.frozen? @fh.freeze
2.times do assert_equal true, @fh.frozen? assert_raises(FrozenEx) { @fh.clear } assert_raises(FrozenEx) { @fh.delete :q } assert_raises(FrozenEx) { @fh.store :w, "different" } assert_raises(FrozenEx) { @fh[:w] = "different" }
# Repeat the tests with a clone. The clone must be frozen. @fh = @fh.clone end
# A duplicate is not frozen. @fh = @fh.dup assert_equal false, @fh.frozen? @fh[:w] = "different" assert_equal "different", @fh[:w] end
def test_has_key 2.times do |t| assert_equal true, (@fh.has_key? :y) assert_equal true, (@fh.include? :y) assert_equal true, (@fh.key? :y) assert_equal true, (@fh.member? :y)
assert_equal false, (@fh.has_key? :u) assert_equal false, (@fh.include? :u) assert_equal false, (@fh.key? :u) assert_equal false, (@fh.member? :u)
# Repeat the tests. # The fence must prevent any changes to the keys. @fh.delete :y (@fh[:u] = "value") rescue "ok" end end
def test_inject # To get an :inject method, FencedHash should mix in Enumerable. assert_kind_of Enumerable, @fh assert_equal 231, @fh.inject(0) { |sum, kv| sum + kv[1] } end
def test_keys assert_equal([:e, :q, :r, :t, :w, :y], @fh.keys.sort_by { |o| o.to_s }) end
def test_length assert_equal 6, @fh.length assert_equal 6, @fh.size end
def test_store assert_raises(KeyEx) { @fh[:a] = 111 } assert_equal 222, (@fh[:e] = 222) assert_equal 222, (@fh.fetch :e) assert_equal 333, @fh.store(:e, 333) assert_equal 333, @fh[:e] end
def test_values assert_equal [11, 22, 33, 44, 55, 66], @fh.values.sort! end
if RUBY_VERSION >= "1.8.7" def test_delete_if_enum a = @fh.delete_if.with_index { |kv, i| i >= 2 } assert_same @fh, a assert_equal 2, @fh.length end end
if RUBY_VERSION >= "1.9" def test_each_rewind class << @fh attr_reader :test_rewind def rewind @test_rewind = "correct" end end assert_nil @fh.test_rewind
# @fh.each.rewind must call @fh.rewind. If @fh forwards :each # to another object then this test fails. @fh.each.rewind assert_equal "correct", @fh.test_rewind end
def test_insertion_order assert_equal [:q, :w, :e, :r, :t, :y], @fh.keys assert_equal [11, 22, 33, 44, 55, 66], @fh.values end
def test_key assert_equal :q, @fh.key(11) assert_equal :w, @fh.key(22) assert_equal :e, @fh.key(33) assert_equal :r, @fh.key(44) assert_equal :t, @fh.key(55) assert_equal :y, @fh.key(66) assert_nil @fh.key(77) end end
end</lang>