Bug #11381
closedString のサブクラスをハッシュのキーに指定した時に hash メソッドが呼ばれない
Description
String のサブクラスとして大文字小文字を同一視するようなクラスを作ろうとしましたが、
そのオブジェクトをハッシュのキーに指定しても期待通りに動作しませんでした。
どうやら hash メソッドが呼ばれていないようです。
class CIString < String
def eql?(other)
self.casecmp(other) == 0
end
def hash
self.to_s.downcase.hash
end
end
h = {}
k1 = CIString.new("hoge")
k2 = CIString.new("HOGE")
p k1.eql? k2 #=> true
p k1.hash == k2.hash #=> true
h[k1] = 1
h[k2] = 2
p h #=> {"hoge"=>1, "HOGE"=>2}
ちなみに eql? の方はちゃんと呼ばれるようで、次のようにすると同じ値であっても別のキーとみなされます。
class CIString < String
def eql?(other)
false
end
end
h = {}
k1 = CIString.new("hoge")
k2 = CIString.new("hoge")
h[k1] = 1
h[k2] = 2
p h #=> {"hoge"=>1, "hoge"=>2}
次のパッチで期待通りにサブクラスの hash メソッドが呼びだされました。
diff --git a/hash.c b/hash.c
index 7b8733f..26e5a3d 100644
--- a/hash.c
+++ b/hash.c
@@ -145,7 +145,7 @@ rb_any_hash(VALUE a)
}
hnum = rb_objid_hash((st_index_t)a);
}
- else if (BUILTIN_TYPE(a) == T_STRING) {
+ else if (BUILTIN_TYPE(a) == T_STRING && RBASIC(a)->klass == rb_cString) {
hnum = rb_str_hash(a);
}
else if (BUILTIN_TYPE(a) == T_SYMBOL) {
Updated by jeremyevans0 (Jeremy Evans) almost 5 years ago
- Status changed from Open to Feedback
This behavior hasn't changed since the initial report. However, it seems odd to just treat string subclasses (or strings with singleton classes) differently. Currently the behavior is to use C functions for (at least) String, Symbol, Integer, and Float, probably for performance. Your example could apply to someone that wanted to modify the behavior of all strings instead of just a specific string subclass. So I wouldn't consider this an implementation detail, not a bug. There are a lot of cases where Ruby calls C functions instead of Ruby methods internally for performance.
I think you can get something that works fairly well using delegate:
require 'delegate'
class CIString < DelegateClass(String)
def hash
downcase.hash
end
alias to_str __getobj__
alias eql? casecmp?
end
h = {}
k1 = CIString.new("hoge")
k2 = CIString.new("HOGE")
p k1.eql? k2 #=> true
p k1.hash == k2.hash #=> true
h[k1] = 1
h[k2] = 2
p h
# {"hoge"=>2}
Do you think that would work for you?
Updated by jeremyevans0 (Jeremy Evans) over 4 years ago
- Status changed from Feedback to Closed