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Welcome to Scala version 2.10.0-RC3 (OpenJDK64-BitServerVM, Java1.7.0_09).
Type in expressions to have them evaluated.
Type:help for more information.
scala>varname="foo"+1
name:String= foo1
scala>vars1=Symbol(name)
s1:Symbol='foo1
scala> s1 =null
s1:Symbol=null
scala>System.gc
scala>vals2=Symbol("foo1")
s2:Symbol='foo1
scala> name =null
name:String=null
scala>System.gc
scala>vals3=Symbol("foo1")
s3:Symbol='foo1
scala> s2 eq s3
res2:Boolean=false
The problem arises if the symbol object for a particular name is garbage collected (so the weak reference stored in Symbol's weak hash map is null), but the string for that name has not been garbage collected (so the key still exists in the weak hash map). If a new symbol object with the same name is added, the weak hash map key will be a different object from the name field of the symbol object. If that string is subsequently garbage collected, the weak hash map entry disappears, so if the symbol is then created for a third time, it will end up being a different object from the second one.
See the following REPL session:
The problem arises if the symbol object for a particular name is garbage collected (so the weak reference stored in
Symbol
's weak hash map is null), but the string for that name has not been garbage collected (so the key still exists in the weak hash map). If a new symbol object with the same name is added, the weak hash map key will be a different object from the name field of the symbol object. If that string is subsequently garbage collected, the weak hash map entry disappears, so if the symbol is then created for a third time, it will end up being a different object from the second one.For additional background, see https://groups.google.com/d/topic/scala-user/mp_pSbfRECI/discussion
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