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| System.Mem.StableName | | Portability | non-portable | | Stability | experimental | | Maintainer | libraries@haskell.org |
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| Contents |
- Stable Names
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| Description |
Stable names are a way of performing fast (O(1)), not-quite-exact
comparison between objects. Stable names solve the following problem: suppose you want to build
a hash table with Haskell objects as keys, but you want to use
pointer equality for comparison; maybe because the keys are large
and hashing would be slow, or perhaps because the keys are infinite
in size. We can't build a hash table using the address of the
object as the key, because objects get moved around by the garbage
collector, meaning a re-hash would be necessary after every garbage
collection.
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| Synopsis |
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| Stable Names |
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| data StableName a |
An abstract name for an object, that supports equality and hashing. Stable names have the following property: - If sn1 :: StableName and sn2 :: StableName and sn1 == sn2
then sn1 and sn2 were created by calls to makeStableName on
the same object.
The reverse is not necessarily true: if two stable names are not
equal, then the objects they name may still be equal. Stable Names are similar to Stable Pointers (StablePtr),
but differ in the following ways: - There is no freeStableName operation, unlike StablePtrs.
Stable names are reclaimed by the runtime system when they are no
longer needed.
- There is no deRefStableName operation. You can't get back from
a stable name to the original Haskell object. The reason for
this is that the existence of a stable name for an object does not
guarantee the existence of the object itself; it can still be garbage
collected.
| | Instances | |
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| makeStableName :: a -> IO (StableName a) |
| Makes a StableName for an arbitrary object. The object passed as
the first argument is not evaluated by makeStableName. |
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| hashStableName :: StableName a -> Int |
| Convert a StableName to an Int. The Int returned is not
necessarily unique; several StableNames may map to the same Int
(in practice however, the chances of this are small, so the result
of hashStableName makes a good hash key). |
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| Produced by Haddock version 0.4 |
