| Copyright | (c) The University of Glasgow 2001 |
|---|---|
| License | BSD-style (see the file libraries/base/LICENSE) |
| Maintainer | [email protected] |
| Stability | experimental |
| Portability | non-portable |
| Safe Haskell | Trustworthy |
| Language | Haskell2010 |
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.
data StableName a Source
An abstract name for an object, that supports equality and hashing.
Stable names have the following property:
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. Note in particular that mkStableName may return a different StableName after an object is evaluated.
Stable Names are similar to Stable Pointers (Foreign.StablePtr), but differ in the following ways:
freeStableName operation, unlike Foreign.StablePtrs. Stable names are reclaimed by the runtime system when they are no longer needed.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.| Eq (StableName a) | |
makeStableName :: a -> IO (StableName a) Source
Makes a StableName for an arbitrary object. The object passed as the first argument is not evaluated by makeStableName.
hashStableName :: StableName a -> Int Source
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).
eqStableName :: StableName a -> StableName b -> Bool Source
Equality on StableName that does not require that the types of the arguments match.
Since: 4.7.0.0
© The University of Glasgow and others
Licensed under a BSD-style license (see top of the page).
https://downloads.haskell.org/~ghc/8.0.1/docs/html/libraries/base-4.9.0.0/System-Mem-StableName.html