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TypeCache documentation

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This commit is contained in:
Greg Weber 2014-09-24 09:04:41 -07:00
parent 510f70d5b3
commit 8fd0378c4b
1 changed files with 10 additions and 9 deletions
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19
yesod-core/Yesod/Core/TypeCache.hs
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@ -1,12 +1,13 @@
-- | a module for caching a monadic action based on its return type -- | a module for caching a monadic action based on its return type
-- --
-- The cache is a HashMap where the key uses the result of typeOf from Typeable. -- The cache is a HashMap where the key uses the TypeReP from Typeable.
-- The value stored is toDyn from Dynamic to support arbitrary value types. -- The value stored is toDyn from Dynamic to support arbitrary value types in the same Map.
-- --
-- un-exported newtype wrappers should be used to maintain unique keys in the cache. -- un-exported newtype wrappers should be used to maintain unique keys in the cache.
-- Note that a TypeRep is unique to a module in a package, so types from different modules will not conflict if they have the same name.
-- --
-- used in 'Yesod.Core.Handler.cached' and 'Yesod.Core.Handler.cachedBy' -- used in 'Yesod.Core.Handler.cached' and 'Yesod.Core.Handler.cachedBy'
module Yesod.Core.TypeCache where module Yesod.Core.TypeCache (cached, cachedBy) where
import Prelude hiding (lookup) import Prelude hiding (lookup)
import Data.Typeable (Typeable, TypeRep, typeOf) import Data.Typeable (Typeable, TypeRep, typeOf)
@ -18,16 +19,16 @@ type TypeMap = HashMap TypeRep Dynamic
type KeyedTypeMap = HashMap (TypeRep, ByteString) Dynamic type KeyedTypeMap = HashMap (TypeRep, ByteString) Dynamic
-- | avoid performing the same action multiple times. -- | avoid performing the same action multiple times.
-- Values are stored by their type, the result of typeOf from Typeable. -- Values are stored by their TypeRep from Typeable.
-- Therefore, you should use different newtype wrappers at each cache site. -- Therefore, you should use un-exported newtype wrappers for each cache.
-- --
-- For example, yesod-auth uses an un-exported newtype, CachedMaybeAuth and exports functions that utilize it such as maybeAuth. -- For example, yesod-auth uses an un-exported newtype, CachedMaybeAuth and exports functions that utilize it such as maybeAuth.
-- This means that another module can create its own newtype wrapper to cache the same type from a different action without any cache conflicts. -- This means that another module can create its own newtype wrapper to cache the same type from a different action without any cache conflicts.
-- --
-- In Yesod, this is used for a cache that is cleared at the end of every request. -- In Yesod, this is used for a request-local cache that is cleared at the end of every request.
-- See the original announcement: <http://www.yesodweb.com/blog/2013/03/yesod-1-2-cleaner-internals> -- See the original announcement: <http://www.yesodweb.com/blog/2013/03/yesod-1-2-cleaner-internals>
-- --
-- Since 1.2.0 -- Since 1.4.0
cached :: (Monad m, Typeable a) cached :: (Monad m, Typeable a)
=> TypeMap => TypeMap
-> m a -> m a
@ -49,9 +50,9 @@ cached cache action = case clookup cache of
cinsert :: Typeable a => a -> TypeMap -> TypeMap cinsert :: Typeable a => a -> TypeMap -> TypeMap
cinsert v = insert (typeOf v) (toDyn v) cinsert v = insert (typeOf v) (toDyn v)
-- | like 'cached'. -- | similar to 'cached'.
-- 'cached' can only cache a single value per type. -- 'cached' can only cache a single value per type.
-- 'cachedBy' stores multiple values per type by usage of a ByteString key -- 'cachedBy' stores multiple values per type by indexing on a ByteString key
-- --
-- 'cached' is ideal to cache an action that has only one value of a type, such as the session's current user -- 'cached' is ideal to cache an action that has only one value of a type, such as the session's current user
-- 'cachedBy' is required if the action has parameters and can return multiple values per type. -- 'cachedBy' is required if the action has parameters and can return multiple values per type.