add toStrictByteString

Changelog.md

@@ -5,6 +5,7 @@
 * [Remove `zipWith` rewrite rule](https://github.com/haskell/bytestring/pull/387)
 * [`ShortByteString` is now a wrapper over boxed `Data.Array.Byte.ByteArray` instead of unboxed `ByteArray#` directly](https://github.com/haskell/bytestring/pull/410)
 * [`fromListN` from `instance IsList ShortByteString` throws an exception if the first argument does not match the length of the second instead of silent ignore](https://github.com/haskell/bytestring/pull/410)
+* [Add `toStrictByteString` to `Data.ByteString.Builder`](https://github.com/haskell/bytestring/pull/589)
 
 [0.12.0.0]: https://github.com/haskell/bytestring/compare/0.11.4.0...0.12.0.0
 

Data/ByteString/Builder.hs

@@ -189,6 +189,7 @@ module Data.ByteString.Builder
       -- cases. See "Data.ByteString.Builder.Extra", for information
       -- about fine-tuning them.
     , toLazyByteString
+    , toStrictByteString
     , hPutBuilder
     , writeFile
 
@@ -260,6 +261,7 @@ import           Prelude hiding (writeFile)
 
 import           Data.ByteString.Builder.Internal
 import qualified Data.ByteString.Builder.Prim  as P
+import qualified Data.ByteString.Internal as S
 import qualified Data.ByteString.Lazy.Internal as L
 import           Data.ByteString.Builder.ASCII
 import           Data.ByteString.Builder.RealFloat
@@ -278,6 +280,14 @@ toLazyByteString :: Builder -> L.ByteString
 toLazyByteString = toLazyByteStringWith
     (safeStrategy L.smallChunkSize L.defaultChunkSize) L.Empty
 
+-- | Execute a 'Builder' and pack the resulting chunks into a strict 'S.ByteString'.
+--
+-- @'toStrictByteString' = 'L.toStrict' . 'toLazyByteString'@
+--
+{-# INLINABLE toStrictByteString #-}
+toStrictByteString :: Builder -> S.ByteString
+toStrictByteString = L.toStrict . toLazyByteString
+
 {- Not yet stable enough.
    See note on 'hPut' in Data.ByteString.Builder.Internal
 -}