bsdshell

## unpack_ghc.md

      
        
          
            
              
              1 file
            
          
          
            
              
              0 forks
            
          
          
            
              
              0 comments
            
          
          
            
              
              1 star
            
          
        
        
          
              
          
          
            
                monadplus
                / unpack_ghc.md
            
            
              Last active
              February 28, 2023 23:34
            
              
                Unpacking strict fields (Source: https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/glasgow_exts.html#unpack-pragma)
              
          
        
      
        
  
      
    {-# UNPACK #-} Unpacking strict fields

This is one of the most powerful techniques you can use to optimise data structures.
When a constructor field is marked strict, and it is a single-constructor type,
then it is possible to ask GHC to unpack the contents of the field directly in its parent.
For example, given this:
data T = T {-# UNPACK #-} !(Int,Float)