Hi James, 2010/8/11 James Ladd <james_l...@hotmail.com>
> Hi Eliot, > > That is a very nice blog you linked me to. Lots for me to read there. > > I read this ... > > The final bytecode is more interesting. > 143 10001111 llllkkkk jjjjjjjj iiiiiiii Push > Closure Num Copied llll Num Args kkkk BlockSize jjjjjjjjiiiiiiii > This creates a closure, initializing it from the arguments and the current > context. > > I'm missing something, is "num copied llll" the number of temps copied > from the containing method? > It is the number of values copied from the stack that become locals of the closure. In Collection>>inject: thisValue into: binaryBlock "Accumulate a running value associated with evaluating the argument, binaryBlock, with the current value of the argument, thisValue, and the receiver as block arguments. For instance, to sum the numeric elements of a collection, aCollection inject: 0 into: [:subTotal :next | subTotal + next]." | nextValue | nextValue := thisValue. self do: [:each | nextValue := binaryBlock value: nextValue value: each]. ^nextValue the closure [:each | nextValue := binaryBlock value: nextValue value: each] accesses two non-local variables binaryBlock & nextValue. Because binaryBlock is not modified its value can be copied directly but because nextValue is modified it cannot be copied and a shared location must be used to hold the value. So the compiler arranges to create an (in this case one-element) array (an indirection vector) to hold nextValue. The hidden variable holding the indirection vector is not modified so its value (the indirection vector) can be copied. Hence [:each | nextValue := binaryBlock value: nextValue value: each] has two copied values, one the value of binaryBlock and another a hidden Array that holds nextValue. Hence the bytecode: push: (Array new: 1) # create the indirection vector popIntoTemp: 2 # store it as the 3rd temp (after firstValue & binaryBlock) pushTemp: 0 # push firstValue popIntoTemp: 0 inVectorAt: 2 # initialize nextValue with firstValue self # push the receiver of #do: pushTemp: 1 # push the first copied value binaryBlock pushTemp: 2 # push the second copied value, the indirection vector holding nextValue closureNumCopied: 2 numArgs: 1 bytes 31 to 40 # create the closure with 1 arg and 2 copied values pushTemp: 1 # push binaryBlock (the 1st copied value, the 2nd temp after each) pushTemp: 0 inVectorAt: 2 # push nextValue, the 1st slot in the indirection vector which is the 3rd temp pushTemp: 0 # push each send: #value:value: (2 args) # evaluate binaryBlock value: nextValue value: each storeIntoTemp: 0 inVectorAt: 2 # store the result into nextValue (1st slot in indirection vector) blockReturn # return nextValue as the result of the block send: #do: (1 arg) # evaluate self do: [:each|...] pop # discard the result of elf do: [:each|...] pushTemp: 0 inVectorAt: 2 # push nextValue returnTop # return nextValue as the result of inject:into: If this still doesn't make sense look at the version in the first blog post that uses an explicit array and compare it with the above. HTH Eliot > Rgs, James. > > _______________________________________________ > Pharo-project mailing list > Pharo-project@lists.gforge.inria.fr > http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project >
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