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Re: Recursive blocks
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Re: Recursive blocks


  • Subject: Re: Recursive blocks
  • From: Chris Suter <email@hidden>
  • Date: Fri, 28 Jan 2011 10:38:53 +1100

Hi Bill,

On Fri, Jan 28, 2011 at 4:51 AM, Bill Bumgarner <email@hidden> wrote:

> You have measured a situation where the pattern's marginal slowness actually
> matters?

No, of course not; I don't have a real world use case for it and, I
suspect, neither does anyone else.

> A Block_copy() is going to often be at least an order of magnitude (if not
> more) slower because it ends up causing a malloc().   Given that there will
> only be one allocation (or one assignment), it is likely that the overhead
> of either will be in the noise.

I was actually hinting at the slowness caused by using a block
variable. I forget exactly how many levels of indirection the block
variable incurs, three perhaps vs. a single call instruction, and
there's no way for the compiler to optimise it.

As you say, it's unlikely to make a difference but if you were to use
tail recursion and have a large number of iterations, then it might.

> I found the Blocks example to be more readable, but to each his own.

When I say readable, I also mean less prone to error. If you forget
the __block type qualifier, you don't get a compiler warning. Also if
you were stupid enough to reuse the block variable later that would
change the behaviour of the earlier block.

It also smells. Using a block variable to call yourself recursively is a hack.

Kind regards,

Chris
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