confirm that using &block does an extra allocation making it almost 7X slower than using yield.

yield_vs_call

$ ruby --version
ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-darwin11.0.0]

$ time ruby -e "def foo(&block); block.call; end; 2_000_000.times{ foo{1+1} };"

real	0m1.556s
user	0m1.482s
sys	0m0.075s

$ time ruby -e "def foo; yield; end; 2_000_000.times{ foo{1+1} };"

real	0m0.233s
user	0m0.229s
sys	0m0.003s

$ time ruby -e "def foo(&block); block.call if block; end; 2_000_000.times{ foo{1+1} };"

real	0m1.609s
user	0m1.533s
sys	0m0.077s

$ time ruby -e "def foo; yield if block_given?; end; 2_000_000.times{ foo{1+1} };"

real	0m0.342s
user	0m0.338s
sys	0m0.003s

Yup, it's slower. Too slow or significant enough? That's a matter of context.