Optimize SqlString.format

[ghost]

I was looking for ways to speed up mysql.format after noticing that the performance was very slow when attempting to format a query with 100,000+ values. I came up with a couple of improvements, by far the most significant is to use an iterator to step through the values array instead of Array.shift(). See: http://jsperf.com/some-array-reading-comparisons/6

[ghost]

See also:

http://stackoverflow.com/questions/27341352/why-does-a-a-nodejs-array-shift-push-loop-run-1000x-slower-above-array-length-87

[ghost]

May fix #937

[dougwilson]

This sounds good to me, but please make sure that the values array stays altered in the same way in the end as it used to be; there are unfortunately people relying on the fact that the array they are passing in gets emptied (or only emptied up to the number of ? in the SQL).

[dougwilson]

Or nevermind my statement above; :) I'll doube-check that for realz and most likely I'll merge your code :O

[ghost]

Hold off on that merge. With this change my test suite for my application is failing. Could be an obscure use case. I will update here after I sort it out.

Never mind sentence above. It had nothing to do with this change, I was mistaken.

[ronkorving]

No need for array copying, as you're not modifying it anymore. More win :)

[dougwilson]

@ronkorving feel free to make a PR :) And remember that the values argument may not always be an array.

[ronkorving]

Ouch, I missed that it can be an object too. Then there's nothing to gain here. My bad.