Comment by dbaupp | Hacker News Reader

Comment by dbaupp | Hacker News Reader

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Regarding your last question: the string concatenation/evaluation happens once while creating the parseRow function and from then parseRow is a compiled/JIT'd function object, no string handling happening. The problem with the original is not the hash map creation, but the fact that it requires all sorts of extra loops, and array & property look-ups.

Also, I think that is possibly some missing information there, since in the second version the column names are fixed (so the columns argument to parseRow is ignored), while in the first they are not.

Ah ok so this is probably the parser equivalent to precompiled queries. Given a fixed query, a specific parse row function is created once and than reused. Thanks!

While I think code generation is certainly the right approach in some examples, I see one problem in this example: As the parser is basically pregenerated using a certain column definition, why does the generated function has an parameter columns? It is simply discarded. So I would say it should rather be:

  var parseRow = new Function('parser', code);

I agree, and I don't know. (I even looked through the source to try to find if parseRow is a function from node-mysql. It's not, as far as I could tell.)

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