Eliminating Intermediate Array Allocations
Recently I gave a talk at RailsWorld (hopefully they’ll post the video soon), and part of my presentation was about eliminating allocations in tokenizers. I presented a simple function for measuring allocations:
Everything in Ruby is an object, but not all objects actually make allocations. We can use the above function to measure allocations made in a block. Here are some examples of code that never allocate:
Literals like booleans, nil, symbols, integers, and floats are represented internally to CRuby as “tagged pointers” and they don’t allocate anything when executed.
Math on integers generally doesn’t allocate anything, but it depends on the integer. When a number gets large enough, CRuby will allocate an object to represent that number. On 64 bit platforms, the largest whole number we can represent without allocating is 0x3FFF_FFFF_FFFF_FFFF.
At the Shopify after-party at RailsWorld, someone asked me a really great question. Their codebase has a RuboCop rule that says that when doing min or max calculations, you should always have code like this:
