This short cut focuses on a number of coding patterns that are useful when trying to get maximum speed out of performance-critical sections of Ruby code. Anti-patterns, that is, coding idioms, which should be avoided in performance-sensitive code sections are discussed, including details on how to transform such code to make it more efficient. Most patterns were extracted from Stefan Kaes' work on improving performance of the Rails core and his regular Rails performance consulting work. These patterns are largely non-algorithmic, detailing local code transformations to achieve identical results with slightly different and faster code, as even local code changes can sometimes result in orders of magnitude improvements. Some patterns are useful independent of Rails' implementation language, but some of them are specific to Ruby, or more specifically, the current implementation of Ruby. Converts from other languages, especially from statically typed languages such as Java or C++ may find this material useful, as the performance characteristics of certain operations, like performing a function call or accessing object fields/attributes, are quite different from what you expect.
What This Short Cut Covers
Ruby's Interpreter Is Slow
Runtime Complexity of Ruby Language Constructs
Instance Variables versus Accessors Local Variables Are Cheap Assignments in Expressions Interpolated Strings In-Place Updates Sets versus Arrays For Loops versus each Make Decisions at Load Time Self Modifying Code Test Most Frequent Case First Optimize Access to Global Constants Caching Data in Instance Variables Caching Data in Class Variables Coding Variable Caching Efficiently Initializing Variables with nil Using .nil? nil? or empty? versus blank? Using return Using returning Using any? Block Local Variables Date Formatting Temporary Datastructure Constants File System Access ObjectSpace.each_object Unnecessary Block Parameters Symbol.to_proc Chained Calls of map Requiring Files Dynamically Including Modules versus Opening Classes
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