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Blocks not Parameters for logging debug information in Ruby

Okay, it really matters if you've got to log your debug information that is more than a plain dumb string without any concatenation.

Let's take our typical habit of writing a debug like below:
logger.debug("This is a " + potentially + " expensive operation")

The above snippet could be better written as below:
logger.debug { "This is a " + potentially + " expensive operation" }

The block form is recommended because the code in the block is evaluated only if the debug log is to be written/logged. 

[Ruby Doc] How to log a message?

Book Recommendation:
[Book] Ruby Programming: The well-grounded Rubyist