String Concat In Loop (ARCH6070)

Key ruby.performance.string-concat-in-loop · Severity warning · Category performance

Accumulating a string with += inside a loop allocates a new string on every iteration, costing O(n^2). Use a mutable buffer or join the parts instead.

Incorrect

def build(names)
  result = ""
  names.each do |name|
    result += name + ", "
  end
  result
end

Correct

def build(names)
  names.join(", ")
end

Fix

Append in place with << instead of +=, or build the result once with join.