What is the difference between a block, a proc and a lambda?
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01
Core Competency
Assesses fundamental understanding of Ruby conventions, runtime behavior, and memory/performance considerations.
02
Evaluation Criteria
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
Comprehensive Model Answer
Verified Solution
All three are chunks of code, but they differ in argument checking and how return behaves.
- A
blockis passed to a method withdo...endor braces and is not a standalone object unless converted with&. - A
procdoes not check argument count: missing arguments become nil and extras are dropped. Areturnreturns from the enclosing method and can raiseLocalJumpErrorif that method already returned. - A
lambdachecks arity strictly, andreturnreturns only from the lambda.
def run(callable)
callable.call
:after
end
l = -> { return :from_lambda }
puts run(l) # :after
pr = proc { return :from_proc }
# run(pr) raises LocalJumpError
Lambdas are usually preferred because they behave like methods. Check with lambda?. Blocks are typically yielded once and converted to a Proc through the &block parameter.
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