CODEWITHSUNDEEP
rubylambda
mbdev
mbdev

Reputation: 6573

Determine if a parameter/variable is a ("is_a?") lambda?

How to check if a given parameter is a lambda?

def method(parameter)
  if ???
      puts "We got lambda"
      parameter.call
  else
      puts "I did not get a block"
  end
end


method(lambda { 1 })
method(1)

Upvotes: 27

Views: 12231

Answers (2)

CamiloVA
CamiloVA

Reputation: 731

Actually you can check if variable is_a? a Proc

x = (lambda {})
x.is_a?(Proc) # true

Upvotes: 4

user166390
user166390

Reputation:

A block is not a lambda. To see if there is a block use block_given?.

In any case, I would use "responds to call" if and only if I really needed this construct, which I would try to avoid. (Define the contract and make the caller responsible for invoking it correctly!)

 (lambda {1}).respond_to? :call # => true
 (1).respond_to? :call          # => false

I believe this form of structural (aka duck) typing is more inline with Ruby than nominative typing with "is a" relationships.

To see what "is a" relationships might hold (for future playing in a sandbox):

 RUBY_VERSION           # => 1.9.2
 (lambda {}).class      # => Proc
 (Proc.new {}).class    # => Proc
 def x (&p); p; end     # note this "lifts" the block to a Proc
 (x {}).class           # => Proc

Happy coding.

Upvotes: 45

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