ruby-blocks-procs-lambdas（Ruby blocks procs lambdas 命令行）

Ruby Blocks, Procs, and Lambdas

Master Ruby's functional programming features with blocks, procs, and lambdas. These are fundamental to Ruby's expressive and elegant style.

Blocks

Basic Block Syntax

# Block with do...end (multi-line)
[1, 2, 3].each do |num|
  puts num * 2
end

# Block with {...} (single line)
[1, 2, 3].each { |num| puts num * 2 }

Yielding to Blocks

def repeat(times)
  times.times do
    yield  # Execute the block
  end
end

repeat(3) { puts "Hello" }

# With block parameters
def greet
  yield("World")
end

greet { |name| puts "Hello, #{name}!" }

Block Arguments

def process_data(data)
  result = yield(data)
  puts "Result: #{result}"
end

process_data(10) { |x| x * 2 }  # Result: 20

Checking for Blocks

def optional_block
  if block_given?
    yield
  else
    puts "No block provided"
  end
end

optional_block { puts "Block executed" }
optional_block

Block Local Variables

x = 10

[1, 2, 3].each do |num; local_var|
  local_var = num * 2  # local_var only exists in block
  puts local_var
end

puts x  # 10 (unchanged)

Procs

Creating Procs

# Using Proc.new
my_proc = Proc.new { |x| x * 2 }
puts my_proc.call(5)  # 10

# Using proc method (deprecated in some versions)
my_proc = proc { |x| x * 2 }

# Using -> (stabby lambda syntax for Proc)
my_proc = ->(x) { x * 2 }

Proc Characteristics

# Procs don't care about argument count
flexible_proc = Proc.new { |x, y| "x: #{x}, y: #{y}" }
puts flexible_proc.call(1)     # x: 1, y:
puts flexible_proc.call(1, 2, 3)  # x: 1, y: 2 (ignores extra)

# Procs return from the enclosing method
def proc_return
  my_proc = Proc.new { return "from proc" }
  my_proc.call
  "after proc"  # Never reached
end

puts proc_return  # "from proc"

Passing Procs as Arguments

def execute_proc(my_proc)
  my_proc.call
end

greeting = Proc.new { puts "Hello from proc!" }
execute_proc(greeting)

Converting Blocks to Procs

def method_with_proc(&block)
  block.call
end

method_with_proc { puts "Block converted to proc" }

Lambdas

Creating Lambdas

# Using lambda keyword
my_lambda = lambda { |x| x * 2 }

# Using -> (stabby lambda)
my_lambda = ->(x) { x * 2 }

# Multi-line stabby lambda
my_lambda = ->(x) do
  result = x * 2
  result + 1
end

puts my_lambda.call(5)  # 11

Lambda Characteristics

# Lambdas enforce argument count
strict_lambda = ->(x, y) { x + y }
# strict_lambda.call(1)     # ArgumentError
strict_lambda.call(1, 2)    # Works

# Lambdas return to the caller
def lambda_return
  my_lambda = -> { return "from lambda" }
  my_lambda.call
  "after lambda"  # This IS reached
end

puts lambda_return  # "after lambda"

Lambda with Multiple Arguments

add = ->(x, y) { x + y }
multiply = ->(x, y, z) { x * y * z }

puts add.call(3, 4)         # 7
puts multiply.call(2, 3, 4) # 24

# Default arguments
greet = ->(name = "World") { "Hello, #{name}!" }
puts greet.call           # "Hello, World!"
puts greet.call("Ruby")   # "Hello, Ruby!"

Proc vs Lambda

# Argument handling
my_proc = Proc.new { |x, y| puts "x: #{x}, y: #{y}" }
my_lambda = ->(x, y) { puts "x: #{x}, y: #{y}" }

my_proc.call(1)     # Works: x: 1, y:
# my_lambda.call(1) # ArgumentError

# Return behavior
def test_return
  proc_test = Proc.new { return "proc return" }
  lambda_test = -> { return "lambda return" }

  proc_test.call   # Returns from method
  "end"            # Never reached
end

def test_lambda
  lambda_test = -> { return "lambda return" }
  lambda_test.call # Returns from lambda
  "end"            # This IS reached
end

# Check if it's a lambda
my_proc = Proc.new { }
my_lambda = -> { }

puts my_proc.lambda?   # false
puts my_lambda.lambda? # true

Closures

def multiplier(factor)
  ->(x) { x * factor }
end

times_two = multiplier(2)
times_three = multiplier(3)

puts times_two.call(5)    # 10
puts times_three.call(5)  # 15

# Closures capture variables
def counter
  count = 0

  increment = -> { count += 1 }
  decrement = -> { count -= 1 }
  value = -> { count }

  [increment, decrement, value]
end

inc, dec, val = counter
inc.call
inc.call
puts val.call  # 2
dec.call
puts val.call  # 1

Method Objects

class Calculator
  def add(x, y)
    x + y
  end
end

calc = Calculator.new
add_method = calc.method(:add)
puts add_method.call(3, 4)  # 7

# Converting methods to procs
add_proc = calc.method(:add).to_proc
puts add_proc.call(5, 6)  # 11

Symbol to Proc

# & converts symbol to proc
numbers = [1, 2, 3, 4, 5]

# These are equivalent:
numbers.map { |n| n.to_s }
numbers.map(&:to_s)

# Works with any method
["hello", "world"].map(&:upcase)  # ["HELLO", "WORLD"]
[1, 2, 3].select(&:even?)         # [2]

Higher-Order Functions

def compose(f, g)
  ->(x) { f.call(g.call(x)) }
end

double = ->(x) { x * 2 }
square = ->(x) { x * x }

double_then_square = compose(square, double)
puts double_then_square.call(3)  # 36 (3 * 2 = 6, 6 * 6 = 36)

Currying

# Manual currying
add = ->(x) { ->(y) { x + y } }
add_five = add.call(5)
puts add_five.call(3)  # 8

# Built-in currying
multiply = ->(x, y, z) { x * y * z }
curried = multiply.curry
times_two = curried.call(2)
times_two_three = times_two.call(3)
puts times_two_three.call(4)  # 24

# Partial application
puts curried.call(2, 3).call(4)  # 24

Practical Patterns

Lazy Evaluation

def lazy_value
  puts "Computing expensive value..."
  42
end

# Wrap in lambda for lazy evaluation
lazy = -> { lazy_value }

puts "Before call"
result = lazy.call  # Only computed here
puts result

Callback Pattern

class Button
  def initialize
    @on_click = []
  end

  def on_click(&block)
    @on_click << block
  end

  def click
    @on_click.each(&:call)
  end
end

button = Button.new
button.on_click { puts "Button clicked!" }
button.on_click { puts "Another handler" }
button.click

Strategy Pattern

class Sorter
  def initialize(strategy)
    @strategy = strategy
  end

  def sort(array)
    @strategy.call(array)
  end
end

ascending = ->(arr) { arr.sort }
descending = ->(arr) { arr.sort.reverse }

sorter = Sorter.new(ascending)
puts sorter.sort([3, 1, 2])  # [1, 2, 3]

sorter = Sorter.new(descending)
puts sorter.sort([3, 1, 2])  # [3, 2, 1]

Memoization

def memoize(&block)
  cache = {}
  ->(arg) do
    cache[arg] ||= block.call(arg)
  end
end

expensive_operation = memoize do |n|
  puts "Computing for #{n}..."
  n * n
end

puts expensive_operation.call(5)  # Computing for 5... 25
puts expensive_operation.call(5)  # 25 (cached)

Best Practices

1. Use blocks for simple iteration and single-use closures
2. Use lambdas for strict argument checking and returnable closures
3. Use procs for flexible argument handling (rare cases)
4. Prefer -> syntax for lambdas (more concise)
5. Use &:symbol for simple method calls on collections
6. Leverage closures for encapsulation and data privacy
7. Use block_given? before yielding to optional blocks

Anti-Patterns

❌ Don't use Proc.new for strict behavior - use lambda instead ❌ Don't ignore return behavior - understand proc vs lambda differences ❌ Don't overuse closures - can lead to memory leaks if not careful ❌ Don't create deeply nested lambdas - hard to read and debug ❌ Don't forget to handle missing blocks - check with block_given?

Related Skills

• ruby-oop - For understanding method context
• ruby-metaprogramming - For dynamic block/proc usage
• ruby-standard-library - For Enumerable methods using blocks