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Ruby Method: Def, Arguments and Return Values
Review the syntax of methods: receive parameters and return values with methods.Here: We see a nested method call in the final assignment. We call the calculate() method with an argument of 2.
Return: This returns 200. We then pass that value, 200, to the calculate method again, which again multiplies by 100.
Ruby program that calls method
def calculate(value)
# Multiply by 100 and return.
return value * 100
end
# Call calculate method.
result1 = calculate(5)
result2 = calculate(10)
result3 = calculate(calculate(2))
# Print results.
print result1, "\n"
print result2, "\n"
print result3, "\n"
Output
500
1000
20000
So: When we call compute with two explicit parameters (5, 5) neither of the defaults are used.
However: When we use just one parameter, the second argument (height) uses the default value of 10.
Finally: We invoke the compute method with no arguments. The defaults are both used. So we get a result of 10 times 10, or 100.
Ruby program that uses default parameters
def compute(width = 10, height = 10)
# Uses default values for parameters if not specified.
return width * height
end
# 5 times 5.
puts compute(5, 5)
# 5 times 10.
puts compute(5)
# 10 times 10.
puts compute
Output
25
50
100
Here: We specify no return keyword in the test method. We call it with two arguments (and omit the parentheses).
Important: This syntax form does not work if we have multiple return statements in a method. The "return" is required.
Ruby program that uses implicit return value
def test(x, y)
# This expression is evaluated and returned.
(x * 10) + y
end
# Call test with two arguments.
result = test 5, 10
# Display the result.
# ... (5 * 10) + 10 = 60
puts result
Output
60
Tip: To specify a keyword argument (in the def itself or the method call) please use a ":" after an identifier in the argument list.
Tip 2: Positional arguments (those specified by position, not keyword) must come before keyword arguments.
Ruby program that uses keyword arguments
def display(name: "?", id: 0, size: 0)
# Display all keyword arguments.
print "Name: ", name, "\n"
print "Id: ", id, "\n"
print "Size: ", size, "\n"
end
# Call method with keyword arguments.
display(id: 10, size: 5, name: "cat")
Output
Name: cat
Id: 10
Size: 5
Note: This syntax is similar to calling a method with an explicit array. The syntax may be clearer in some contexts.
However: In my experience, using explicit arrays is often better. It makes the usage of the def methods more obvious.
Ruby program that uses variable arguments
def test(*items)
# Iterate over the elements in the array.
items.each do |item|
puts item
end
end
# Call with three arguments.
test("abc", "def", "ghi")
Output
abc
def
ghi
Ruby program that uses alias on method
def method()
puts "Hello"
end
# Alias the identifier "m" to "method"
alias m method
# Call method.
m()
Output
Hello
Note: The positions of BEGIN and END in the source file do not matter. END may be used like an "ensure" statement for an entire file.
Ruby program that uses BEGIN, END
# Code in BEGIN is run before anything else.
BEGIN {
puts(1)
}
# Code in END is run afterwards.
END {
puts(2)
}
# This is after BEGIN and before END.
puts "Middle"
Output
1
Middle
2
Note: The question mark means the method is a predicate—it returns true or false.
Undef: With undef we can erase a method and make it no longer accessible. We modify the program during execution.
Ruby program that uses defined, undef
def test()
puts "Hello world"
end
# The test method is now defined.
if defined?(test)
puts true
end
# Undefine the method.
undef test
# The method is no longer defined.
if !defined?(test)
puts false
end
Output
true
false
Ruby program that uses empty method, nil
# This empty method returns nil.
def test
end
# Test return value of method.
if test() == nil
puts true
end
Output
true
Tip: When designing recursive algorithms, the memory model of your language is important. Some objects may need to be copied.
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