Why do Ruby's default parameter values not get assigned to nil arguments?
up vote
21
down vote
favorite
I'm new to Ruby and came across something that confused me a bit.
I set a default parameter value in a method signature.
When calling the method, I passed a nil argument to that parameter.
But the default value wasn't assigned; it remained nil.
# method with a default value of 1000 for parameter 'b'
def format_args(a, b=1000)
"t #{a.ljust(30,'.')} #{b}"
end
# test hash
dudes = {};
dudes["larry"] = 60
dudes["moe"] = nil
# expecting default parameter value
puts "Without nil check:"
dudes.each do |k,v|
puts format_args(k,v)
end
# forcing default parameter value
puts "With nil check:"
dudes.each do |k,v|
if v
puts format_args(k,v)
else
puts format_args(k)
end
end
Output:
Without nil check:
larry......................... 60
moe...........................
With nil check:
larry......................... 60
moe........................... 1000
Is this expected behavior?
What ruby-foo am I missing?
Seems like nil isn't the same "no value" that I'm accustomed to thinking of null in other languages.
ruby
asked May 8 '12 at 20:35
Patrick Smith
5471511
add a comment |
up vote
21
down vote
favorite
I'm new to Ruby and came across something that confused me a bit.
I set a default parameter value in a method signature.
When calling the method, I passed a nil argument to that parameter.
But the default value wasn't assigned; it remained nil.
# method with a default value of 1000 for parameter 'b'
def format_args(a, b=1000)
"t #{a.ljust(30,'.')} #{b}"
end
# test hash
dudes = {};
dudes["larry"] = 60
dudes["moe"] = nil
# expecting default parameter value
puts "Without nil check:"
dudes.each do |k,v|
puts format_args(k,v)
end
# forcing default parameter value
puts "With nil check:"
dudes.each do |k,v|
if v
puts format_args(k,v)
else
puts format_args(k)
end
end
Output:
Without nil check:
larry......................... 60
moe...........................
With nil check:
larry......................... 60
moe........................... 1000
Is this expected behavior?
What ruby-foo am I missing?
Seems like nil isn't the same "no value" that I'm accustomed to thinking of null in other languages.
ruby
asked May 8 '12 at 20:35
Patrick Smith
5471511
3
Which other language would use the default value if you give itnull?!nullis a proper value in any language I know that usesnull, just asnilis a proper value in Ruby.
– Niklas B.
May 8 '12 at 20:38
Passing a value to the function, any value, evennilfor no value, overrides the default. If you want the default, omit the argument.
– Michael Berkowski
May 8 '12 at 20:39
Yep, you're absolutely right. It's not that other languages treat it differently; it's that my mental models are screwed up and it's taking me a bit to get my head back into the code...
– Patrick Smith
May 8 '12 at 20:46
2
@MichaelBerkowski Yeah great, but if you do not have ruby 2, how would you "omit" only the second out of 3 parameters?
– user1115652
May 1 '14 at 22:16
@NiklasB. C# does it like you mention and it makes passing arguments much easier.
– Chris
Oct 23 '17 at 20:20
add a comment |
up vote
21
down vote
favorite
up vote
21
down vote
favorite
I'm new to Ruby and came across something that confused me a bit.
I set a default parameter value in a method signature.
When calling the method, I passed a nil argument to that parameter.
But the default value wasn't assigned; it remained nil.
# method with a default value of 1000 for parameter 'b'
def format_args(a, b=1000)
"t #{a.ljust(30,'.')} #{b}"
end
# test hash
dudes = {};
dudes["larry"] = 60
dudes["moe"] = nil
# expecting default parameter value
puts "Without nil check:"
dudes.each do |k,v|
puts format_args(k,v)
end
# forcing default parameter value
puts "With nil check:"
dudes.each do |k,v|
if v
puts format_args(k,v)
else
puts format_args(k)
end
end
Output:
Without nil check:
larry......................... 60
moe...........................
With nil check:
larry......................... 60
moe........................... 1000
Is this expected behavior?
What ruby-foo am I missing?
Seems like nil isn't the same "no value" that I'm accustomed to thinking of null in other languages.
ruby
asked May 8 '12 at 20:35
Patrick Smith
5471511
I'm new to Ruby and came across something that confused me a bit.
I set a default parameter value in a method signature.
When calling the method, I passed a nil argument to that parameter.
But the default value wasn't assigned; it remained nil.
# method with a default value of 1000 for parameter 'b'
def format_args(a, b=1000)
"t #{a.ljust(30,'.')} #{b}"
end
# test hash
dudes = {};
dudes["larry"] = 60
dudes["moe"] = nil
# expecting default parameter value
puts "Without nil check:"
dudes.each do |k,v|
puts format_args(k,v)
end
# forcing default parameter value
puts "With nil check:"
dudes.each do |k,v|
if v
puts format_args(k,v)
else
puts format_args(k)
end
end
Output:
Without nil check:
larry......................... 60
moe...........................
With nil check:
larry......................... 60
moe........................... 1000
Is this expected behavior?
What ruby-foo am I missing?
Seems like nil isn't the same "no value" that I'm accustomed to thinking of null in other languages.
ruby
ruby
asked May 8 '12 at 20:35
Patrick Smith
5471511
asked May 8 '12 at 20:35
Patrick Smith
5471511
edited May 8 '12 at 20:43
asked May 8 '12 at 20:35
Patrick Smith
5471511
asked May 8 '12 at 20:35
Patrick Smith
5471511
asked May 8 '12 at 20:35
Patrick Smith
5471511
5471511
3
Which other language would use the default value if you give itnull?!nullis a proper value in any language I know that usesnull, just asnilis a proper value in Ruby.
– Niklas B.
May 8 '12 at 20:38
Passing a value to the function, any value, evennilfor no value, overrides the default. If you want the default, omit the argument.
– Michael Berkowski
May 8 '12 at 20:39
Yep, you're absolutely right. It's not that other languages treat it differently; it's that my mental models are screwed up and it's taking me a bit to get my head back into the code...
– Patrick Smith
May 8 '12 at 20:46
2
@MichaelBerkowski Yeah great, but if you do not have ruby 2, how would you "omit" only the second out of 3 parameters?
– user1115652
May 1 '14 at 22:16
@NiklasB. C# does it like you mention and it makes passing arguments much easier.
– Chris
Oct 23 '17 at 20:20
add a comment |
3
Which other language would use the default value if you give itnull?!nullis a proper value in any language I know that usesnull, just asnilis a proper value in Ruby.
– Niklas B.
May 8 '12 at 20:38
Passing a value to the function, any value, evennilfor no value, overrides the default. If you want the default, omit the argument.
– Michael Berkowski
May 8 '12 at 20:39
Yep, you're absolutely right. It's not that other languages treat it differently; it's that my mental models are screwed up and it's taking me a bit to get my head back into the code...
– Patrick Smith
May 8 '12 at 20:46
2
@MichaelBerkowski Yeah great, but if you do not have ruby 2, how would you "omit" only the second out of 3 parameters?
– user1115652
May 1 '14 at 22:16
@NiklasB. C# does it like you mention and it makes passing arguments much easier.
– Chris
Oct 23 '17 at 20:20
3
3
Which other language would use the default value if you give it
null?! null is a proper value in any language I know that uses null, just as nil is a proper value in Ruby.– Niklas B.
May 8 '12 at 20:38
Which other language would use the default value if you give it
null?! null is a proper value in any language I know that uses null, just as nil is a proper value in Ruby.– Niklas B.
May 8 '12 at 20:38
Passing a value to the function, any value, even
nil for no value, overrides the default. If you want the default, omit the argument.– Michael Berkowski
May 8 '12 at 20:39
Passing a value to the function, any value, even
nil for no value, overrides the default. If you want the default, omit the argument.– Michael Berkowski
May 8 '12 at 20:39
Yep, you're absolutely right. It's not that other languages treat it differently; it's that my mental models are screwed up and it's taking me a bit to get my head back into the code...
– Patrick Smith
May 8 '12 at 20:46
Yep, you're absolutely right. It's not that other languages treat it differently; it's that my mental models are screwed up and it's taking me a bit to get my head back into the code...
– Patrick Smith
May 8 '12 at 20:46
2
2
@MichaelBerkowski Yeah great, but if you do not have ruby 2, how would you "omit" only the second out of 3 parameters?
– user1115652
May 1 '14 at 22:16
@MichaelBerkowski Yeah great, but if you do not have ruby 2, how would you "omit" only the second out of 3 parameters?
– user1115652
May 1 '14 at 22:16
@NiklasB. C# does it like you mention and it makes passing arguments much easier.
– Chris
Oct 23 '17 at 20:20
@NiklasB. C# does it like you mention and it makes passing arguments much easier.
– Chris
Oct 23 '17 at 20:20
add a comment |
4 Answers
4
active
oldest
votes
up vote
47
down vote
accepted
The default parameter is used when the parameter isn't provided.
If you provide it as nil, then it will be nil. So yes, this is expected behavior.
answered May 8 '12 at 20:39
Jeremy
19.2k45576
add a comment |
up vote
31
down vote
If you want to set a default value, even if nil is passed, and still allow calling the method without an argument you need to set the default value to nil and use the "or equals" operator:
def foo(bar=nil)
bar ||= "default value"
puts bar
end
answered Apr 28 '14 at 14:30
Mike Bethany
1,2851312
add a comment |
up vote
0
down vote
In Ruby, methods always return something. Sometimes, there is nothing to return (query in database turns up empty or something like that). nil is for those cases; It means something like 'nothing here', but it is a reference to an object. To get the behaviour you want, just pass no parameter.
def talk(msg="Hello")
puts msg
end
talk #=> "Hello"
answered May 8 '12 at 20:49
steenslag
61.6k1199137
4
Or usenilas the default argument and do amsg ||= "Hello"inside the function.
– Niklas B.
May 8 '12 at 20:52
add a comment |
up vote
0
down vote
Try ... v.is_nil? in the if statement.
answered Sep 28 '13 at 11:20
King'ori Maina
3,15921630
add a comment |
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4 Answers
4
active
oldest
votes
4 Answers
4
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
47
down vote
accepted
The default parameter is used when the parameter isn't provided.
If you provide it as nil, then it will be nil. So yes, this is expected behavior.
answered May 8 '12 at 20:39
Jeremy
19.2k45576
add a comment |
up vote
47
down vote
accepted
The default parameter is used when the parameter isn't provided.
If you provide it as nil, then it will be nil. So yes, this is expected behavior.
answered May 8 '12 at 20:39
Jeremy
19.2k45576
add a comment |
up vote
47
down vote
accepted
up vote
47
down vote
accepted
The default parameter is used when the parameter isn't provided.
If you provide it as nil, then it will be nil. So yes, this is expected behavior.
answered May 8 '12 at 20:39
Jeremy
19.2k45576
The default parameter is used when the parameter isn't provided.
If you provide it as nil, then it will be nil. So yes, this is expected behavior.
answered May 8 '12 at 20:39
Jeremy
19.2k45576
answered May 8 '12 at 20:39
Jeremy
19.2k45576
answered May 8 '12 at 20:39
Jeremy
19.2k45576
answered May 8 '12 at 20:39
Jeremy
19.2k45576
19.2k45576
add a comment |
add a comment |
up vote
31
down vote
If you want to set a default value, even if nil is passed, and still allow calling the method without an argument you need to set the default value to nil and use the "or equals" operator:
def foo(bar=nil)
bar ||= "default value"
puts bar
end
answered Apr 28 '14 at 14:30
Mike Bethany
1,2851312
add a comment |
up vote
31
down vote
If you want to set a default value, even if nil is passed, and still allow calling the method without an argument you need to set the default value to nil and use the "or equals" operator:
def foo(bar=nil)
bar ||= "default value"
puts bar
end
answered Apr 28 '14 at 14:30
Mike Bethany
1,2851312
add a comment |
up vote
31
down vote
up vote
31
down vote
If you want to set a default value, even if nil is passed, and still allow calling the method without an argument you need to set the default value to nil and use the "or equals" operator:
def foo(bar=nil)
bar ||= "default value"
puts bar
end
answered Apr 28 '14 at 14:30
Mike Bethany
1,2851312
If you want to set a default value, even if nil is passed, and still allow calling the method without an argument you need to set the default value to nil and use the "or equals" operator:
def foo(bar=nil)
bar ||= "default value"
puts bar
end
answered Apr 28 '14 at 14:30
Mike Bethany
1,2851312
answered Apr 28 '14 at 14:30
Mike Bethany
1,2851312
answered Apr 28 '14 at 14:30
Mike Bethany
1,2851312
answered Apr 28 '14 at 14:30
Mike Bethany
1,2851312
1,2851312
add a comment |
add a comment |
up vote
0
down vote
In Ruby, methods always return something. Sometimes, there is nothing to return (query in database turns up empty or something like that). nil is for those cases; It means something like 'nothing here', but it is a reference to an object. To get the behaviour you want, just pass no parameter.
def talk(msg="Hello")
puts msg
end
talk #=> "Hello"
answered May 8 '12 at 20:49
steenslag
61.6k1199137
4
Or usenilas the default argument and do amsg ||= "Hello"inside the function.
– Niklas B.
May 8 '12 at 20:52
add a comment |
up vote
0
down vote
In Ruby, methods always return something. Sometimes, there is nothing to return (query in database turns up empty or something like that). nil is for those cases; It means something like 'nothing here', but it is a reference to an object. To get the behaviour you want, just pass no parameter.
def talk(msg="Hello")
puts msg
end
talk #=> "Hello"
answered May 8 '12 at 20:49
steenslag
61.6k1199137
4
Or usenilas the default argument and do amsg ||= "Hello"inside the function.
– Niklas B.
May 8 '12 at 20:52
add a comment |
up vote
0
down vote
up vote
0
down vote
In Ruby, methods always return something. Sometimes, there is nothing to return (query in database turns up empty or something like that). nil is for those cases; It means something like 'nothing here', but it is a reference to an object. To get the behaviour you want, just pass no parameter.
def talk(msg="Hello")
puts msg
end
talk #=> "Hello"
answered May 8 '12 at 20:49
steenslag
61.6k1199137
In Ruby, methods always return something. Sometimes, there is nothing to return (query in database turns up empty or something like that). nil is for those cases; It means something like 'nothing here', but it is a reference to an object. To get the behaviour you want, just pass no parameter.
def talk(msg="Hello")
puts msg
end
talk #=> "Hello"
answered May 8 '12 at 20:49
steenslag
61.6k1199137
answered May 8 '12 at 20:49
steenslag
61.6k1199137
answered May 8 '12 at 20:49
steenslag
61.6k1199137
answered May 8 '12 at 20:49
steenslag
61.6k1199137
61.6k1199137
4
Or usenilas the default argument and do amsg ||= "Hello"inside the function.
– Niklas B.
May 8 '12 at 20:52
add a comment |
4
Or usenilas the default argument and do amsg ||= "Hello"inside the function.
– Niklas B.
May 8 '12 at 20:52
4
4
Or use
nil as the default argument and do a msg ||= "Hello" inside the function.– Niklas B.
May 8 '12 at 20:52
Or use
nil as the default argument and do a msg ||= "Hello" inside the function.– Niklas B.
May 8 '12 at 20:52
add a comment |
up vote
0
down vote
Try ... v.is_nil? in the if statement.
answered Sep 28 '13 at 11:20
King'ori Maina
3,15921630
add a comment |
up vote
0
down vote
Try ... v.is_nil? in the if statement.
answered Sep 28 '13 at 11:20
King'ori Maina
3,15921630
add a comment |
up vote
0
down vote
up vote
0
down vote
Try ... v.is_nil? in the if statement.
answered Sep 28 '13 at 11:20
King'ori Maina
3,15921630
Try ... v.is_nil? in the if statement.
answered Sep 28 '13 at 11:20
King'ori Maina
3,15921630
answered Sep 28 '13 at 11:20
King'ori Maina
3,15921630
answered Sep 28 '13 at 11:20
King'ori Maina
3,15921630
answered Sep 28 '13 at 11:20
King'ori Maina
3,15921630
3,15921630
add a comment |
add a comment |
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3
Which other language would use the default value if you give it
null?!nullis a proper value in any language I know that usesnull, just asnilis a proper value in Ruby.– Niklas B.
May 8 '12 at 20:38
Passing a value to the function, any value, even
nilfor no value, overrides the default. If you want the default, omit the argument.– Michael Berkowski
May 8 '12 at 20:39
Yep, you're absolutely right. It's not that other languages treat it differently; it's that my mental models are screwed up and it's taking me a bit to get my head back into the code...
– Patrick Smith
May 8 '12 at 20:46
2
@MichaelBerkowski Yeah great, but if you do not have ruby 2, how would you "omit" only the second out of 3 parameters?
– user1115652
May 1 '14 at 22:16
@NiklasB. C# does it like you mention and it makes passing arguments much easier.
– Chris
Oct 23 '17 at 20:20