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Conceptually, nil != false. You shouldn't use 'nil' to mean 'false'. You should always test explicitly for nil-ness using #nil?. If you write if finished?

Conceptually, nil != false. You shouldn't use 'nil' to mean 'false'. You should always test explicitly for nil-ness using #nil?. If you write if finished? do_something end then finished? is not expected, and may not, return nil. If you expect some_value to be able to be nil (which, for boolean values, is hardly ever), you should write if !some_value.nil? && some_value do_something end In the end, these 'convenient' coercions that allow you to use any value as a boolean only come back to bite you, because unexpected stuff happens when stuff is unexpectedly nil. If it makes my coworkers cry that an object is nil and true at the same time, then they are at fault, not me. Edit: and more importantly (I forgot to point this out explicitly) a non-nil value != true. That any string or integer is 'true' can lead to very hard-to-find bugs.

necubi 15y ago
Such code is everywhere in the Ruby community and explicitly endorsed by many. I have never seen code like your second example in the wild, and it's far more complicated than the idiomatic way of writing it: if some_value do_something end It's a core expectation of the language that !!nil_thing == false, so why violate it?
- Confusion 15y ago
  Because when you write if !some_value do_something end you often don't actually want it to be executed when some_value is nil instead of false. And when it is, you go scratching your head and searching where some_value came from, to discover some silly typo. In some ways, the reverse is even worse: when you write if some_value do_something end and you change some_value from nil to some sensible default like '', you will forget to update this clause and you will not understand why the code is being executed. If you use if !some_value.nil? do_something end you don't have that problem, because the nil-test sticks out like a sore thumb.
  - csallen 15y ago
    I agree with aphyr's response to you. This has never been a problem for me. I think your issue is that you consider an empty string to be a sensible default representing false or nil.
    - Confusion 15y ago
      I fully agree that those sane defaults indeed aren't right for representing false or nil. What I'm arguing is rather the reverse: nil is often initially used as an (insane?) default and that is later changed without updating all related checks (because they don't stick out and demand attention, which makes them easy to overlook or 'overthink'), which causes bugs.
  - aphyr 15y ago
    I disagree. I find it most natural to assume nil and false are negatively charged because that's how the language is defined. If I want to differentiate between nil and false, I use .nil? or == false. Somehow this has never been a problem for me in eight years and hundreds of thousands of Ruby lines--but every programmer is different, and I'd like to hear other views. change the base case of some_value from nil to 0, nil to NullObject change some_value from nil to some sensible default like '' What, what, what are you doing? Who uses an empty string to mean "uninitialized"? Nil and {0, "", etc) have very different semantic meanings. How would you discriminate between the default "" and a user-submitted ""? If you mean to check whether it has changed from the default, compare it to a default constant. If you mean to check emptiness, use #empty? or #blank?. I read these kinds of explicit .nil? checks as fighting the language, and in some ways, a violation of the cultural contract in Ruby and Lisp around truth charge.
- perfunctory 15y ago
  I actually agree with Confusion. All these implicit coercions _will_ bite you. Don't understand why his post is downvoted.
anonymoushn 15y ago
If the language ships with falsy nils, I don't think it's unreasonable to assume that nil values are also falsy.
schukin 15y ago
You probably shouldn't use 'nil' to mean 'false', but since pretty much every compiler / interpreter out there will take the same branch when given a condition that's either nil or false, I'd say it's much safer to stick w/ what's existed for decades rather than accommodate some sort of tri-state boolean.
- Confusion 15y ago
  Well, the tri-state boolean was a worst-case, but consistent, example. I did mention you should hardly ever need that ;)
riffraff 15y ago
IME using any value as boolean never caused me any problem, neither in ruby nor in other languages where the same is possible. What stuff should happen when something is unexpectedly nil if you tested it for truth-ishnes? Once you have written if not some_value something with some_value end the only things you can do with `x` are things you can do with `false`, which are not many.
- Confusion 15y ago
  See my response to necubi. The main problem is the reverse: if some_value something with some_value end where you first use nil to signal false, but later change the base case of some_value from nil to 0, nil to NullObject or nil to some other base value. Since you think of these base cases as 'nothing', you will forget to change this related conditional the first time around, because it seems it would still do the right thing.
jbert 15y ago
By the same argument, nil != true. This could lead to a tri-state ifs (with true/false/nil branches). Or you can just consider that 2-branch 'if' runs the first branch if the test expr is true and the second 'otherwise'. (So that doesn't make nil false, it just makes it non-true). And then your interpretation and everyone else co-exists and we can all code together.

necubi 15y ago

Such code is everywhere in the Ruby community and explicitly endorsed by many. I have never seen code like your second example in the wild, and it's far more complicated than the idiomatic way of writing it: if some_value do_something end It's a core expectation of the language that !!nil_thing == false, so why violate it?

Confusion 15y ago
Because when you write if !some_value do_something end you often don't actually want it to be executed when some_value is nil instead of false. And when it is, you go scratching your head and searching where some_value came from, to discover some silly typo. In some ways, the reverse is even worse: when you write if some_value do_something end and you change some_value from nil to some sensible default like '', you will forget to update this clause and you will not understand why the code is being executed. If you use if !some_value.nil? do_something end you don't have that problem, because the nil-test sticks out like a sore thumb.
- csallen 15y ago
  I agree with aphyr's response to you. This has never been a problem for me. I think your issue is that you consider an empty string to be a sensible default representing false or nil.
  - Confusion 15y ago
    I fully agree that those sane defaults indeed aren't right for representing false or nil. What I'm arguing is rather the reverse: nil is often initially used as an (insane?) default and that is later changed without updating all related checks (because they don't stick out and demand attention, which makes them easy to overlook or 'overthink'), which causes bugs.
- aphyr 15y ago
  I disagree. I find it most natural to assume nil and false are negatively charged because that's how the language is defined. If I want to differentiate between nil and false, I use .nil? or == false. Somehow this has never been a problem for me in eight years and hundreds of thousands of Ruby lines--but every programmer is different, and I'd like to hear other views. change the base case of some_value from nil to 0, nil to NullObject change some_value from nil to some sensible default like '' What, what, what are you doing? Who uses an empty string to mean "uninitialized"? Nil and {0, "", etc) have very different semantic meanings. How would you discriminate between the default "" and a user-submitted ""? If you mean to check whether it has changed from the default, compare it to a default constant. If you mean to check emptiness, use #empty? or #blank?. I read these kinds of explicit .nil? checks as fighting the language, and in some ways, a violation of the cultural contract in Ruby and Lisp around truth charge.
perfunctory 15y ago
I actually agree with Confusion. All these implicit coercions _will_ bite you. Don't understand why his post is downvoted.

anonymoushn 15y ago

If the language ships with falsy nils, I don't think it's unreasonable to assume that nil values are also falsy.

schukin 15y ago

You probably shouldn't use 'nil' to mean 'false', but since pretty much every compiler / interpreter out there will take the same branch when given a condition that's either nil or false, I'd say it's much safer to stick w/ what's existed for decades rather than accommodate some sort of tri-state boolean.

Confusion 15y ago
Well, the tri-state boolean was a worst-case, but consistent, example. I did mention you should hardly ever need that ;)

riffraff 15y ago

IME using any value as boolean never caused me any problem, neither in ruby nor in other languages where the same is possible. What stuff should happen when something is unexpectedly nil if you tested it for truth-ishnes? Once you have written if not some_value something with some_value end the only things you can do with `x` are things you can do with `false`, which are not many.

Confusion 15y ago
See my response to necubi. The main problem is the reverse: if some_value something with some_value end where you first use nil to signal false, but later change the base case of some_value from nil to 0, nil to NullObject or nil to some other base value. Since you think of these base cases as 'nothing', you will forget to change this related conditional the first time around, because it seems it would still do the right thing.

jbert 15y ago

By the same argument, nil != true. This could lead to a tri-state ifs (with true/false/nil branches). Or you can just consider that 2-branch 'if' runs the first branch if the test expr is true and the second 'otherwise'. (So that doesn't make nil false, it just makes it non-true). And then your interpretation and everyone else co-exists and we can all code together.