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I started to put print-statements throughout my code. So as not to clutter up the output, I did something like:
dputs LEVEL, "string"
where LEVEL is 0 for errors, 1 for important .. 5 for verbose and is compared to DEBUG_LEVEL. Now my problem is, that in a statement like:
dputs 5, "#{big_class.inspect}"
the string is always evaluated, also if I set DEBUG_LEVEL to 1. And this evaluation can take a long time. My favourite solution would be something like:
dputs 5, '#{big_class.inspect}'
and then evaluate the string if desired. But I don't manage to get the string in a form I can evaluate. So the only think I could come up with is:
dputs( 5 ){ "#{big_class.inspect}" }
but this looks just ugly. So how can I evaluate a '#{}' string?
You could do this by having dputs use sprintf (via %). That way it can decide not to build the interpolated string unless it knows it's going to print it:
def dputs(level, format_str, *vars)
puts(format_str % vars) if level <= LEVEL
end
LEVEL = 5
name = 'Andrew'
dputs 5, 'hello %s', name
#=> hello Andrew
Or, as you suggest, you can pass a block which would defer the interpolation till the block actually runs:
def dputs(level, &string)
raise ArgumentError.new('block required') unless block_given?
puts string.call if level <= LEVEL
end
I think it's of no value whatsoever, but I just came up with:
2.3.1 :001 > s = '#{a}'
=> "\#{a}"
2.3.1 :002 > a = 1
=> 1
2.3.1 :003 > instance_eval s.inspect.gsub('\\', '')
=> "1"
2.3.1 :004 > s = 'Hello #{a} and #{a+1}!'
=> "Hello \#{a} and \#{a+1}!"
2.3.1 :005 > instance_eval s.inspect.gsub('\\', '')
=> "Hello 1 and 2!"
Don't use that in production :)
I don't think you can dodge the ugly there. The interpolation happens before the call to dputs unless you put it inside a block, which postpones it until dputs evaluates it. I don't know where dputs comes from, so I'm not sure what its semantics are, but my guess is the block would get you the lazy evaluation you want. Not pretty, but it does the job.
OK, obviously I was just too lazy. I thought there must be a more clean way to do this, Ruby being the best programming language and all ;) To evaluate a string like
a = '#{1+1} some text #{big_class.inspect}'
only when needed, I didn't find a better way than going through the string and eval all "#{}" encountered:
str = ""
"#{b}\#{}".scan( /(.*?)(#\{[^\}]*\})/ ){
str += $1
str += eval( $2[2..-2] ).to_s
}
if you're not into clarity, you can get rid of the temporary-variable str:
"#{b}\#{}".scan( /(.*?)(#\{[^\}]*\})/ ).collect{|c|
c[0] + eval( c[1][2..-2] ).to_s
}.join
The String.scan-method goes through every '#{}'-block, as there might be more than one, evaluating it (the 2..-2 cuts out the "#{" and "}") and putting it together with the rest of the string.
For the corner-case of the string not ending with a '#{}'-block, an empty block is added, just to be sure.
But well, after being some years in Ruby, this still feels clunky and C-ish. Perhaps it's time to learn a new language!
When programming ruby I always find myself doing this:
a = [a, b].min
This means compare a and b and store the smallest value in a. I don't like writing the code above as I have to write a twice.
I know that some non-standard dialects of C++ had an operator which did exactly this
a <?= b
Which I find very convenient. But I'm not really interested in the operator as much as I'm in the feature of avoiding repetition. I would also be happy if I could write
a.keep_max(b)
a can be a quite long variable, like my_array[indice1][indice2], and you don't want to write that twice.
I did alot of googling on this and found no result, hopefully this question will pop up and be useful for others aswell.
So, is there any non-repeitive way to express what I want in ruby?
What you would like to do is in fact not possible in ruby (see this question). I think the best you can do is
def max(*args)
args.max
end
a = max a, b
I don't understand your question. You can always do something like this ...
module Comparable
def keep_min(other)
(self <=> other) <= 0 ? self : other
end
def keep_max(other)
(self <=> other) >= 0 ? self : other
end
end
1.keep_min(2)
=> 1
1.keep_max(2)
=> 2
Well, that won't work for all objects with <=> because not all of them are implementing Comparable, so you could monkey-patch Object.
Personally I prefer clarity and tend to avoid monkey-patching. Plus, this clearly is a binary predicate, just like "+", therefore method-chaining doesn't necessarily make sense so I prefer something like this to get rid of that array syntax:
def min(*args)
args.min
end
def max(*args)
args.max
end
min(1, 2)
=> 1
max(1, 2)
=> 2
But hey, I'm also a Python developer :-)
You can define your own method for it:
class Object
def keep_max(other)
[self, other].max
end
end
a = 3
b = 7
puts a.keep_max(b)
But you should be careful defining methods on Object as it can have unpredictable behaviour (for example, if objects cannot be compared).
def keep_max(var, other, binding)
eval "#{var} = [#{var}, #{other}].max", binding
end
a = 5
b = 78
keep_max(:a, :b, binding)
puts a
#=> 78
This basically does what you want. Take a look at Change variable passed in a method
I often have a situation where I want to do some conditional logic and then return a part of the condition. How can I do this without repeating the part of the condition in the true or false expression?
For example:
ClassName.method.blank? ? false : ClassName.method
Is there any way to avoid repeating ClassName.method?
Here is a real-world example:
PROFESSIONAL_ROLES.key(self.professional_role).nil? ?
948460516 : PROFESSIONAL_ROLES.key(self.professional_role)
Assuming you're okay with false being treated the same way as nil, you use ||:
PROFESSIONAL_ROLES.key(self.professional_role) || 948460516
This will return 948460516 if key returns nil or false and the return value of the call to key otherwise.
Note that this will only return 948460516 if key returns nil or false, not if it returns an empty array or string. Since you used nil? in your second example, I assume that's okay. However you used blank? in the first example (and blank? returns true for empty arrays and strings), so I'm not sure.
If you just want to DRY, then you can use a temp variable:
x = ClassName.method
x.blank? ? false : x
x = PROFESSIONAL_ROLES.key(self.professional_role)
x.nil? ? 948460516 : x
If you don't want to use a temp variable, you can use a block:
Proc.new do |x| x.blank? ? false : x end.call(ClassName.method)
Proc.new do |x| x.nil? ? 948460516 : x end.call(PROFESSIONAL_ROLES.key(self.professional_role))
For the cases you describe (where you just want to use the original value when a default-check fails), it'd be straightforward to write a helper method:
def x_or_default(x, defval, checker = :nil?)
if x.send(checker) then defval else x end
end
x_or_default(ClassName.method, false, :blank?)
x_or_default(PROFESSIONAL_ROLES.key(self.professional_role), 94840516)
which is very similar to the || method described, but would also work with your blank? example.
I usually use temporary variables for this sort of thing.
I know this doesn't look too pretty, but it does make things a bit DRYer.
a = "ABC"
b = (temp = a.downcase).length < 3 ? "---" : temp
If you don't want to create temp variable for whatever reason, you could reuse something that already exists like $_.
How can I get the opposite of a boolean in Ruby (I know that it is converted to 0/1) using a method inline?
say I have the given instance:
class Vote
def return_opposite
self.value
end
end
Which obviously doesn't do anything, but I can't seem to find a method that is simple and short something like opposite() or the like. Does something like this exist and I'm just not looking at the right place in the docs? If one doesn't exist is there a really short ternary that would toggle it from 1 => 0 or 0 => 1?
I like to use this
#object.boolean = !#object.boolean
Boolean expressions are not 0 or 1 in Ruby, actually, 0 is not false
If n is numeric we are swapping 0 and 1...
n == 0 ? 1 : 0 # or...
1 - n # or...
[1, 0][n] # or maybe [1, 0][n & 1] # or...
class Integer; def oh_1; self==0 ? 1:0; end; end; p [12.oh_1, 0.oh_1, 1.oh_1] # or...
n.succ % 2 # or...
n ^= 1
If b already makes sense as a Ruby true or false conditional, it's going to be hard to beat:
!b
These examples differ in how they treat out-of-range input...
You can use XOR operator (exclusive or)
a = true
a # => true
a ^= true
a # => false
a ^= true
a # => true
Edit: See comment by #philomory below.
I believe this is basically an oversight in the boolean classes (TrueClass and FalseClass) in Ruby.
You can negate any object:
nil.! => true
false.! => true
true.! => false
0.! => false
1.! => false
a.! => false (all other objects)
But you cannot in-place negate the boolean objects:
a.!! => does not compile
I guess this would call for trouble with the compiler's grammar.
The best you can do, is thus:
a = a.!
If you just want to access the opposite of the value, use ! as some people have said in the comments. If you want to actually change the value, that would be bool_value = !bool_value. Unless I've misunderstood your question. Which is quite possible.
In order to toggle a boolean data in rails you can do this vote.toggle!(:boolean)
If you want to toggle boolean (that is false and true) , that would be as simple as just use ! as others has stated.
If you want to toggle between 0 and 1 , I can only think of something naive as below :)
def opposite
op = {0=>1,1=>0}
op[self.value]
end
In a Rails app, I use this method to toggle a post between paused and active, so ! (not) is my preferred method.
def toggle
#post = Post.find(params[:id])
#post.update_attributes paused: !#post.paused?
msg = #post.paused? ? 'The post is now paused.' : 'The post is now active.'
redirect_to :back, notice: msg
end
I think that using a ternary can be interesting :
check = false
check == true ? check = false : check = true
I am looking for a concise way to check a value to see if it is nil or zero. Currently I am doing something like:
if (!val || val == 0)
# Is nil or zero
end
But this seems very clumsy.
Objects have a nil? method.
if val.nil? || val == 0
[do something]
end
Or, for just one instruction:
[do something] if val.nil? || val == 0
From Ruby 2.3.0 onward, you can combine the safe navigation operator (&.) with Numeric#nonzero?. &. returns nil if the instance was nil and nonzero? - if the number was 0:
unless val&.nonzero?
# Is nil or zero
end
Or postfix:
do_something unless val&.nonzero?
If you really like method names with question marks at the end:
if val.nil? || val.zero?
# do stuff
end
Your solution is fine, as are a few of the other solutions.
Ruby can make you search for a pretty way to do everything, if you're not careful.
First off I think that's about the most concise way you can check for that particular condition.
Second, to me this is a code smell that indicates a potential flaw in your design. Generally nil and zero shouldn't mean the same thing. If possible you should try to eliminate the possibility of val being nil before you hit this code, either by checking that at the beginning of the method or some other mechanism.
You might have a perfectly legitimate reason to do this in which case I think your code is good, but I'd at least consider trying to get rid of the nil check if possible.
You can use the Object.nil? to test for nil specifically (and not get caught up between false and nil). You can monkey-patch a method into Object as well.
class Object
def nil_or_zero?
return (self.nil? or self == 0)
end
end
my_object = MyClass.new
my_object.nil_or_zero?
==> false
This is not recommended as changes to Object are difficult for coworkers to trace, and may make your code unpredictable to others.
nil.to_i returns zero, so I often do this:
val.to_i.zero?
However, you will get an exception if val is ever an object that does not respond_to #to_i.
I believe your code is incorrect; it will in fact test for three values: nil, false, and zero. This is because the !val expression is true for all values that are false, which in Ruby is nil and false.
The best I can come up with right now is
if val == nil || val == 0
# do stuff
end
Which of course is not very clever, but (very) clear.
My solution also use Refinements, minus the conditionals.
module Nothingness
refine Numeric do
alias_method :nothing?, :zero?
end
refine NilClass do
alias_method :nothing?, :nil?
end
end
using Nothingness
if val.nothing?
# Do something
end
Short and clear
[0, nil].include?(val)
Shortest and best way should be
if val&.>(0)
# do something
end
For val&.>(0)
it returns nil when val is nil since > basically is also a method, nil equal to false in ruby. It return false when val == 0.
Rails does this via attribute query methods, where in addition to false and nil, 0 and "" also evaluate to false.
if (model.attribute?) # => false if attribute is 0 and model is an ActiveRecord::Base derivation
However it has its share of detractors. http://www.joegrossberg.com/archives/002995.html
To be as idiomatic as possible, I'd suggest this.
if val.nil? or val == 0
# Do something
end
Because:
It uses the nil? method.
It uses the "or" operator, which is preferable to ||.
It doesn't use parentheses, which are not necessary in this case. Parentheses should only be used when they serve some purpose, such as overriding the precedence of certain operators.
I deal with this by defining an "is?" method, which I can then implement differently on various classes. So for Array, "is?" means "size>0"; for Fixnum it means "self != 0"; for String it means "self != ''". NilClass, of course, defines "is?" as just returning nil.
You can use case if you like:
case val with nil, 0
# do stuff
end
Then you can use anything that works with ===, which is nice sometimes. Or do something like this:
not_valid = nil, 0
case val1 with *not_valid
# do stuff
end
#do other stuff
case val2 with *not_valid, false #Test for values that is nil, 0 or false
# do other other stuff
end
It's not exactly good OOP, but it's very flexible and it works. My ifs usually end up as cases anyway.
Of course Enum.any?/Enum.include? kind of works too ... if you like to get really cryptic:
if [0, nil].include? val
#do stuff
end
The right thing to do is of course to define a method or function. Or, if you have to do the same thing with many values, use a combination of those nice iterators.
I really like Rails blank? method for that kind of things, but it won't return true for 0. So you can add your method:
def nil_zero?
if respond_to?(:zero?)
zero?
else
!self
end
end
And it will check if some value is nil or 0:
nil.nil_zero?
=> true
0.nil_zero?
=> true
10.nil_zero?
=> false
if val.nil_zero?
#...
end
Instead of monkey patching a class, you could use refinements starting in Ruby 2.1. Refinements are similar to monkey patching; in that, they allow you to modify the class, but the modification is limited to the scope you wish to use it in.
This is overkill if you want to do this check once, but if you are repeating yourself it's a great alternative to monkey patching.
module NilOrZero
refine Object do
def nil_or_zero?
nil? or zero?
end
end
end
using NilOrZero
class Car
def initialize(speed: 100)
puts speed.nil_or_zero?
end
end
car = Car.new # false
car = Car.new(speed: nil) # true
car = Car.new(speed: 0) # true
Refinements were changed in the last minute to be scoped to the file. So earlier examples may have shown this, which will not work.
class Car
using NilOrZero
end
This is very concise:
if (val || 0) == 0
# Is nil, false, or zero.
end
It works as long as you don't mind treating false the same as nil. In the projects I've worked on, that distinction only matters once in a while. The rest of the time I personally prefer to skip .nil? and have slightly shorter code.
[Update: I don't write this sort of thing any more. It works but is too cryptic. I have tried to set right my misdeeds by changing the few places where I did it.]
By the way, I didn't use .zero? since this raises an exception if val is, say, a string. But .zero? would be fine if you know that's not the case.
This evaluates to true for nil and zero: nil.to_s.to_d == 0
unless (val || 0).zero?
# do stufff
end
In a single stretch you can do this:
[do_something] if val.to_i == 0
nil.to_i will return 0
Another solution:
if val.to_i == 0
# do stuff
end
val ||= 0
if val == 0
# do something here
end