Ruby开发技巧

jieforest · 发表于 2013-11-3 00:51

Arrays will be automatically destructured on the right hand side of an assignment, this works particularly nicely when you have a method returning an array.

family, port, host, address = socket.peeraddr

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I’m also partial to this trick for grabbing just the first element of an array.

family, = socket.peeraddr

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jieforest · 发表于 2013-11-3 00:51

However, the same result can be achieved more clearly with #first.

family = socket.peeraddr.first

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You can take advantage of this for Hashes using the #values_at method, which returns an array.

first, last = params.values_at(:first_name, :last_name)

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jieforest · 发表于 2013-11-3 00:52

This implicit destructuring also happens in block arguments.

names = ["Arthur", "Ford", "Trillian"]
ids = [42, 43, 44]
id_names = ids.zip(names) #=> [[42, "Arthur"], [43, "Ford"], [44, "Trillian"]]
id_names.each do |id, name|
puts "user #{id} is #{name}"
end

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Even cooler is you can force further destructuring with parentheses.

id_names = [[42, ["Arthur", "Dent"]], [43, ["Ford", "Prefect"]], [44, ["Tricia", "McMillan"]]]
id_names.each do |id, (first_name, last_name)|
puts "#{id}\t#{last_name}, #{first_name[0]}."
end

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jieforest · 发表于 2013-11-3 00:52

and this works in method parameters!

def euclidean_distance((ax, ay), (bx, by))
Math.sqrt((ax - bx)**2 + (ay - by)**2)
end
euclidean_distance([1, 5], [4, 2]) #=> 4.242640687119285

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Ruby has two methods you can implement for your own classes so that you can take advantage of this. The first to allow an object to be explicitly destructured with * is #to_a.

class Point
attr_accessor :x, :y
def initialize(x, y)
@x, @y = x, y
end
def to_a
[x, y]
end
end
point = Point.new(6, 3)
x, y = *point
x #=> 6
y #=> 3

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jieforest · 发表于 2013-11-3 00:53

The second, for implicit destructuring, is #to_ary. You’ll want to be more selective in implementing this one, as it can lead to your objects suddenly behaving like arrays in places you weren’t expecting.

class Point
attr_accessor :x, :y
def initialize(x, y)
@x, @y = x, y
end
def to_ary
[x, y]
end
end
point = Point.new(6, 3)
x, y = point
x #=> 6
y #=> 3
points = [Point.new(1, 5), Point.new(4, 2)]
points.each do |x, y|
...
end
# using our distance method from an earlier example
euclidean_distance(Point.new(1, 5), Point.new(4, 2)) #=> 4.242640687119285

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jieforest · 发表于 2013-11-5 09:53

There’s one final use for the splat (*); when overriding methods in a subclass and calling super. If it turns out you don’t need the arguments to the method for whatever additional behaviour you’re adding, you can accept all arguments with a bare splat, then a bare super passes all arguments to super.

class LoggedReader < Reader
def initialize(*)
super
@logger = Logger.new(STDOUT)
end
def read(*)
result = super
@logger.info(result)
result
end
end

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jieforest · 发表于 2013-11-5 09:53

Conversion methods

We’ve just seen there are methods for implicit and explicit conversion of an object to an array. These can also be thought of as non-strict and strict conversion methods, and there are a few for other types.

The non-strict methods you probably know well, #to_a, #to_i, #to_s, as of Ruby 2.0 #to_h, and a handful of others. These are available on a wide range of classes, including nil.

{:foo => 1, :bar => 2}.to_a #=> [[:foo, 1], [:bar, 2]]
nil.to_a #=> []
"3".to_i #=> 3
"foo".to_i #=> 0
nil.to_i #=> 0
[1,2,3].to_s #=> "[1, 2, 3]"
nil.to_s #=> ""
nil.to_h #=> {}

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jieforest · 发表于 2013-11-5 09:53

These non-strict conversions can sometimes trip you up, allowing invalid data to pass further down a system than you’d want, returning incorrect results, or producing unexpected errors.

USERS = ["Arthur", "Ford", "Trillian"]
def user(id)
USERS[id.to_i]
end
user(nil) #=> "Arthur" # oops! should have returned an error

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Ruby provides some more strict conversion methods for a few types, #to_ary, #to_int, and #to_str. These are only implemented on classes where the strict conversion makes sense, e.g. #to_int is only available on numeric classes.

def user(id)
USERS[id.to_int]
end
user(nil) #=> NoMethodError: undefined method ‘to_int’ for nil:NilClass

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jieforest · 发表于 2013-11-5 09:54

This makes our example a little better, we’re getting an error and it’s coming from the right place, but the error doesn’t really convey our full intent. Plus the original was probably written that way to allow strings to be used, and as String doesn’t implement #to_int we’ve broken that.

But Ruby has another set of conversion methods, and these are a little more intelligent. The most useful of these areArray() and Integer() (along with the other numeric conversion methods like Float()). String() and Hash() are less useful as they just delegate to #to_s and #to_h.

def user(id)
USERS[Integer(id)]
end
user(nil) #=> TypeError: can't convert nil into Integer

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Now our example raises an error that really shows our intentions, plus we can use strings again. This is where the Integer() method really shines

"1".to_i #=> 1
Integer("1") #=> 1
"foo".to_i #=> 0
Integer("foo") #=> ArgumentError: invalid value for Integer(): "foo"

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jieforest · 发表于 2013-11-5 09:55

Array() is also really useful, as when it can’t convert its argument to an array it will put the argument in an array.

Array([1, 2]) #=> [1, 2]
Array(1) #=> [1]

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Occasionally you want to write a method that takes a single item, or an array of items, and Array() lets you do this without messing about checking types.

def project_cost(hours, developer)
developers = Array(developer)
avg_rate = developers.inject(0) {|acc, d| acc + d.rate} / developers.length
hours * avg_rate
end

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Ruby开发技巧

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