Ruby 方法和可选参数 [英] Ruby Methods and Optional parameters

问题描述

我正在使用 Ruby on Rails，我正在尝试创建一个带有可选参数的方法.显然有很多方法可以做到.我尝试将可选参数命名为散列，而不定义它们.输出不同.看一看:

I'm playing with Ruby on Rails and I'm trying to create a method with optional parameters. Apparently there are many ways to do it. I trying naming the optional parameters as hashes, and without defining them. The output is different. Take a look:

# This functions works fine!
def my_info(name, options = {})
    age = options[:age] || 27
    weight = options[:weight] || 160
    city = options[:city] || "New York"
    puts "My name is #{name}, my age is #{age}, my weight is #{weight} and I live in {city}"
end


my_info "Bill"
-> My name is Bill, my age is 27, my weight is 160 and I live in New York
-> OK!

my_info "Bill", age: 28
-> My name is Bill, my age is 28, my weight is 160 and I live in New York
-> OK!

my_info "Bill", weight: 200
-> My name is Bill, my age is 27, my weight is 200 and I live in New York
-> OK!

my_info "Bill", city: "Scottsdale"
-> My name is Bill, my age is 27, my weight is 160 and I live in Scottsdale
-> OK!

my_info "Bill", age: 99, weight: 300, city: "Sao Paulo"
-> My name is Bill, my age is 99, my weight is 300 and I live in Sao Paulo
-> OK!

****************************

# This functions doesn't work when I don't pass all the parameters
def my_info2(name, options = {age: 27, weight: 160, city: "New York"})
    age = options[:age]
    weight = options[:weight]
    city = options[:city]
    puts "My name is #{name}, my age is #{age}, my weight is #{weight} and I live in #{city}"
end

my_info2 "Bill"
-> My name is Bill, my age is 27, my weight is 160 and I live in New York
-> OK!

my_info2 "Bill", age: 28
-> My name is Bill, my age is 28, my weight is  and I live in 
-> NOT OK! Where is my weight and the city??

my_info2 "Bill", weight: 200
-> My name is Bill, my age is , my weight is 200 and I live in 
-> NOT OK! Where is my age and the city??

my_info2 "Bill", city: "Scottsdale"
-> My name is Bill, my age is , my weight is  and I live in Scottsdale
-> NOT OK! Where is my age and my weight?

my_info2 "Bill", age: 99, weight: 300, city: "Sao Paulo"
-> My name is Bill, my age is 99, my weight is 300 and I live in Sao Paulo
-> OK!

可选参数的第二种方法有什么问题?第二种方法仅在我不传递任何可选参数或全部传递时才有效.

What's wrong with the second approach for optional parameters? The second method only works if I don't pass any optional parameter or if I pass them all.

我错过了什么?

推荐答案

可选参数在 ruby​​ 中的工作方式是指定一个等号，如果没有传递参数 那么你指定的是用过的.因此，如果在第二个示例中没有传递第二个参数，则

The way optional arguments work in ruby is that you specify an equal sign, and if no argument is passed then what you specified is used. So, if no second argument is passed in the second example, then

{age: 27, weight: 160, city: "New York"}

被使用.如果您确实在第一个参数之后使用了散列语法，则传递 exact 散列.

is used. If you do use the hash syntax after the first argument, then that exact hash is passed.

你能做的最好的是

def my_info2(name, options = {})
  options = {age: 27, weight: 160, city: "New York"}.merge(options)
...

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