Ruby case when表達(dá)式實(shí)際應(yīng)用解析

作者：佚名 2009-12-15 09:43:50

我們在這篇文章中為大家介紹的是有關(guān)Ruby case when表達(dá)式的一些基本使用技巧。比如是否能夠在Groovy中得到支持等。

Ruby語言中存在著許多表達(dá)式，這些表達(dá)式用法不盡相同，實(shí)現(xiàn)的功能也不同。熟練的掌握這些表達(dá)式的用法，可以有助于我們編程的方便性。今天看到有人在Groovy的郵件列表上問Groovy能不能支持Ruby case when表達(dá)式： #t#

Ruby case when表達(dá)式代碼示例：

car = "Patriot"
manufacturer = case car
when "Focus": "Ford"
when "Navigator": "Lincoln"
when "Camry": "Toyota"
when "Civic": "Honda"
when "Patriot": "Jeep"
when "Jetta": "VW"
when "Ceyene": "Porsche"
when "Outback": "Subaru"
when "520i": "BMW"
when "Tundra": "Nissan"
else "Unknown"
end
puts "The " + car + " is made by
" + manufacturer
car = "Patriot"
manufacturer = case car
when "Focus": "Ford"
when "Navigator": "Lincoln"
when "Camry": "Toyota"
when "Civic": "Honda"
when "Patriot": "Jeep"
when "Jetta": "VW"
when "Ceyene": "Porsche"
when "Outback": "Subaru"
when "520i": "BMW"
when "Tundra": "Nissan"
else "Unknown"
end
puts "The " + car + " is made by
" + manufacturer

然后Guillaume給出了這么一段Ruby case when表達(dá)式代碼：

def car = "Patriot"   
def manufacturer = match(car) {   
when "Focus", "Ford"   
when "Navigator", "Lincoln"   
when "Camry", "Toyota"   
when "Civic", "Honda"   
when "Patriot", "Jeep"   
when "Jetta", "VW"   
when "Ceyene", "Porsche"   
when "Outback", "Subaru"   
when "520i", "BMW"   
when "Tundra", "Nissan"   
otherwise "Unknown"   
}   
println "The $car is made by 
$manufacturer"   
def match(obj, closure) {   
closure.subject = obj   
closure.when = { value, result ->   
if (value == subject)   
throw new MatchResultException
(result: result)   
}   
closure.otherwise = { return it }   
closure.resolveStrategy = 
Closure.DELEGATE_FIRST   
try {   
closure()   
closure.otherwise()   
} catch (MatchResultException r) {   
r.result   
}   
}   
class MatchResultException
 extends RuntimeException {   
def result   
}   
def car = "Patriot" 
def manufacturer = match(car) {  
when "Focus", "Ford"  
when "Navigator", "Lincoln"  
when "Camry", "Toyota"  
when "Civic", "Honda"  
when "Patriot", "Jeep"  
when "Jetta", "VW"  
when "Ceyene", "Porsche"  
when "Outback", "Subaru"  
when "520i", "BMW"  
when "Tundra", "Nissan"  
otherwise "Unknown"  
}  
println "The $car is made 
by $manufacturer"  
def match(obj, closure) {  
closure.subject = obj 
closure.when = { value, result -> 
if (value == subject)  
throw new MatchResultException
(result: result)  
}  
closure.otherwise = { return it }  
closure.resolveStrategy = 
Closure.DELEGATE_FIRST  
try {  
closure()  
closure.otherwise()  
} catch (MatchResultException r) {  
r.result  
}  
}  
class MatchResultException 
extends RuntimeException {  
def result  
}

我不是很喜歡里面用異常來控制程序的流程，而且覺得“when "Focus", "Ford"”中間的逗號不夠直觀，因此就在上面的Ruby case when表達(dá)式代碼的基礎(chǔ)上做了一些修改：

def match(subject, closure) {   
def whenMap = [:], otherwise = null   
closure.when = { map -> whenMap.putAll(map) }   
closure.otherwise = { otherwise = it }   
closure.resolveStrategy = Closure.DELEGATE_FIRST   
closure()   
def result = whenMap.find { condition, 
value -> subject in condition }   
return result ? result.value : otherwise   
}   
def manufacturer(car) {   
match(car) {   
when "Focus": "Ford"   
when "Navigator": "Lincoln"   
when "Camry": "Toyota"   
when "Civic": "Honda"   
when "Patriot": "Jeep"   
when "Jetta": "VW"   
when "Ceyene": "Porsche"   
when "Outback": "Subaru"   
when "520i": "BMW"   
when "Tundra": "Nissan"   
otherwise "Unknown"   
}   
}   
println "The Patriot is made
 by ${manufacturer('Patriot')}"   
println "The QQ is made by $
{manufacturer('QQ')}"   
def match(subject, closure) {  
def whenMap = [:], otherwise = null 
closure.when = { map -> whenMap.putAll(map) }  
closure.otherwise = { otherwise = it }  
closure.resolveStrategy = Closure.
DELEGATE_FIRST  
closure()  
def result = whenMap.find { condition, 
value -> subject in condition }  
return result ? result.value : otherwise  
}  
def manufacturer(car) {  
match(car) {  
when "Focus": "Ford"  
when "Navigator": "Lincoln"  
when "Camry": "Toyota"  
when "Civic": "Honda"  
when "Patriot": "Jeep"  
when "Jetta": "VW"  
when "Ceyene": "Porsche"  
when "Outback": "Subaru"  
when "520i": "BMW"  
when "Tundra": "Nissan"  
otherwise "Unknown"  
}  
}  
println "The Patriot is made
 by ${manufacturer('Patriot')}"  
println "The QQ is made by $
{manufacturer('QQ')}"

以上Ruby case when表達(dá)式代碼在Groovy 1.6下編譯通過。

責(zé)任編輯：曹凱來源： javaeye.com

Ruby case when表達(dá)式