What is the difference between ::: and :::.() in scala -

-

in scala list class shown that:

list(1, 2) ::: list(3, 4) = list(3, 4).:::(list(1, 2)) = list(1, 2, 3, 4). shouldn't:

list(1,2) ::: list(3,4) = list(1,2).:::(list(3,4)) = list(3,4,1,2)

( method ::: prefixes list)

from docs:

def :::(prefix: list[a]): list[a]

[use case] adds elements of given list in front of list.

example:

list(1, 2) ::: list(3, 4) = list(3, 4).:::(list(1, 2)) = list(1, 2, 3, 4)

in scala, operators end in : right associative , invoking object appears on right side of operator. because right associative, prefix method called on object "to right", list(3, 4).

then name says, prefix list(3, 4) list(1, 2), , that's why list(1, 2, 3 ,4). not intuitive thing in world it's this:

a ::: b // ending in :, flip argument order, call method on b. b .:: // :: = prefix b result = a(concatenated) b

now let's @ right hand side:

list(3, 4).:::(list(1, 2))

the . dot performing inversion of ::: prefixed invocation, invert 2 list objects before performing ::: prefix operation.

list(3, 4).:::(list(1,2)) = list(1, 2) ::: list(3, 4) // above. // , it's same story.

the . dot way invert associative operators. a ::: b same b .::: a


Comments

Post a Comment

Popular posts from this blog

java - Jmockit String final length method mocking Issue -

-
using jmockit 1.2 jar, trying mock string's length method getting unexpected invocation exception: failed: test java.lang.illegalstateexception: missing invocation mocked type @ point; please make sure such invocations appear after declaration of suitable mock field or parameter @ stringdemo.testa$1.<init>(testa.java:17) @ stringdemo.testa.test(testa.java:13) i using testng: @test public void test() throws exception { new expectations() { @mocked("length") string astring; { astring.length(); result = 2; } }; system.out.println(a.showa("test")); } } actual class a: public class { public static int showa(string str){ int a= str.length(); return a; } } this wrong way of recording expected results. shouldn't mock , record string's length() method, record showa() instead. here solution @suppresswarnings("unused...
Read more

What is the difference between data design and data model(ERD) -

-
i have google question , find answer in day. know, data design many many table have list column,and mark pk , fk. why er-diagram have find this? data design process of designing database. main output of data design detailed logical data model of database. some people data design includes of needed logical , physical design choices , physical storage parameters needed generate design in data definition language. technically, database analysis, database analysts (dbas) trained do. while person can both data design , database analysis, these 2 different tasks. data design models data. database analysis takes model , applies 1 or more database engines (relational, hierarchical, nosql). a logical data model 1 of main outputs of data design. data model represented entity relationship diagram, or er diagram.
Read more

ios - Can NSManagedObject conform to NSCoding -

-
i need transfer single object across device. right converting nsmanagedobject dictionary , archiving , sending nsdata. upon receiving unarchiving it. transfer nsmanagedobject archiving , unarchiving instead of creating intermediate data object. @interface test : nsmanagedobject<nscoding> @property (nonatomic, retain) nsstring * title; @end @implementation test @dynamic title; - (id)initwithcoder:(nscoder *)coder { self = [super init]; if (self) { self.title = [coder decodeobjectforkey:@"title"]; //<crash } return self; } - (void)encodewithcoder:(nscoder *)coder { [coder encodeobject:self.title forkey:@"title"]; } @end nsdata *archivedobjects = [nskeyedarchiver archiveddatawithrootobject:testobj]; nsdata *objectsdata = archivedobjects; if ([objectsdata length] > 0) { nsarray *objects = [nskeyedunarchiver unarchiveobjectwithdata:objectsdata]; } the problem above code is. crashes @ self.title in initwithcoder sa...
Read more