inheritance - Can a structure inherit from a class in .NET? -

-

i confused inheritance in .net , here why.

i of understanding structure cannot inherit class in .net, example, following won't compile:

struct mystruct : myclass {  }

but today read integers (and other value types) structs , not objects , inherit valuetype class. valuetype class inherits system.object , purpose override methods in system.object make these methods suitable value types.

so what's deal? can structure inherit class in .net, can not or can in circumstances?

thanks

within guts of .net, definition struct containing members same definition class same fields , members, , inherits system.valuetype. note compilers not allow 1 declare class inherits valuetype, when 1 declares struct, compiler, "behind scenes" declares class does.

what makes value types special in .net way run-time allocates storage locations (variables, fields, parameters, etc.) when storage location of type not inheriting valuetype declared, runtime allocate space heap object reference. contrast, when storage location of type inheriting valuetype declared, runtime allocate space public , private fields of type. type int, system allocates private field of special primitive type, outside normal type system.

note storage location of value type doesn't hold instance of type; instead is instance of type, , holds of fields of type. statement struct1 = struct2 not replace value-type instance struct1 instance struct2. instead, copies of fields struct2 on corresponding fields in struct1. likewise if value-type storage location passed method procedure without using ref keyword, passed not struct instance itself, rather contents of fields.

if necessary copy value-type storage location 1 of type not derived valuetype (e.g. object or icomparable), system create new heap-object instance of value type, copy fields value type new instancen , store reference new instance in target storage location. process called "boxing". compilers implicitly, attempting behave though value type storage location holds object derives valuetype. it's important note, though, illusion. if type x derives y, 1 has x named xx , y named yy, , 1 performs xx = yy, such statement should cause xx , yy refer same object instance. happen if xx , yy types not derived valuetype, if yy holds instance of derived valuetype. not happen, however, if xx and/or yy derives valuetype. in case, system copy fields 1 instance (possibly new) instance.


Comments

Post a Comment

Popular posts from this blog

django - How can I change user group without delete record -

-
on website user have 1 group. , user can change group. it's made user.groups.clear() and user.groups.add(new_group) but it's not efficient, because there 2 sql query: delete, insert. how can change group update query? user , group related each other using manytomanyfield . means intersection table exists relating both entities, , if don't specify model map (using through attribute) django creates 1 you. looking @ sources django.contrib.auth.models see that's case. fortunatly, can access intermediary model using through attribute of manager (in case, user.groups.through ). can use regular model. example: >>> alice = user.objects.create_user('alice', 'alice@example.com', 'alicepw') >>> employee = group.objects.create(name='employee') >>> manager = group.objects.create(name='manager') >>> alice.groups.add(employee) >>> alice.groups.all() [<group: employee...
Read more

java - Need to add SOAP security token -

-
i need set custom soap header attribute on jax-ws generated webservice client. case webservice calls must go through proxy server requiring specific token (recieved web request header) present in soap request header. e.g.: 1 carserviceservice service = null; 2 service = new carserviceservice(new url(url), new qname(qname); 3 carserviceendpoint port = service.getcarserviceport(); it seems in line 3 wsdl retrieved , call fails due missing security token. 1 point direction on how done? a detailed example has been mentioned here: creating , deploying jax-ws web service on tomcat 6 this article shows how create , use security token .
Read more

java - EclipseLink JPA Object is not a known entity type -

-
i have strange problem eclipselink , object want persist. have 1 object (keypointlistimpl) stores object keypointimpl in list. persisting keypointimpl objects works great if try persist keypointlistimpl object java.lang.illegalargumentexception says object keypointimpl isn't known entity type. here keypointimpl code: @entity @table(name="keypoints") public class keypointimpl implements keypoint { @id @generatedvalue(strategy = generationtype.identity) private int id; @enumerated(enumtype.string) private detectortype keypointtype; private float x; private float y; private float size; private float angle; private float response; private int octave; private int classid; ... } here keypointlistimpl code: @entity @table(name="keypointlists") public class keypointlistimpl implements keypointlist { @id @generatedvalue(strategy = generationtype.identity) private int id; @onetoone(cascade={ca...
Read more