c# - Nullable <= vs == comparison result -

-

this behaviour sounds wrong me.

datetime? birth = null; datetime? death = null;  console.writeline(birth == death); // true console.writeline(birth <= death); // false

why so? incredibly strange. of course mean why second expression not evaluate true well.

edit:

i understand following comparisons return false, because cannot said how relate each other:

console.writeline(birth < death); // false console.writeline(birth > death); // false

this understandable behaviour. but... @ logic:

  • <= means < or ==
  • we don't know how read < - true or false
  • we know == true
  • since 1 of conditions true, other condition cannot untrue result. logic or, not and.

my point true or else should true.

i know c# team designed way, intuition different. since smart people have written c# such rules, want learn why intuition wrong here :)

i understand not looking specs explanation of why nullables designed way.

to remove ambiguity, designers have let these operators return bool? value instead of bool value null in case 1 of operands null.

but if had made choice, code like: 

bool? comparison = birth <= death;  if (comparison.hasvalue && comparison.value) { }

which bit cumbersome.

as side note, seems like, looking @ il, c# compiler generates comparison default values first , checks if 1 of operands null seems bit odd...

.method private hidebysig static void  main(string[] args) cil managed {   .locals init ([0] valuetype [mscorlib]system.nullable`1<int32> x,            [1] valuetype [mscorlib]system.nullable`1<int32> v_1,            [2] valuetype [mscorlib]system.nullable`1<int32> v_2)   il_0000:  ldloca.s   x   il_0002:  ldc.i4.1   il_0003:  call       instance void valuetype [mscorlib]system.nullable`1<int32>::.ctor(!0)   il_0008:  ldc.i4.2   il_0009:  newobj     instance void valuetype [mscorlib]system.nullable`1<int32>::.ctor(!0)   il_000e:  ldloc.0   il_000f:  stloc.1   il_0010:  stloc.2   il_0011:  ldloca.s   v_1   il_0013:  call       instance !0 valuetype [mscorlib]system.nullable`1<int32>::getvalueordefault()   il_0018:  ldloca.s   v_2   il_001a:  call       instance !0 valuetype [mscorlib]system.nullable`1<int32>::getvalueordefault()   il_001f:  ble.s      il_0024   il_0021:  ldc.i4.0   il_0022:  br.s       il_0033   il_0024:  ldloca.s   v_1   il_0026:  call       instance bool valuetype [mscorlib]system.nullable`1<int32>::get_hasvalue()   il_002b:  ldloca.s   v_2   il_002d:  call       instance bool valuetype [mscorlib]system.nullable`1<int32>::get_hasvalue()   il_0032:  ,   il_0033:  brfalse.s  il_003a   il_0035:  call       void [mscorlib]system.console::writeline()   il_003a:  ret } // end of method program::main

it replicating logic present in static nullable class.


Comments

Post a Comment

Popular posts from this blog

qt - Using float or double for own QML classes -

-
i've created components , helper methods using c++ , qt used in qml gui. of methods calculate gui elements (size, transformations, scene graph items creation). target arm 32 bit using opengl / eglfs render output. opengl using float , qml using real (defined double ). what should use in c++ do not lose precision? if use qreal ( double ) shouldn't lose precision. if git grep float in qtbase.git , can find out bit more: dist/changes-5.2.0-**************************************************************************** dist/changes-5.2.0-* important behavior changes * dist/changes-5.2.0-**************************************************************************** dist/changes-5.2.0- dist/changes-5.2.0- - qt compiled qreal typedef'ed double on dist/changes-5.2.0: platforms. qreal float on arm chipsets before. guarantees more dist/changes-5.2.0- consistent behavior between platforms qt supports, binary dist/chan...
Read more

Create Outlook appointment via C# .Net -

-
i need create outlook appointment using microsoft.office.interop.outlook , while can work locally on own workstation , works if run web application via server's browser, not work when connect server externally. hence, think might permission issue. i changed application pool identity " localsystem " don't access denied error. unfortunately, doesn't work. the app behaves if appointment created, appointment doesn't appear in outlook. here include file on top of aspx.cs page using outlook = microsoft.office.interop.outlook; here code using pop appointment. outlook.application apptapp = new outlook.application(); outlook.appointmentitem appt = apptapp.createitem(outlook.olitemtype.olappointmentitem) outlook.appointmentitem; appt.subject = txtfirstname.text + " " + txtlastname.text; appt.body = txtcomment.text; appt.alldayevent = false; appt.start = datetime.parse(txtreminderdate.text + " 8:00 am"); appt.end = datetime.p...
Read more

ios - Swift Array Resetting Itself -

-
i have 2 arrays: pointhistory , datehistory . have nstimer , , when timer runs out, action called. in action appending int pointhistory , , current date string datehistory . here timer action: func timeraction() { let steppervalue = int(stepper.value) employee.numberofpoints = steppervalue networking.saveemployee(employee, completion: { (error) -> void in if error != nil { let alert = uialertcontroller(title: "error", message: "there error updating \(self.employee.name)'s points", preferredstyle: .alert) let alertaction = uialertaction(title: "ok", style: .cancel, handler: nil) alert.addaction(alertaction) self.presentviewcontroller(alert, animated: true, completion: nil) } }) var dateformatter = nsdateformatter() dateformatter.dateformat = "mm-dd-yyyy" dateformatter.timezone = nstimezone.localtimezone() var date = nsdate() var ...
Read more