How can explain the F# type casting output? -


i had problem f# type casting. here code.

type person() =     abstract member sayme : unit -> unit     default u.sayme() = printfn "hi, person." type student() =     inherit person()     override u.sayme() = printfn "hi, student." let x = person()  let x1 = student()  let x2 = x1 :> person  x2.sayme()|>ignore        //***output:"hi, student."

x2 person type. output should "hi, person."

how can explain it?

as others have noticed, override syntax defining virtual members.
speaking, calling virtual method seeing: regardless of upcasts, actual method call found according actual type of object referred to, not type of reference.

this document (msdn) provides more details.

if don't want method virtual, don't use override. way, method in derived class hide parent's method.
here's full code:

type person() =     member u.sayme() = printfn "hi, person." type student() =     inherit person()     member u.sayme() = printfn "hi, student."  let x = student() x.sayme()             // prints "hi, student." (x :> person).sayme() // prints "hi, person."

Comments

Post a Comment

Popular posts from this blog

SPSS keyboard combination alters encoding -

my question not have programming practical issue on spss. accident keyword combination cannot remember because did not intend press changed encoding in spss , text in data in different language english shown small boxes. nevertheless, when kind of analysis performed different language text shown in output. does know reason? tried change encoding did not produce result. first, @ edit > options , see whether setting unicode or locale. might fix it. if have text in multiple languages, want unicode. otherwise, may have specific locale set wrong. can change set locale, need know locale want use.
Read more

Add new record to the table by click on the button in Microsoft Access -

in ms access form want implement separate button, adds new record table. in order added button , attached button event: private sub btnaddrec_click() refresh codecontextobject on error resume next docmd.gotorecord , , acnewrec if err.number <> 0 btnaddrec.enabled = false end if end end sub everything ok when open window , click btnaddrec button, problem when first of perform navigation through existed records , after click on button. got runtime error: 2105: «you can't go specified record. may @ end of recordset» . how solve issue, need have ability add new record on click on specific button, no matter, have walked or not walked through records before. thanks. i created simple form field call description (and autonumber) , created button code follows click event. filled number of records , navigated through them, clicked addnewrec button. form navigated new record without issues. able click addnewrec button directly after
Read more

javascript - jQuery .height() return 0 when visible but non-0 when hidden -

i have problem here right opposite others: in jquery cannot height of element when it's visible, when hidden. have html code: <div id="filtering-filter-holder"> <div id="filtering-filter-holder-inner"></div> </div> basic css it: #filtering-filter-holder { display: none; position: absolute; width: 420px; min-height: 100px; padding: 5px 5px 5px 5px; background-color: #ffffff; border: 1px solid #164372; } and finally, js in document.ready(): $('div.filtering-filter-headline').mouseenter(function() { var el = $(this).parent().find('div.filtering-filter-content'); if ($('div#filtering-filter-holder').is(':visible')) { $('div#filtering-filter-holder-inner').stop(true, true).fadeout(300, function() { $('div#filtering-filter-holder-inner').html($(el).html()); var height = $('div#filtering-filter-holder-inner&#
Read more