In VB, i have different behaviour with DirectCast and casting into value type (double, int, …) depending of the number of indirection<\/p>\n
DirectCast(nothing, Double)\n<\/code><\/pre>\nreturn 0<\/p>\n
But, if i try to cast something like a element of a matrix equals to nothing, there is an exception<\/p>\n
Dim pArray as Object() = { nothing, 1.5, 2.27, -3.0}\nDirectCast(pArray(1), Double) 'work with no issue\nDirectCast(pArray(0), Double) 'Exception : Cannot convert to double\n<\/code><\/pre>\nIn the same way :<\/p>\n
Dim TestCasting as object = nothing\nDirectcast(TestCasting, double) 'Exception : Cannot convert to double \n<\/code><\/pre>\nHow can i make so the directcast of pArray(0) work the same way than DirectCast(nothing, double) ?<\/p>\n
EDIT : My post was an example that highlight the issue without any concerns for the rest of the code.<\/p>\n
To be thrill. here is an exemple that could pose some issue. Let’s take a random table (no primary key or anything but nevermind) :<\/p>\n
TABLE [dbo].[IDENTIFICATION] (\n [USER_ID] INT IDENTITY (1, 1) NOT NULL,\n [PASSWORD] NVARCHAR(50) NULL,\n [EXPIRATION_D] DATETIME NOT NULL,\n [LAYOUT] INT NULL,\n);\n<\/code><\/pre>\nNow, i have a method who return a Objec(,)<\/p>\n
Dim pArray as Object(,) = myconnection.GetSqlRequest(\"Select USER_ID, PASSWORD, EXPIRATION_D, LAYOUT from IDENTIFICATION where USER_ID = 3\")\n<\/code><\/pre>\nthis may return something like { 3, “StackOverflow”, New Date(2110,01,01), nothing} because layout is an optional field.<\/p>\n
I can do as such :<\/p>\n
if pArray(0,3) is nothing then\n Layout = 0\nElse \n Layout = DirectCast(pArray(0,3), Double)\nEnd if\n<\/code><\/pre>\nBut my goal would be to just do :<\/p>\n
Layout = DirectCast(pArray(0,3))\n<\/code><\/pre>\nmostly because i’m refactoring a huge part of a code i didn’t write and also because it bugs me that DirectCast(nothing, Double) return 0 except in this case.<\/p>\n
\n- \n
That’s simple: don’t use Nothing<\/code> when you store Doubles<\/code> in an array and don’t use a Object()<\/code> when you actually want to store doubles.<\/p>\nWait, it would be better to use a Double?()<\/code> anyway. Nullables can be initialized with null\/Nothing<\/code> Then you don’t need a cast at all.<\/p>\nDim pArray As Double?() = {Nothing, 1.5, 2.27, -3.0}\nDim first = pArray(0)\nIf first.HasValue Then\n ' No, it's a Nullable(Of Double)\/Double? without a value\nEnd If\n<\/code><\/pre>\nEdit<\/strong> According to your original question. The better question would be why this works in VB:<\/p>\nDim d as Double = DirectCast(Nothing, Double) ' => 0.0\n<\/code><\/pre>\nThe reason: Nothing<\/code> in VB.Net is the equivalent of default(T)<\/code> in C#: the default value for the given type which is 0 for numeric types, Date.MinValue<\/code> for Date<\/code> and Nothing<\/code>(now in the meaning of null<\/code> in C#) for reference types.<\/p>\nSo DirectCast(Nothing, Double)<\/code> will be converted implicitely to the Double<\/code> 0. Whereas the Object()<\/code> contains really objects which is a placeholder for everything. But Nothing<\/code> is normally a “unknown” state of any object and not a double, so the DirectCast<\/code> which is very strict fails. It would also throw a runtime error if you would change the value -3.0<\/code> to -3<\/code> since that is actually an Integer<\/code>.<\/p>\nTo cut a long story short,<\/p>\n
use CType<\/code> instead of DirectCast<\/code> for those conversions and it’ll work.<\/strong><\/p>\nDim obj As Object() = {Nothing, 1.0, 2}\nDim d1 = CType(obj(0), Double) ' => 0.0\nDim d2 = CType(obj(1), Double) ' => 1.0\nDim d3 = CType(obj(2), Double) ' => 2.0\n<\/code><\/pre>\n<\/li>\n<\/ol>\nOriginally posted 2013-11-09 20:29:46. <\/small><\/p>","protected":false},"excerpt":{"rendered":"
In VB, i have different behaviour with DirectCast and casting into value type (double, int, …) depending of the number of indirection DirectCast(nothing, Double) return 0 But, if i try to cast something like a element of a matrix equals to nothing, there is an exception Dim pArray as Object() = { nothing, 1.5, 2.27, […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-539","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts\/539","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/comments?post=539"}],"version-history":[{"count":0,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts\/539\/revisions"}],"wp:attachment":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/media?parent=539"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/categories?post=539"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/tags?post=539"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}