pointers - What does => (equals greater than) mean in Fortran? -

-

i'm looking through old fortran 90 code , have come across => symbol:

var => item

it looks it's being used sort of assignment.

searching google "arrow symbol fortran" or "equals greater symbol fortran" gives me no related material.

=> appears in 6 contexts syntactic element in modern fortran, most, not all, related pointers: pointer assignment; pointer initialization; procedure (pointer) declaration; type-bound procedure declaration; association; renaming. there close connection between of these. loosely, in many => can viewed providing alternative temporary or permanent means of referencing entity. in none, however, => acting operator.1

pointer assignment

pointer assignment 1 of traditional appearances of =>, appearing in fortran 90. used associate pointer target, , explained in another answer.

use association renaming

renaming of entities use associated involves element => , other appearance in fortran 90/95 code. such use statements like

use mod_a, c=>a use mod_b, : cc => bb

following such use statement module entities a , bb known local names c , cc.

pointer initialization

pointer initialization pointer assignment => appears. pointer initialization defines initial pointer association of pointer. see in statements such as

real, target :: real, pointer :: b=>a real, pointer :: c=>null()

with explicit initializtion, pointer b here associated a , pointer c unassociated. these 2 forms helpful in modern fortran in in fortran 90 pointer starts life of undefined association status. here know b , c have defined pointer association status, , can use associated.

for derived type components such syntax gives default initialization.

procedure declaration

much explicit/default initialization data objects => features in defining initial association of procedure pointer.

procedure(proc_interface), pointer :: proc1 => donkey procedure(proc_interface), pointer :: proc2 => null()

here, proc1 again associated procedure donkey , can have such things as

call proc1(...)

much when proc1 pointer assigned donkey outside declaration statement. proc2 is, expected, not associated.

as data object components of derived types => can feature in setting initial association of object-bound procedure

type   procedure(proc_interface), pointer :: proc => donkey end type

type-bound procedure declaration

conceptually related above use of => in declaring type-bound procedures.

type  contains   procedure :: proc => donkey   generic :: assignment(=) => type_a_eq end type

here in type a proc binding name b%proc (for b entity of type a) procedure reference. also, through type_a_eq, have defined assignment entities of type a on left-hand side.

association

=> appears in couple of association contexts. associate , select type constructs associate name selector.

associate (a => 1+2)   ... ! in block have entity named end associate

and

class(*) b select type (a => b)   type (real)     ... ! non-polymorphic real here end select

these associations differ pointers. a in associate block needn't (and in example above isn't) variable.

[1] concept of operator precisely defined in fortran language, such in 3.2.4 of fortran 2008 specification. unlike many other languages, assignment (with =) not operation, statement. in c-like languages can have (a=b) expression returning result: not case in fortran. same holds pointer assignment in fortran. other cases above wholly distinct idea of assignment. in fortran, = appearing in initialization not same thing assignment. => cannot viewed having 1 effect.


Comments

Post a Comment

Popular posts from this blog

yii2 - Yii 2 Running a Cron in the basic template -

-
i have seen instructions on running cron in advanced template, cant figure out how on basic template. have following controller in basic controllers folder. <?php namespace app\controllers; use yii\console\controller; /** * cron controller */ class croncontroller extends controller { public function actionindex() { echo "cron service runnning"; } public function actionmail($to) { echo "sending mail " . $to; } } i have navigated root of application , tried these comands yii cron php yii cron im getting unknown comand "cron" i know old question failed find actual answer this. if @ code yii exec file you'll notice requires /common/config/aliases.php file console/config/main.php. can naturally change these or copy on these advanced template. hope solves problem wanting same thing.
Read more

asp.net - 'System.Web.HttpContext' does not contain a definition for 'GetOwinContext' Mystery -

-
i realize question might seem trivial some, it's these types of things find myself fighting quite bit , want make sense of despite seeming losing battle in .net (for me anyway). so, if following: using system.web; ... applicationuser user = system.web.httpcontext.getowincontext().getusermanager<applicationusermanager>().findbyid(system.web.httpcontext.user.identity.getuserid()); that produces error in title , red getowincontext() , error cannot resolve symbol 'getowincontext()' however, if following (remove system.web in front of httpcontext ), works expected (or @ least no errors): using system.web; ... applicationuser user = httpcontext.getowincontext().getusermanager<applicationusermanager>().findbyid(system.web.httpcontext.user.identity.getuserid()); however, if (same line that's working using system.web commented out): //using system.web; ... applicationuser user = httpcontext.getowincontext().getusermana...
Read more

android - Crash when clicking button with custom theme -

-
i creating custom theme button , using android:onclick event of button xml handle click of button. due reason crashing below exception java.lang.illegalstateexception: not find method myonclick(view) in activity class android.view.contextthemewrapper onclick handler on view class android.widget.button id 'button1' and working fine if remove theme attribute button, below theme button <style name="buttontheme" parent="@android:style/widget.button"> <item name="android:textcolor">#ff0000</item> <item name="android:shadowcolor">#ff000000</item> </style> and button defined in xml below, <button android:id="@+id/button1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_below="@+id/textview1" android:layout_margin="20dp" android...
Read more