c# - Using Elvis operator in combination with string.Equals -

-

i wonder why following code works in c# 6.0:
(in example data random class containing val public string)

if ("x".equals(data.val?.tolower()) { }

but following line isn't:

if (data.val?.tolower().equals("x")) { }

visual studio shows me following error:

cannot implicitly convert type 'bool?' 'bool'. explicit conversion exists (are missing cast?)

if ("x".equals(data.val?.tolower()) { }

will return boolean because of equals call this:

if (data.val?.tolower().equals("x")) { }

when expression evaluated return system.nullable<bool> different bool (former struct can assigned value null while latter can true or false) the if expects. also, in c# null value doesn't evaluate false (according c# specification).


Comments

Post a Comment

Popular posts from this blog

php - Invalid Cofiguration - yii\base\InvalidConfigException - Yii2 -

-
Image
i've installed yii2-user module/dektrium yii2-app-basic application command composer require "dektrium/yii2-user:0.9.*@dev" config/console.php return [ . . 'modules' => [ 'gii' => 'yii\gii\module', 'user' => [ 'class' => 'dektrium\user\module', ], ], . . ] config/web.php 'components' => [ . . /* 'user' => [ 'identityclass' => 'app\models\user', 'enableautologin' => true, ], */ 'modules' => [ 'user' => [ 'class' => 'dektrium\user\module', ], ], . . ] after that, run command $ php yii migrate/up --migrationpath=@vendor/dektrium/yii2-user/migrations updating database schema . but, when run http://localhost/mylawsuit/yii/web/index.php?r=u
Read more

How to show in django cms breadcrumbs full path? -

-
need advice - how show in breadcrumbs whole path article or page? i've got code: {% ance in ancestors %} <li> {% if not forloop.last %} <a href="{{ ance.get_absolute_url }}">{{ ance.get_menu_title }}</a> {% else %} <span class="active">{{ ance.get_menu_title }}</span> {% endif %} </li> {% endfor %} but shows "home" , current page. how modify show whole path in breadcrumbs? i've found in file menu_tags.py code calls ancestors. @ least there class showbreadcrumbs: class showbreadcrumb(inclusiontag): """ shows breadcrumb node has same url current request - start level: after level should breadcrumb start? 0=home - template: template used render breadcrumb """ name = 'show_breadcrumb' template = 'menu/dummy.html' options = options( argument('start_level', default=0, require
Read more

ruby on rails - npm error: tunneling socket could not be established, cause=connect ETIMEDOUT -

-
i have app uses rails framework , implements angularjs part of front end. i have pushed heroku , have heroku toolbelt installed, when try migrate db using "heroku run rake db:migrate" receive following error(s): installing core plugins heroku-cli-addons, heroku-apps, heroku-fork, heroku-git, heroku-local, heroku-run, heroku-status... error installing package. try running again gode_debug=info see more output. ! `run` not heroku command. ! perhaps meant `-h`, `2fa`, `auth`, `join`, `open`, `orgs`, `pg`, `ps` or `rake`. ! see `heroku help` list of available commands. i run command "gode_debug=info heroku run rake db:migrate" , receive error: npm err! darwin 14.5.0 npm err! argv "/users/christopher_pelnar/.heroku/node-v4.2.1-darwin-x64/bin/node" "/users/christopher_pelnar/.heroku/node-v4.2.1-darwin-x64/lib/node_modules/npm/cli.js" "install" "heroku-cli-addons" "heroku-apps" "heroku-fork
Read more