Overview

Both checkboxes and switches use the .custom-control class as a wrapper. They also both use <input type="checkbox"> and have a <label> with a class of .custom-control-label. Switches add the .custom-switch class to their .custom-control wrapper.

<div class="form-group">
  <div class="custom-control custom-switch">
    <input type="checkbox" checked class="custom-control-input" id="exampleSwitch1">
    <label class="custom-control-label" for="exampleSwitch1">Switch</label>
  </div>
  <div class="custom-control custom-switch">
    <input type="checkbox" class="custom-control-input" id="exampleSwitch2">
    <label class="custom-control-label" for="exampleSwitch2">Switch</label>
  </div>
  <div class="custom-control custom-switch">
    <input type="checkbox" disabled checked class="custom-control-input" id="exampleSwitch3">
    <label class="custom-control-label" for="exampleSwitch3">Disabled</label>
  </div>
  <div class="custom-control custom-switch">
    <input type="checkbox" disabled class="custom-control-input" id="exampleSwitch4">
    <label class="custom-control-label" for="exampleSwitch4">Disabled</label>
  </div>
</div>

Inline

<div class="form-group">
  <div class="custom-control custom-switch custom-control-inline mr-4">
    <input type="checkbox" checked class="custom-control-input" id="exampleSwitchInline1">
    <label class="custom-control-label" for="exampleSwitchInline1">Switch</label>
  </div>
  <div class="custom-control custom-switch custom-control-inline mr-4">
    <input type="checkbox" class="custom-control-input" id="exampleSwitchInline2">
    <label class="custom-control-label" for="exampleSwitchInline2">Switch</label>
  </div>
  <div class="custom-control custom-switch custom-control-inline mr-4">
    <input type="checkbox" disabled checked class="custom-control-input" id="exampleSwitchInline3">
    <label class="custom-control-label" for="exampleSwitchInline3">Disabled</label>
  </div>
  <div class="custom-control custom-switch custom-control-inline mr-4">
    <input type="checkbox" disabled class="custom-control-input" id="exampleSwitchInline4">
    <label class="custom-control-label" for="exampleSwitchInline4">Disabled</label>
  </div>
</div>