diff --git a/core/lib/Drupal/Core/Entity/Plugin/DataType/EntityReference.php b/core/lib/Drupal/Core/Entity/Plugin/DataType/EntityReference.php
index a59f7d1..74f25b4 100644
--- a/core/lib/Drupal/Core/Entity/Plugin/DataType/EntityReference.php
+++ b/core/lib/Drupal/Core/Entity/Plugin/DataType/EntityReference.php
@@ -64,8 +64,7 @@ public function getTarget() {
     if (!isset($this->target) && isset($this->id)) {
       // If we have a valid reference, return the entity object which is typed
       // data itself.
-      $constraints = $this->definition->getConstraints();
-      $this->target = entity_load($constraints['EntityType'], $this->id);
+      $this->target = entity_load($this->definition->getConstraint('EntityType'), $this->id);
     }
     return $this->target;
   }
diff --git a/core/lib/Drupal/Core/Field/FieldDefinition.php b/core/lib/Drupal/Core/Field/FieldDefinition.php
index d33da70..e93006d 100644
--- a/core/lib/Drupal/Core/Field/FieldDefinition.php
+++ b/core/lib/Drupal/Core/Field/FieldDefinition.php
@@ -22,7 +22,7 @@ class FieldDefinition extends ListDefinition implements FieldDefinitionInterface
    * @param string $type
    *   The type of the field.
    *
-   * @return \Drupal\Core\Field\FieldDefinition
+   * @return \Drupal\Core\Field\FieldDefinitionInterface
    *   A new field definition object.
    */
   public static function create($type) {
@@ -42,7 +42,7 @@ public function getFieldName() {
    * @param string $name
    *   The field name to set.
    *
-   * @return self
+   * @return static
    *   The object itself for chaining.
    */
   public function setFieldName($name) {
@@ -73,7 +73,7 @@ public function getFieldSettings() {
    * @param array $settings
    *   The value to set.
    *
-   * @return self
+   * @return static
    *   The object itself for chaining.
    */
   public function setFieldSettings(array $settings) {
@@ -85,8 +85,7 @@ public function setFieldSettings(array $settings) {
    * {@inheritdoc}
    */
   public function getFieldSetting($setting_name) {
-    $settings = $this->getFieldSettings();
-    return isset($settings[$setting_name]) ? $settings[$setting_name] : NULL;
+    return $this->getItemDefinition()->getSetting($setting_name);
   }
 
   /**
@@ -97,13 +96,12 @@ public function getFieldSetting($setting_name) {
    * @param mixed $value
    *   The value to set.
    *
-   * @return self
+   * @return static
    *   The object itself for chaining.
    */
   public function setFieldSetting($setting_name, $value) {
-    $settings = $this->getFieldSettings();
-    $settings[$setting_name] = $value;
-    return $this->setFieldSettings($settings);
+    $this->getItemDefinition()->setSetting($setting_name, $value);
+    return $this;
   }
 
   /**
@@ -126,7 +124,7 @@ public function isFieldTranslatable() {
    * @param bool $translatable
    *   Whether the field is translatable.
    *
-   * @return self
+   * @return static
    *   The object itself for chaining.
    */
   public function setTranslatable($translatable) {
@@ -191,7 +189,7 @@ public function isFieldMultiple() {
    * @param bool $required
    *   Whether the field is required.
    *
-   * @return self
+   * @return static
    *   The object itself for chaining.
    */
   public function setFieldRequired($required) {
@@ -211,7 +209,7 @@ public function isFieldQueryable() {
    * @param bool $queryable
    *   Whether the field is queryable.
    *
-   * @return self
+   * @return static
    *   The object itself for chaining.
    */
   public function setFieldQueryable($queryable) {
@@ -227,7 +225,7 @@ public function setFieldQueryable($queryable) {
    * @param array $constraints
    *   The constraints to set.
    *
-   * @return self
+   * @return static
    *   The object itself for chaining.
    */
   public function setPropertyConstraints($name, array $constraints) {
diff --git a/core/lib/Drupal/Core/Field/FieldItemBase.php b/core/lib/Drupal/Core/Field/FieldItemBase.php
index c329ed6..0145489 100644
--- a/core/lib/Drupal/Core/Field/FieldItemBase.php
+++ b/core/lib/Drupal/Core/Field/FieldItemBase.php
@@ -199,7 +199,7 @@ public function getConstraints() {
     // applying them.
     if ($property_constraints = $this->definition->getConstraints()) {
       $constraints[] = \Drupal::typedData()->getValidationConstraintManager()
-        ->create('ComplexData', $property_constraints);
+        ->create('ComplexData', $property_constraints['ComplexData']);
     }
     return $constraints;
   }
diff --git a/core/lib/Drupal/Core/TypedData/DataDefinition.php b/core/lib/Drupal/Core/TypedData/DataDefinition.php
index ed4709e..9fec1a3 100644
--- a/core/lib/Drupal/Core/TypedData/DataDefinition.php
+++ b/core/lib/Drupal/Core/TypedData/DataDefinition.php
@@ -202,12 +202,7 @@ public function setClass($class) {
   }
 
   /**
-   * Returns the array of settings, as required by the used class.
-   *
-   * See the documentation of the class for supported or required settings.
-   *
-   * @return array
-   *   The array of settings.
+   * {@inheritdoc}
    */
   public function getSettings() {
     return isset($this->definition['settings']) ? $this->definition['settings'] : array();
@@ -228,6 +223,29 @@ public function setSettings(array $settings) {
   }
 
   /**
+   * {@inheritdoc}
+   */
+  public function getSetting($setting_name) {
+    return isset($this->definition['settings'][$setting_name]) ? $this->definition['settings'][$setting_name] : NULL;
+  }
+
+  /**
+   * Sets a definition setting.
+   *
+   * @param string $setting_name
+   *   The definition setting to set.
+   * @param mixed $value
+   *   The value to set.
+   *
+   * @return static
+   *   The object itself for chaining.
+   */
+  public function setSetting($setting_name, $value) {
+    $this->definition['settings'][$setting_name] = $value;
+    return $this;
+  }
+
+  /**
    * Returns an array of validation constraints.
    *
    * See \Drupal\Core\TypedData\TypedDataManager::getConstraints() for details.
@@ -241,6 +259,13 @@ public function getConstraints() {
   }
 
   /**
+   * {@inheritdoc}
+   */
+  public function getConstraint($constraint_name) {
+    return isset($this->definition['constraints'][$constraint_name]) ? $this->definition['constraints'][$constraint_name] : NULL;
+  }
+
+  /**
    * Sets the array of validation constraints.
    *
    * See \Drupal\Core\TypedData\TypedDataManager::getConstraints() for details.
diff --git a/core/lib/Drupal/Core/TypedData/DataDefinitionInterface.php b/core/lib/Drupal/Core/TypedData/DataDefinitionInterface.php
index eb5dd67..219cd30 100644
--- a/core/lib/Drupal/Core/TypedData/DataDefinitionInterface.php
+++ b/core/lib/Drupal/Core/TypedData/DataDefinitionInterface.php
@@ -102,6 +102,17 @@ public function getClass();
   public function getSettings();
 
   /**
+   * Returns the value of a given setting.
+   *
+   * @param string $setting_name
+   *   The setting name.
+   *
+   * @return mixed
+   *   The setting value.
+   */
+  public function getSetting($setting_name);
+
+  /**
    * Returns an array of validation constraints.
    *
    * See \Drupal\Core\TypedData\TypedDataManager::getConstraints() for details.
@@ -112,4 +123,17 @@ public function getSettings();
    */
   public function getConstraints();
 
+  /**
+   * Returns a validation constraint.
+   *
+   * See \Drupal\Core\TypedData\TypedDataManager::getConstraints() for details.
+   *
+   * @param string $constraint_name
+   *   The name of the the constraint, i.e. its plugin id.
+   *
+   * @return \Symfony\Component\Validator\Constraint
+   *   A validation constraint.
+   */
+  public function getConstraint($constraint_name);
+
 }
diff --git a/core/lib/Drupal/Core/TypedData/TypedDataManager.php b/core/lib/Drupal/Core/TypedData/TypedDataManager.php
index 1045697..65db76b 100644
--- a/core/lib/Drupal/Core/TypedData/TypedDataManager.php
+++ b/core/lib/Drupal/Core/TypedData/TypedDataManager.php
@@ -188,10 +188,12 @@ public function getInstance(array $options) {
    */
   public function getPropertyInstance(TypedDataInterface $object, $property_name, $value = NULL) {
     $definition = $object->getRoot()->getDefinition();
-    $key = $definition->getDataType();
+    // If the definition is a list, we need to look at the data type and the
+    // settings of its item definition.
     if ($definition instanceof ListDefinition) {
-      $key .= ':' . $definition->getItemDefinition()->getDataType();
+      $definition = $definition->getItemDefinition();
     }
+    $key = $definition->getDataType();
     if ($settings = $definition->getSettings()) {
       $key .= ':' . implode(',', $settings);
     }
diff --git a/core/modules/edit/lib/Drupal/edit/Form/EditFieldForm.php b/core/modules/edit/lib/Drupal/edit/Form/EditFieldForm.php
index ad9410d..909e0a3 100644
--- a/core/modules/edit/lib/Drupal/edit/Form/EditFieldForm.php
+++ b/core/modules/edit/lib/Drupal/edit/Form/EditFieldForm.php
@@ -243,8 +243,8 @@ protected function simplify(array &$form, array &$form_state) {
    */
   protected function getChangedFieldName(EntityInterface $entity) {
     foreach ($entity as $field_name => $field) {
-      $definition = $field->getDefinition();
-      if (isset($definition['property_constraints']['value']['EntityChanged'])) {
+      $constraints = $field->getDefinition()->getConstraints();
+      if (isset($constraints['ComplexData']['value']['EntityChanged'])) {
         return $field_name;
       }
     }
diff --git a/core/modules/field/lib/Drupal/field/Entity/Field.php b/core/modules/field/lib/Drupal/field/Entity/Field.php
index fc52346..0483272 100644
--- a/core/modules/field/lib/Drupal/field/Entity/Field.php
+++ b/core/modules/field/lib/Drupal/field/Entity/Field.php
@@ -782,6 +782,18 @@ public function getSettings() {
   /**
    * {@inheritdoc}
    */
+  public function getSetting($setting_name) {
+    // This should actually return the settings for field item list, which are
+    // not the field settings. However, there is no harm in returning field
+    // settings here, so we do that to avoid confusion for now.
+    // @todo: Unify with getFieldSettings() or remove once typed data moved
+    // to the adapter approach.
+    return $this->getFieldSetting($setting_name);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function getConstraints() {
     return array();
   }
@@ -789,6 +801,13 @@ public function getConstraints() {
   /**
    * {@inheritdoc}
    */
+  public function getConstraint($constraint_name) {
+    return NULL;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function getItemDefinition() {
     if (!isset($this->itemDefinition)) {
       $this->itemDefinition = DataDefinition::create('field_item:' . $this->type)
diff --git a/core/modules/field/lib/Drupal/field/Entity/FieldInstance.php b/core/modules/field/lib/Drupal/field/Entity/FieldInstance.php
index 7e34d3d..3b63fa9 100644
--- a/core/modules/field/lib/Drupal/field/Entity/FieldInstance.php
+++ b/core/modules/field/lib/Drupal/field/Entity/FieldInstance.php
@@ -677,6 +677,13 @@ public function getSettings() {
   /**
    * {@inheritdoc}
    */
+  public function getSetting($setting_name) {
+    return $this->getFieldSetting($setting_name);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function getConstraints() {
     return array();
   }
@@ -684,6 +691,13 @@ public function getConstraints() {
   /**
    * {@inheritdoc}
    */
+  public function getConstraint($constraint_name) {
+    return NULL;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function getItemDefinition() {
     if (!isset($this->itemDefinition)) {
       $this->itemDefinition = DataDefinition::create('field_item:' . $this->field->type)
diff --git a/core/modules/text/lib/Drupal/text/Plugin/Field/FieldType/TextItemBase.php b/core/modules/text/lib/Drupal/text/Plugin/Field/FieldType/TextItemBase.php
index ef42c2f..a41b77a 100644
--- a/core/modules/text/lib/Drupal/text/Plugin/Field/FieldType/TextItemBase.php
+++ b/core/modules/text/lib/Drupal/text/Plugin/Field/FieldType/TextItemBase.php
@@ -76,7 +76,7 @@ public function getCacheData() {
     $text_processing = $this->getFieldSetting('text_processing');
     if (!$text_processing || filter_format_allowcache($this->get('format')->getValue())) {
       foreach ($this->getPropertyDefinitions() as $property => $definition) {
-        if (isset($definition['class']) && ($definition['class'] == '\Drupal\text\TextProcessed')) {
+        if ($definition->getClass() == '\Drupal\text\TextProcessed') {
           $data[$property] = $this->get($property)->getValue();
         }
       }
@@ -96,8 +96,7 @@ public function onChange($property_name) {
     // Unset processed properties that are affected by the change.
     foreach ($this->getPropertyDefinitions() as $property => $definition) {
       if ($definition->getClass() == '\Drupal\text\TextProcessed') {
-        $settings = $definition->getSettings();
-        if ($property_name == 'format' || (isset($settings['text source']) && $settings['text source'] == $property_name)) {
+        if ($property_name == 'format' || ($definition->getSetting('text source') == $property_name)) {
           $this->set($property, NULL, FALSE);
         }
       }
diff --git a/core/modules/text/lib/Drupal/text/TextProcessed.php b/core/modules/text/lib/Drupal/text/TextProcessed.php
index 22a0772..e32087b 100644
--- a/core/modules/text/lib/Drupal/text/TextProcessed.php
+++ b/core/modules/text/lib/Drupal/text/TextProcessed.php
@@ -32,8 +32,7 @@ class TextProcessed extends TypedData {
   public function __construct(DataDefinitionInterface $definition, $name = NULL, TypedDataInterface $parent = NULL) {
     parent::__construct($definition, $name, $parent);
 
-    $settings = $definition->getSettings();
-    if (!isset($settings['text source'])) {
+    if ($definition->getSetting('text source') === NULL) {
       throw new \InvalidArgumentException("The definition's 'source' key has to specify the name of the text property to be processed.");
     }
   }
@@ -47,8 +46,7 @@ public function getValue($langcode = NULL) {
     }
 
     $item = $this->getParent();
-    $settings = $this->definition->getSettings();
-    $text = $item->{($settings['text source'])};
+    $text = $item->{($this->definition->getSetting('text source'))};
 
     // Avoid running check_markup() or check_plain() on empty strings.
     if (!isset($text) || $text === '') {