Platform Core Expressions

Table of Contents

• Expression Definitions
  • Identifier
  • Description
  • Configuration Markup
  • Examples
• Common Expressions
  • Identifier
  • Configuration Markup
• Property Testers
  • Identifier
  • Description
  • Configuration Markup
  • Examples

Expression Definitions

Identifier

org.blueberry.core.expressions.definitions

Description

This extension point allows you to create reusable extensions. They can then be used in other core expression constructs. The reference element in a core expression will evaluated the expression definition with the evaluation context that is active for the reference element.

Configuration Markup

<!ELEMENT extension (definition*)>
<!ATTLIST extension
  point CDATA #REQUIRED
  id    CDATA #IMPLIED
  name  CDATA #IMPLIED>

• point: a fully qualified identifier of the target extension point
• id: an optional identifier of the extension instance
• name: an optional name of the extension instance

<!ELEMENT definition (not | and | or | instanceof | test | systemTest | equals | count | with | resolve | adapt | iterate)>
<!ATTLIST definition
  id CDATA #REQUIRED>

Provides a global definition of an expression to be used with the <reference/> expression element. This helps to reuse common expressions.

• id: a globally unique identifier for the expression definition

<!ELEMENT enablement (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>

A generic root element. The element can be used inside an extension point to define its enablement expression. The children of an enablement expression are combined using the and operator.

<!ELEMENT not (not | and | or | instanceof | test | systemTest | equals | count | with | resolve | adapt | iterate | reference)>

This element represent a NOT operation on the result of evaluating it's sub-element expression.

<!ELEMENT and (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>

This element represent an AND operation on the result of evaluating all it's sub-elements expressions.

<!ELEMENT or (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>

This element represent an OR operation on the result of evaluating all it's sub-element expressions.

<!ELEMENT instanceof EMPTY>
<!ATTLIST instanceof
  value CDATA #REQUIRED>

This element is used to perform an instanceof check of the object in focus. The expression returns EvaluationResult.TRUE if the object's type is a sub type of the type specified by the attribute value. Otherwise EvaluationResult.FALSE is returned.

• value: a fully qualified name of a class or interface

<!ELEMENT test EMPTY>
<!ATTLIST test
  property              CDATA #REQUIRED
  args                  CDATA #IMPLIED
  value                 CDATA #IMPLIED
  forcePluginActivation (true | false)>

This element is used to evaluate the property state of the object in focus. The set of testable properties can be extended using the propery tester extension point. The test expression returns EvaluationResult.NOT_LOADED if the property tester doing the actual testing isn't loaded yet and the attribute forcePluginActivation is set to false. If forcePluginActivation is set to true and the evaluation context used to evaluate this expression support plug-in activation then evaluating the property will result in activating the plug-in defining the tester.

• property: The name of an object's property to test.
• args: Additional arguments passed to the property tester. Multiple arguments are seperated by commas. Each individual argument is converted into a Java base type using the same rules as defined for the value attribute of the test expression.
• value: The expected value of the property. Can be omitted if the property is a boolean property. The test expression is supposed to return EvaluationResult.TRUE if the property matches the value and EvaluationResult.FALSE otherwise. The value attribute is converted into a Java base type using the following rules:
  • The string "true" is converted into Boolean.TRUE .
  • The string "false" is converted into Boolean.FALSE .
  • If the string contains a dot then the interpreter tries to convert the value into a Float object. If this fails the string is treated as a java.lang.String.
  • If the string only consists of numbers then the interpreter converts the value in an Integer object.
  • In all other cases the string is treated as a java.lang.String .
  • The conversion of the string into a Boolean , Float , or Integer can be suppressed by surrounding the string with single quotes. For example, the attribute value="'true'" is converted into the string "true".
• forcePluginActivation: A flag indicating whether the plug-in contributing the property tester should be loaded if necessary. As such, this flag should be used judiciously, in order to avoid unnecessary plug-in activations. Most clients should avoid setting this flag to true. This flag is only honored if the evaluation context used to evaluate this expression allows plug-in activation. Otherwise the flag is ignored and no plug-in loading takes place.

<!ELEMENT systemTest EMPTY>
<!ATTLIST systemTest
  property CDATA #REQUIRED
  value    CDATA #REQUIRED>

Tests a system property by calling the System.getProperty method and compares the result with the value specified through the value attribute.

• property: The name of an system property to test.
• value: The expected value of the property. The value is interpreted as a string value.

<!ELEMENT equals EMPTY>
<!ATTLIST equals
  value CDATA #REQUIRED>

This element is used to perform an equals check of the object in focus. The expression returns EvaluationResult.TRUE if the object is equal to the value provided by the attribute value. Otherwise EvaluationResult.FALSE is returned.

• value: The expected value. The value provided as a string is converted into a Java base type using the same rules as for the value attribute of the test expression.

<!ELEMENT count EMPTY>
<!ATTLIST count
  value CDATA #REQUIRED>

This element is used to test the number of elements in a collection.

• value: An expression to specify the number of elements in a list. Following wildcard characters can be used:
  • *: any number of elements
  • ?: no elements or one element
  • +: one or more elements
  • !: no elements
  • integer value: the list must contain the exact number of elements

<!ELEMENT with (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>
<!ATTLIST with
  variable CDATA #REQUIRED>

This element changes the object to be inspected for all its child element to the object referenced by the given variable. If the variable can not be resolved then the expression will throw an ExpressionException when evaluating it. The children of a with expression are combined using the and operator.

• variable: The name of the variable to be used for further inspection. It is up to the evaluator of an extension point to provide the variable in the variable pool.

<!ELEMENT resolve (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>
<!ATTLIST resolve
  variable CDATA #REQUIRED
  args     CDATA #IMPLIED>

This element changes the object to be inspected for all its child element to the object referenced by the given variable. If the variable can not be resolved then the expression will throw an ExpressionException when evaluating it. The children of a with expression are combined using the and operator.

• variable: The name of the variable to be resolved. This variable is then used as the object in focus for child element evaluation. It is up to the evaluator of an extension point to provide a corresponding variable resolver (see berry::IVariableResolver) through the evaluation context passed to the root expression element when evaluating the expression.
• args: Additional arguments passed to the variable resolver. Multiple arguments are seperated by commas. Each individual argument is converted into a Java base type using the same rules as defined for the value attribute of the test expression.

<!ELEMENT adapt (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>
<!ATTLIST adapt
  type CDATA #REQUIRED>

This element is used to adapt the object in focus to the type specified by the attribute type. The expression returns not loaded if either the adapter or the type referenced isn't loaded yet. It throws an ExpressionException during evaluation if the type name doesn't exist at all. The children of an adapt expression are combined using the and operator.

• type: the type to which the object in focus is to be adapted

<!ELEMENT iterate (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>
<!ATTLIST iterate
  operator (or|and)
  ifEmpty  (true | false) >

This element is used to iterate over a variable that is of type java.util.Collection. If the object in focus is not of type java.util.Collection then an ExpressionException will be thrown while evaluating the expression.

• operator: Either "and" or "or". The operator defines how the child elements will be combined. If not specified, "and" will be used.
• ifEmpty: The value return from the iterate expression if the collection is empty. If not specified then true is returned when the operator equals "and" and false is returned if the operator equals "or".

<!ELEMENT reference EMPTY>
<!ATTLIST reference
  definitionId CDATA #REQUIRED>

This element is used to reference an expression from the org.blueberry.core.expressions.definitions extension point. The expression definition will be evaluated within the current expression element using the current evaluation context.

• definitionId: the unique id of an expression from org.blueberry.core.expressions.definitions

Examples

<extension point="org.blueberry.core.expressions.definitions">
  <definition id="com.example.parts.activeProblemsView">
    <with variable="activePartId">
      <equals value="org.blueberry.ui.views.ProblemsView"/>
    </with>
  </definition>
  <definition id="com.example.markers.markerSelection">
    <iterate>
      <instanceof value="org.blueberry.core.resources.IMarker"/>
    </with>
  </definition>
</extension>

Then this expression definition can be used when composing other expressions.

<enabledWhen>
  <reference definitionId="com.example.parts.activeProblemsView">
</enabledWhen>
 
<visibleWhen>
  <and>
    <reference definitionId="com.example.parts.activeProblemsView"/>
    <reference definitionId="com.example.markers.markerSelection"/>
  </and>
</visibleWhen>

Common Expressions

Identifier

org.blueberry.core.expressions.commonExpression

Configuration Markup

<!ELEMENT enablement (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>

A generic root element. The element can be used inside an extension point to define its enablement expression. The children of an enablement expression are combined using the and operator.

<!ELEMENT not (not | and | or | instanceof | test | systemTest | equals | count | with | resolve | adapt | iterate | reference)>

This element represent a NOT operation on the result of evaluating it's sub-element expression.

<!ELEMENT and (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>

This element represent an AND operation on the result of evaluating all it's sub-elements expressions.

<!ELEMENT or (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>

This element represent an OR operation on the result of evaluating all it's sub-element expressions.

<!ELEMENT instanceof EMPTY>
<!ATTLIST instanceof
  value CDATA #REQUIRED>

This element is used to perform an instanceof check of the object in focus. The expression returns EvaluationResult.TRUE if the object's type is a sub type of the type specified by the attribute value. Otherwise EvaluationResult.FALSE is returned.

• value: a fully qualified name of a class or interface

<!ELEMENT test EMPTY>
<!ATTLIST test
  property              CDATA #REQUIRED
  args                  CDATA #IMPLIED
  value                 CDATA #IMPLIED
  forcePluginActivation (true | false) >

This element is used to evaluate the property state of the object in focus. The set of testable properties can be extended using the propery tester extension point. The test expression returns EvaluationResult.NOT_LOADED if the property tester doing the actual testing isn't loaded yet and the attribute forcePluginActivation is set to false. If forcePluginActivation is set to true and the evaluation context used to evaluate this expression support plug-in activation then evaluating the property will result in activating the plug-in defining the tester.

• property: The name of an object's property to test.
• args: Additional arguments passed to the property tester. Multiple arguments are seperated by commas. Each individual argument is converted into a Java base type using the same rules as defined for the value attribute of the test expression.
• value: The expected value of the property. Can be omitted if the property is a boolean property. The test expression is supposed to return EvaluationResult.TRUE if the property matches the value and EvaluationResult.FALSE otherwise. The value attribute is converted into a Java base type using the following rules:
  • The string "true" is converted into Boolean.TRUE
  • The string "false" is converted into Boolean.FALSE
  • If the string contains a dot then the interpreter tries to convert the value into a Float object. If this fails the string is treated as a java.lang.String
  • If the string only consists of numbers then the interpreter converts the value in an Integer object.
  • In all other cases the string is treated as a java.lang.String
  • The conversion of the string into a Boolean , Float , or Integer can be suppressed by surrounding the string with single quotes. For example, the attribute value="'true'" is converted into the string "true"
• forcePluginActivation: A flag indicating whether the plug-in contributing the property tester should be loaded if necessary. As such, this flag should be used judiciously, in order to avoid unnecessary plug-in activations. Most clients should avoid setting this flag to true. This flag is only honored if the evaluation context used to evaluate this expression allows plug-in activation. Otherwise the flag is ignored and no plug-in loading takes place.

<!ELEMENT systemTest EMPTY>
<!ATTLIST systemTest
  property CDATA #REQUIRED
  value    CDATA #REQUIRED>

Tests a system property by calling the System.getProperty method and compares the result with the value specified through the value attribute.

• property: The name of an system property to test.
• value: The expected value of the property. The value is interpreted as a string value.

<!ELEMENT equals EMPTY>
<!ATTLIST equals
  value CDATA #REQUIRED>

This element is used to perform an equals check of the object in focus. The expression returns EvaluationResult.TRUE if the object is equal to the value provided by the attribute value. Otherwise EvaluationResult.FALSE is returned.

• value: The expected value. The value provided as a string is converted into a Java base type using the same rules as for the value attribute of the test expression.

<!ELEMENT count EMPTY>
<!ATTLIST count
  value CDATA #REQUIRED>

This element is used to test the number of elements in a collection.

• value: An expression to specify the number of elements in a list. Following wildcard characters can be used:
  • *: any number of elements
  • ?: no elements or one element
  • +: one or more elements
  • !: no elements
  • integer value: the list must contain the exact number of elements

<!ELEMENT with (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>
<!ATTLIST with
  variable CDATA #REQUIRED>

This element changes the object to be inspected for all its child element to the object referenced by the given variable. If the variable can not be resolved then the expression will throw an ExpressionException when evaluating it. The children of a with expression are combined using the and operator.

• variable: The name of the variable to be used for further inspection. It is up to the evaluator of an extension point to provide the variable in the variable pool.

<!ELEMENT resolve (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>
<!ATTLIST resolve
  variable CDATA #REQUIRED
  args     CDATA #IMPLIED>

This element changes the object to be inspected for all its child element to the object referenced by the given variable. If the variable can not be resolved then the expression will throw an ExpressionException when evaluating it. The children of a with expression are combined using the and operator.

• variable: The name of the variable to be resolved. This variable is then used as the object in focus for child element evaluation. It is up to the evaluator of an extension point to provide a corresponding variable resolver (see berry::IVariableResolver) through the evaluation context passed to the root expression element when evaluating the expression.
• args: Additional arguments passed to the variable resolver. Multiple arguments are seperated by commas. Each individual argument is converted into a Java base type using the same rules as defined for the value attribute of the test expression.

<!ELEMENT adapt (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>
<!ATTLIST adapt
  type CDATA #REQUIRED>

This element is used to adapt the object in focus to the type specified by the attribute type. The expression returns not loaded if either the adapter or the type referenced isn't loaded yet. It throws an ExpressionException during evaluation if the type name doesn't exist at all. The children of an adapt expression are combined using the and operator.

• type: the type to which the object in focus is to be adapted

<!ELEMENT iterate (not , and , or , instanceof , test , systemTest , equals , count , with , resolve , adapt , iterate , reference)*>
<!ATTLIST iterate
  operator (or|and)
  ifEmpty  (true | false) >

This element is used to iterate over a variable that is of type java.util.Collection. If the object in focus is not of type java.util.Collection then an ExpressionException will be thrown while evaluating the expression.

• operator: Either "and" or "or". The operator defines how the child elements will be combined. If not specified, "and" will be used.
• ifEmpty: The value return from the iterate expression if the collection is empty. If not specified then true is returned when the operator equals "and" and false is returned if the operator equals "or".

<!ELEMENT reference EMPTY>
<!ATTLIST reference
  definitionId CDATA #REQUIRED>

This element is used to reference an expression from the org.blueberry.core.expressions.definitions extension point. The expression definition will be evaluated within the current expression element using the current evaluation context.

• definitionId: the unique id of an expression from org.blueberry.core.expressions.definitions

Property Testers

Identifier

org.blueberry.core.expressions.propertyTesters

Description

This extension point allows to add properties to an already existing type. Those properties can then be used inside the expression language's test expression element.

Configuration Markup

<!ELEMENT extension (propertyTester*)>
<!ATTLIST extension
  point CDATA #REQUIRED
  id    CDATA #IMPLIED
  name  CDATA #IMPLIED>

• point: a fully qualified identifier of the target extension point
• id: an optional identifier of the extension instance
• name: an optional name of the extension instance

<!ELEMENT propertyTester EMPTY>
<!ATTLIST propertyTester
  id         CDATA #REQUIRED
  type       CDATA #REQUIRED
  namespace  CDATA #REQUIRED
  properties CDATA #REQUIRED
  class      CDATA #REQUIRED>

• id: Unique identifier for the property tester.
• type: The type to be extended by this property tester.
• namespace: A unique id determining the name space the properties are added to.
• properties: A comma separated list of properties provided by this property tester.
• class: The name of the class that implements the testing methods. The class must be public and extend org.blueberry.core.expressions.PropertyTester with a public 0-argument constructor.

Examples

<extension point="org.eclipse.core.expressions.propertyTesters">
  <propertyTester
    id="org.eclipse.jdt.ui.IResourceTester"
    type="org.eclipse.core.resources.IResource"
    namespace="org.eclipse.jdt.ui"
    properties="canDelete"
    class="org.eclipse.jdt.ui.internal.ResourceTester">
  </propertyTester>
</extension>