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Difference between revisions of "OT Bytecode Attributes/OTSpecialAccess"

(New page: =Attribute OTSpecialAccess= ===Intent=== This attribute combines information about several situations where accessing one element across classes requires special treatment: * '''decapsula...)
 
Line 3: Line 3:
 
===Intent===
 
===Intent===
 
This attribute combines information about several situations where accessing one element across classes requires special treatment:
 
This attribute combines information about several situations where accessing one element across classes requires special treatment:
−
* '''decapsulation''' (base method accessed by role)              => OTRE removes protection
+
* '''method-decapsulation''' (inaccessible base method accessed by role)              => OTRE provides accessor method
−
* '''callout-to-field''' (base field accessed by role)            => OTRE adds setter/getter
+
* '''field-decapsulation''' (inaccessible base field accessed by role)            => OTRE adds setter/getter
 +
* '''super-method-access''' (a base method is accessed using a '''base.super''' call) => OTRE provides accessor method
 
* '''base-class access''' -- two situations
 
* '''base-class access''' -- two situations
 +
:*    all base classes that are affected by method- or field-decapsulation
 
:*    base-class decapsulation (role accesses invisible base-class) => OTRE removes protection
 
:*    base-class decapsulation (role accesses invisible base-class) => OTRE removes protection
−
:*    super-base-class access (team adapts a super of a declared base-class)
 
  
 
===Location:===
 
===Location:===
−
TODO
+
Team class containing one or more roles requesting decapsulation.
  
 
===Content:===
 
===Content:===
−
TODO
+
Two consecutive lists:
 +
* a polymorphic list of decapsulation info for members (methods, fields, super-methods)
 +
* a list of base classes (some of this may be subject to decapsulation)
  
 
===Purpose:===
 
===Purpose:===
−
TODO
+
The OTRE uses this attribute to make accessible those elements that shall be
 +
accessed using decapsulation. This is done by generating access methods for all
 +
affected methods, fields and super-methods.
 +
Base class decapsulation is supported by changing the access flags of the base class.
  
 
===Format:===
 
===Format:===
−
<pre>   TODO</pre>
+
   OTSpecialAccess {
 +
        u2 attribute_name_index;
 +
        u4 attribute_length;
 +
        u2 member_decapsulation_count;
 +
        MemberDecapsulation member_decapsulations[member_decapsulation_count];
 +
        u2 baseclass_count;
 +
        Baseclass baseclasses[baseclass_count];
 +
  }
 +
  union MemberDecapsulation {
 +
        MethodDecapsulation methodDesc;
 +
        FieldDecapsulation fieldDesc;
 +
        SuperMethodAccess superMethodDesc;
 +
  }
 +
  MethodDecapsulation {
 +
        u1 selector=1;
 +
        u2 class_name_index;
 +
        u2 encoded_method_selector_index;
 +
        u2 signature_index;
 +
  }
 +
  FieldDecapsulation {
 +
        u1 selector=2;
 +
        u1 flags;
 +
        u2 class_name_index;
 +
        u2 field_name_index;
 +
        u2 field_signature_index;
 +
  }
 +
  SuperMethodAccess {
 +
        u1 selector=3;
 +
        u2 class_name_index;
 +
        u2 superclass_name_index;
 +
        u2 method_selector_index;
 +
        u2 signature_index;
 +
  }
 +
  Baseclass {
 +
        u2 baseclass_name_index;
 +
        u1 is_decapsulation;
 +
  }
  
−
The items of the OTSpecialAccess structure are as follows:  
+
The items of the '''OTSpecialAccess''' structure are as follows:  
 
*attribute_name_index
 
*attribute_name_index
−
:The constant_pool entry at that index must be a CONSTANT_Utf8_info representing the string "CallinRoleBaseBindings".  
+
:The constant_pool entry at that index must be a CONSTANT_Utf8_info representing the string "OTSpecialAccess".  
 
*attribute_length
 
*attribute_length
 
:The value of the attribute_length item indicates the length of the attribute, excluding the initial six bytes.  
 
:The value of the attribute_length item indicates the length of the attribute, excluding the initial six bytes.  
−
*TODO
+
*member_decapsulation_count
 +
:Number of MemberDecapsulation entries
 +
*member_decapsulations
 +
:Array of entries describing decapsulation of one member. Each element is one of '''MethodDecapsulation''', '''FieldDecapsulation''' or '''SuperMethodAccess'''.
 +
*baseclass_count
 +
:Number of entries for baseclasses
 +
*baseclasses
 +
:Array of base classes to which the current team binds roles.
 +
 
 +
The items of the '''MethodDecapsulation''' structure are as follows:
 +
*selector
 +
:Constant 1 to discriminate among alternatives of MemberDecapsulation
 +
*class_name_index
 +
:Constant pool index pointing to the name of the bound base class
 +
*encoded_method_selector_index
 +
:Constant pool index pointing to the name of the decapsulated method. For non-constructor methods this name is encoded either as <tt>declaringClass!selector</tt> (for static methods) or <tt>declaringClass?selector</tt> (for instance methods). Here <tt>declaringClass</tt> is the class actually declaring the method
 +
* signature_index
 +
:Constant pool index for the string-encoded signature of the method
 +
 
 +
The items of the '''FieldDecapsulation''' structure are as follows:
 +
*selector
 +
:Constant 2 to discriminate among alternatives of MemberDecapsulation
 +
*class_name_index
 +
:Constant pool index pointing to the name of the bound base class
 +
*field_name_index
 +
:Constant pool index pointing to the name of the decapsulated field.
 +
* signature_index
 +
:Constant pool index for the string-encoded signature (type) of the field
 +
 
 +
The items of the '''SuperMethodAccess''' structure are as follows:
 +
*selector
 +
:Constant 3 to discriminate among alternatives of MemberDecapsulation
 +
*class_name_index
 +
:Constant pool index pointing to the name of the declaring class for the method
 +
*superclass_name_index
 +
:Constant pool index pointing to the name of the superclass of the declaring class for the method
 +
*method_selector_index
 +
:Constant pool index pointing to the selector of the decapsulated method.
 +
* signature_index
 +
:Constant pool index for the string-encoded signature of the method
 +
 
 +
The items of the '''Baseclass''' structure are as follows:
 +
*baseclass_name_index
 +
:Constant pool index for the name of a bound baseclass
 +
*is_decapsulation
 +
:flag (0=false, 1=true) to signal whether decapsulation is applied to the baseclass itself
 +
 
  
 
[[Category:Object Teams Development]]
 
[[Category:Object Teams Development]]

Revision as of 13:38, 3 July 2010

Attribute OTSpecialAccess

Intent

This attribute combines information about several situations where accessing one element across classes requires special treatment:

  • method-decapsulation (inaccessible base method accessed by role) => OTRE provides accessor method
  • field-decapsulation (inaccessible base field accessed by role) => OTRE adds setter/getter
  • super-method-access (a base method is accessed using a base.super call) => OTRE provides accessor method
  • base-class access -- two situations
  • all base classes that are affected by method- or field-decapsulation
  • base-class decapsulation (role accesses invisible base-class) => OTRE removes protection

Location:

Team class containing one or more roles requesting decapsulation.

Content:

Two consecutive lists:

  • a polymorphic list of decapsulation info for members (methods, fields, super-methods)
  • a list of base classes (some of this may be subject to decapsulation)

Purpose:

The OTRE uses this attribute to make accessible those elements that shall be accessed using decapsulation. This is done by generating access methods for all affected methods, fields and super-methods. Base class decapsulation is supported by changing the access flags of the base class.

Format:

 OTSpecialAccess {
       u2 attribute_name_index;
       u4 attribute_length;
       u2 member_decapsulation_count;
       MemberDecapsulation member_decapsulations[member_decapsulation_count];
       u2 baseclass_count;
       Baseclass baseclasses[baseclass_count];
 }
 union MemberDecapsulation {
       MethodDecapsulation methodDesc;
       FieldDecapsulation fieldDesc;
       SuperMethodAccess superMethodDesc;
 }
 MethodDecapsulation {
       u1 selector=1;
       u2 class_name_index;
       u2 encoded_method_selector_index;
       u2 signature_index;
 }
 FieldDecapsulation {
       u1 selector=2;
       u1 flags;
       u2 class_name_index;
       u2 field_name_index;
       u2 field_signature_index;
 }
 SuperMethodAccess {
       u1 selector=3;
       u2 class_name_index;
       u2 superclass_name_index;
       u2 method_selector_index;
       u2 signature_index;
 }
 Baseclass {
       u2 baseclass_name_index;
       u1 is_decapsulation;
 }

The items of the OTSpecialAccess structure are as follows:

  • attribute_name_index
The constant_pool entry at that index must be a CONSTANT_Utf8_info representing the string "OTSpecialAccess".
  • attribute_length
The value of the attribute_length item indicates the length of the attribute, excluding the initial six bytes.
  • member_decapsulation_count
Number of MemberDecapsulation entries
  • member_decapsulations
Array of entries describing decapsulation of one member. Each element is one of MethodDecapsulation, FieldDecapsulation or SuperMethodAccess.
  • baseclass_count
Number of entries for baseclasses
  • baseclasses
Array of base classes to which the current team binds roles.

The items of the MethodDecapsulation structure are as follows:

  • selector
Constant 1 to discriminate among alternatives of MemberDecapsulation
  • class_name_index
Constant pool index pointing to the name of the bound base class
  • encoded_method_selector_index
Constant pool index pointing to the name of the decapsulated method. For non-constructor methods this name is encoded either as declaringClass!selector (for static methods) or declaringClass?selector (for instance methods). Here declaringClass is the class actually declaring the method
  • signature_index
Constant pool index for the string-encoded signature of the method

The items of the FieldDecapsulation structure are as follows:

  • selector
Constant 2 to discriminate among alternatives of MemberDecapsulation
  • class_name_index
Constant pool index pointing to the name of the bound base class
  • field_name_index
Constant pool index pointing to the name of the decapsulated field.
  • signature_index
Constant pool index for the string-encoded signature (type) of the field

The items of the SuperMethodAccess structure are as follows:

  • selector
Constant 3 to discriminate among alternatives of MemberDecapsulation
  • class_name_index
Constant pool index pointing to the name of the declaring class for the method
  • superclass_name_index
Constant pool index pointing to the name of the superclass of the declaring class for the method
  • method_selector_index
Constant pool index pointing to the selector of the decapsulated method.
  • signature_index
Constant pool index for the string-encoded signature of the method

The items of the Baseclass structure are as follows:

  • baseclass_name_index
Constant pool index for the name of a bound baseclass
  • is_decapsulation
flag (0=false, 1=true) to signal whether decapsulation is applied to the baseclass itself
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