On 03/05/2024 10:08, Martin via Dwarf-discuss wrote:
Then next is the question, how to start an attempt to get it standardized?
I started on a DRAFT. (still discussing on the Pascal community, to
ensure it comprises everything required.
I post it here for comments on the general direction and format.
# Proposal to implement "properties" for Pascal
## Background
Pascal has a property construct, that allows a "variable like"
identifier, which can either point to a field (member variable) or a
getter/setter function.
They can be read/write, read only, write only.
TFoo = class
FField: integer;
function GetProp: integer;
procedure SetProp(AVal: Integer);
property MyProp: integer read GetProp write SetProp;
property MyOtherProp: integer read FField;
end;
Properties can exist in a structure, interface, or on a global level.
Properties can have one or more array like indexes.
TFoo = class
function GetProp(AIdx:word; AIdx2: boolean): integer;
procedure SetProp(AIdx:word; AIdx2: boolean; AVal: Integer);
property MyProp[AIdx:word; AIdx2: boolean]: integer read GetProp
write SetProp;
end;
Properties can share a method, and provide an index (constant) to
identify which property called the method.
TFoo = class
function GetProp(AIndex: Integer): integer;
procedure SetProp(AIndex: Integer; AValue: integer);
property MyProp1: integer index 1 read GetProp write SetProp;
property MyProp2: integer index 2 read GetProp write SetProp;
end;
Properties can be streamed and therefore can have a default value
(constant or via function). They can also have a "stored" value
(function) indicating if they need to be stored in the stream.
Properties can be elevated to a higher visibility (private/public) in
inherited classes.
There may be partial overlaps with properties in Objective-C and C#
## Proposed Changes
Introducing a new tag
DW_TAG_PROPERTY or DW_TAG_PROPERTY_PASCAL
This tag can occur anywhere where DW_TAG_MEMBER can occur. It can also
occur on a global scope.
It can have
DW_AT_NAME
DW_AT_TYPE
DW_AT_ACCESSIBILITY
DW_AT_decl_column, DW_AT_decl_file and DW_AT_decl_line.
It can then contain any of
DW_TAG_PROPERTY_SETTER
DW_TAG_PROPERTY_READER
DW_TAG_PROPERTY_DEFAULT
DW_TAG_PROPERTY_STORED
Each of them can have
DW_AT_PROPERTY_FORWARD reference/constant
refernce to the field or function
DW_AT_PROPERTY_OBJECT reference/expression/constant
the object on which the value is stored (value for
DW_OP_push_object_address)
can be omitted for inherited classes, if it computes to the same as
the current class
A getter (also "default" and "stored" should be a function returning the
same type as the property. It should either take no arguments or only
DW_AT_object_pointer
A setter should be a procedure, it should take optional
DW_AT_object_pointer and one argument of the same type as the property.
Instead of having attributes grouped in DW_TAG_PROPERTY_SETTER/... all
attribute could exist top level, in 4 versions. That would be shorter if
no object needs to be specified. But it is less flexible for later
additions.
For indexed properties the DW_TAG_PROPERTY also has
DW_TAG_PROPERTY_INDEX_LIST
containing one or more
DW_TAG_PROPERTY_INDEX
DW_AT_NAME
DW_AT_TYPE
DW_AT_VALUE reference or constant or expression (returning value)
DW_AT_IS_PROPERTY_VALUE flag
DW_AT_NAME and DW_AT_TYPE can be optional. They can be gotten from the
linked procedure
DW_AT_VALUE is optional. It is used when properties share a getter.
DW_AT_IS_PROPERTY_VALUE is optional. It can be used to specify the
position of the "assigned value" in a setter. If not specified the
assigned value will be passed as the last parametr.
To change visibility of an inherited property,
DW_TAG_PROPERTY
DW_AT_NAME
DW_AT_ACCESSIBILITY
OFF TOPIC:
For C# it may be of interest to allow DW_TAG_PROPERTY_SETTER/... to
have their own DW_AT_ACCESSIBILITY
For C# it may be of interest to allow an inlined function declaration
instead of DW_AT_PROPERTY_VALUE
## References
FreePascal property doc
https://www.freepascal.org/docs-html/ref/refse27.html
APPLE extension for Objective-C
https://github.com/llvm/llvm-project/blob/main/llvm/docs/SourceLevelDebugging.rst#debugging-information-format-1
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