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Object Shapes is used for accessing instance variables and representing the
"frozenness" of objects. Object instances have a "shape" and the shape
represents some attributes of the object (currently which instance variables are
set and the "frozenness"). Shapes form a tree data structure, and when a new
instance variable is set on an object, that object "transitions" to a new shape
in the shape tree. Each shape has an ID that is used for caching. The shape
structure is independent of class, so objects of different types can have the
same shape.
For example:
```ruby
class Foo
def initialize
# Starts with shape id 0
@a = 1 # transitions to shape id 1
@b = 1 # transitions to shape id 2
end
end
class Bar
def initialize
# Starts with shape id 0
@a = 1 # transitions to shape id 1
@b = 1 # transitions to shape id 2
end
end
foo = Foo.new # `foo` has shape id 2
bar = Bar.new # `bar` has shape id 2
```
Both `foo` and `bar` instances have the same shape because they both set
instance variables of the same name in the same order.
This technique can help to improve inline cache hits as well as generate more
efficient machine code in JIT compilers.
This commit also adds some methods for debugging shapes on objects. See
`RubyVM::Shape` for more details.
For more context on Object Shapes, see [Feature: #18776]
Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>
Co-Authored-By: Eileen M. Uchitelle <eileencodes@gmail.com>
Co-Authored-By: John Hawthorn <john@hawthorn.email>
29 lines
837 B
C
29 lines
837 B
C
#ifndef RUBY_TOPLEVEL_VARIABLE_H /*-*-C-*-vi:se ft=c:*/
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#define RUBY_TOPLEVEL_VARIABLE_H
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/**
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* @author Ruby developers <ruby-core@ruby-lang.org>
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* @copyright This file is a part of the programming language Ruby.
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* Permission is hereby granted, to either redistribute and/or
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* modify this file, provided that the conditions mentioned in the
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* file COPYING are met. Consult the file for details.
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*/
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/* per-object */
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struct gen_ivtbl {
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#if !SHAPE_IN_BASIC_FLAGS
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uint16_t shape_id;
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#endif
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uint32_t numiv;
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VALUE ivptr[FLEX_ARY_LEN];
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};
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int rb_ivar_generic_ivtbl_lookup(VALUE obj, struct gen_ivtbl **);
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#include "shape.h"
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#if !SHAPE_IN_BASIC_FLAGS
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shape_id_t rb_generic_shape_id(VALUE obj);
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#endif
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#endif /* RUBY_TOPLEVEL_VARIABLE_H */
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