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Document rb_equal() and clarify the relation with Kernel#===

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* Multiple times people have been confused and believed rb_equal()
  called #=== but it does not, it calls #==.
* This optimization has a subtle side effect for Float::NAN,
  which is now documented.
This commit is contained in:
Benoit Daloze 2020-05-06 00:11:42 +02:00
parent 00a9d697a8
commit 48d509cefc
1 changed files with 19 additions and 4 deletions
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23
object.c
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@ -141,7 +141,22 @@ rb_obj_setup(VALUE obj, VALUE klass, VALUE type)
* Same as \c Object#===, case equality.
*++
*/
static VALUE
case_equal(VALUE obj1, VALUE obj2) {
/* The default implementation of #=== is
* to call #== with the rb_equal() optimization. */
return rb_equal(obj1, obj2);
}
/*!
* This function is an optimized version of calling #==.
* It checks equality between two objects by first doing a fast
* identity check using using C's == (same as BasicObject#equal?).
* If that check fails, it calls #== dynamically.
* This optimization actually affects semantics,
* as Float::NAN == Float::NAN is false,
* but rb_equal(Float::NAN, Float::NAN) is true!
*/
VALUE
rb_equal(VALUE obj1, VALUE obj2)
{
@ -4598,7 +4613,7 @@ InitVM_Object(void)
rb_define_private_method(rb_cModule, "method_undefined", rb_obj_dummy1, 1);
rb_define_method(rb_mKernel, "nil?", rb_false, 0);
rb_define_method(rb_mKernel, "===", rb_equal, 1);
rb_define_method(rb_mKernel, "===", case_equal, 1);
rb_define_method(rb_mKernel, "=~", rb_obj_match, 1);
rb_define_method(rb_mKernel, "!~", rb_obj_not_match, 1);
rb_define_method(rb_mKernel, "eql?", rb_obj_equal, 1);
@ -4665,7 +4680,7 @@ InitVM_Object(void)
rb_define_method(rb_cNilClass, "&", false_and, 1);
rb_define_method(rb_cNilClass, "|", false_or, 1);
rb_define_method(rb_cNilClass, "^", false_xor, 1);
rb_define_method(rb_cNilClass, "===", rb_equal, 1);
rb_define_method(rb_cNilClass, "===", case_equal, 1);
rb_define_method(rb_cNilClass, "nil?", rb_true, 0);
rb_undef_alloc_func(rb_cNilClass);
@ -4751,7 +4766,7 @@ InitVM_Object(void)
rb_define_method(rb_cTrueClass, "&", true_and, 1);
rb_define_method(rb_cTrueClass, "|", true_or, 1);
rb_define_method(rb_cTrueClass, "^", true_xor, 1);
rb_define_method(rb_cTrueClass, "===", rb_equal, 1);
rb_define_method(rb_cTrueClass, "===", case_equal, 1);
rb_undef_alloc_func(rb_cTrueClass);
rb_undef_method(CLASS_OF(rb_cTrueClass), "new");
@ -4763,7 +4778,7 @@ InitVM_Object(void)
rb_define_method(rb_cFalseClass, "&", false_and, 1);
rb_define_method(rb_cFalseClass, "|", false_or, 1);
rb_define_method(rb_cFalseClass, "^", false_xor, 1);
rb_define_method(rb_cFalseClass, "===", rb_equal, 1);
rb_define_method(rb_cFalseClass, "===", case_equal, 1);
rb_undef_alloc_func(rb_cFalseClass);
rb_undef_method(CLASS_OF(rb_cFalseClass), "new");
}