where to find Native Ruby source code such as instance_exec? - ruby

Question

i know that there is the function "method(:instance_exec).source_location" to look for source code, but only works for code in gems. But it returns null in this particular case since the method is from native ruby. i am googling but i am not able to find where this is written.
in my particular case, i want to have a better idea of how instance_exec changes the values of the scope of a proc
going on a tangent, im looking to do this for college
precondition { divisor != 0 }
postcondition { |result| result * divisor == dividend}
def divide(dividend, divisor)
dividend / divisor
end
i know instance_exec changes 'self' value in the proc scope. i want to add 'divisor' to the scope of { divisor != 0 } proc when i run it, and i think that reading the implementation of instance_exec would be very helpfull.
Since it is for college, i cant use any gem to do this, only standard ruby
PS right_click + Go To + Implementation only shows me
def instance_exec(*args)
# This is a stub implementation, used for type inference (actual method behavior may differ)
yield
end

Answer 1

i know that there is the function "method(:instance_exec).source_location" to look for source code, but only works for code in gems.
That's not true. Method#source_location works just fine for methods which are not in gems:
module Foo
def bar; end
end
p Foo.instance_method(:bar).source_location
#=> ['test.rb', 2]
There is no gem here. In fact, it even works if I don't use any file at all, just by using ruby -e on the command line; the result will be ['-e', 2] in that case.
On the other hand, if there is no Ruby source, then it will return nil even for gems.
The return value of Method#source_location has nothing to do with whether or not the method is from a gem, the only thing that matters is whether there even is a Ruby source to locate.
But it returns null in this particular case since the method is from native ruby.
It shouldn't return null, it should return either a two-element array or nil, but never null. There seems to be something seriously broken with your Ruby installation if that is really the case.
i am googling but i am not able to find where this is written.
It will be somewhere in the source code of the Ruby implementation you are using. You haven't specified which implementation you are using, so I cannot tell you exactly, but here are some examples:
In Rubinius, it is implemented in core/basic_object.rb:
def instance_exec(*args, &prc)
raise ::LocalJumpError, "Missing block" unless block_given?
env = prc.block
return prc.ruby_method.call(*args) if prc.ruby_method
lexical_scope = env.lexical_scope
if ::ImmediateValue === self
lexical_scope = lexical_scope.using_disabled_scope
else
sc = ::Rubinius::Type.object_singleton_class(self)
lexical_scope = lexical_scope.using_current_as(sc)
end
return env.call_under(self, lexical_scope, true, *args)
end
In TruffleRuby, it is implemented in src/main/java/org/truffleruby/core/basicobject/BasicObjectNodes.java:
#CoreMethod(names = "instance_exec", needsBlock = true, rest = true)
public abstract static class InstanceExecNode extends CoreMethodArrayArgumentsNode {
public static InstanceExecNode create() {
return InstanceExecNodeFactory.create(null);
}
#Child private CallBlockNode callBlockNode = CallBlockNode.create();
abstract Object executeInstanceExec(Object self, Object[] args, RubyProc block);
#Specialization
protected Object instanceExec(Object receiver, Object[] arguments, RubyProc block) {
final DeclarationContext declarationContext = new DeclarationContext(
Visibility.PUBLIC,
new SingletonClassOfSelfDefaultDefinee(receiver),
block.declarationContext.getRefinements());
return callBlockNode
.executeCallBlock(declarationContext, block, receiver, block.block, arguments);
}
#Specialization
protected Object instanceExec(Object receiver, Object[] arguments, NotProvided block) {
throw new RaiseException(getContext(), coreExceptions().localJumpError("no block given", this));
}
}