get caller of method

T

thomas coopman

Hi,

Does there exist a method to get the object or type of object that calls this method?

for example:

class Foo
do
end
class Bar
do
end

do
if caller.kind_of?(Foo)
puts "Foo"
elsif caller.kind_of?(Bar)
puts "Bar"
end
end

Thanks!
 
A

Ashley Moran

Hi,

Does there exist a method to get the object or type of object that
calls this method?

for example:

class Foo
do
end
class Bar
do
end

do
if caller.kind_of?(Foo)
puts "Foo"
elsif caller.kind_of?(Bar)
puts "Bar"
end
end

Thanks!
Click to expand...

Thomas

I'm assuming you meant something like:

class Foo
def do_stuff
do_something
end
end
class Bar
def do_stuff
do_something
end
end

def do_something
if caller.kind_of?(Foo)
puts "Foo"
elsif caller.kind_of?(Bar)
puts "Bar"
end
end

since "do" is a reserved word in Ruby.

In this case you can do the following:

def do_something(b = binding)
case eval("self", b)
when Foo then "Called by Foo"
when Bar then "Bar told me to do it"
end
end

Then you get:
Foo.new.do_stuff
=> "Called by Foo"

Bar.new.do_stuff
=> "Bar told me to do it"

Note however that it would be possible for a method to "lie" and pass
in another binding when the method is called. And also it won't work
in this case:

class Foo
do_something
end

because the calling object is an instance of Class, but you could use:

def do_something(b = binding)
case eval("self.name", b)
when "Foo" then "Called when building Foo"
when "Bar" then "Bar's creator told me to do it"
end
end

and you get:
class Foo
do_something
end
=> "Called when building Foo"


Maybe there is a better way to do this but it's a starter for 10.


Ashley
 
M

Morton Goldberg

Although others may suggest fancier techniques, I suggest a very
simple approach -- just have the caller identify itself. For example:

#! /usr/bin/ruby -w

class Foo

def connect
@server = Server.new
@server.connect(self)
end

end

class Bar < Foo
end

class Server

def connect(sender)
@client = sender
puts @client.class.name
end

end

Foo.new.connect
Bar.new.connect

# --- end of code ----

Regards, Morton
 
E

Erik Veenstra

I didn't know about this b=binding trick.
Quiet interesting... ;]

Thanks,

gegroet,
Erik V.
 
S

Sean O'Halpin

Thomas

I'm assuming you meant something like:

class Foo
def do_stuff
do_something
end
end
class Bar
def do_stuff
do_something
end
end

def do_something
if caller.kind_of?(Foo)
puts "Foo"
elsif caller.kind_of?(Bar)
puts "Bar"
end
end

since "do" is a reserved word in Ruby.

In this case you can do the following:

def do_something(b = binding)
case eval("self", b)
when Foo then "Called by Foo"
when Bar then "Bar told me to do it"
end
end

Then you get:
Foo.new.do_stuff
=> "Called by Foo"

Bar.new.do_stuff
=> "Bar told me to do it"

Note however that it would be possible for a method to "lie" and pass
in another binding when the method is called. And also it won't work
in this case:

class Foo
do_something
end

because the calling object is an instance of Class, but you could use:

def do_something(b = binding)
case eval("self.name", b)
when "Foo" then "Called when building Foo"
when "Bar" then "Bar's creator told me to do it"
end
end

and you get:
class Foo
do_something
end
=> "Called when building Foo"


Maybe there is a better way to do this but it's a starter for 10.


Ashley
Click to expand...
Hi,

It's not clear to me what you're doing with the binding. You don't
need it for your example and it won't work the way you seem to think.

The example below shows you don't need to do anything fancy to get hold of self:

def do_something
case self
when Foo
puts "Called by Foo"
when Bar
puts "Bar told me to do it"
when Class
case self.name
when "Foo"
puts "Class Foo did it"
end
end
end

class Foo
def do_stuff
do_something
end
end
class Bar
def do_stuff
do_something
end
end

Foo.new.do_stuff
Bar.new.do_stuff
class Foo
do_something
end
__END__
Called by Foo
Bar told me to do it
Class Foo did it

The next example shows that the binding you create in the argument
list is local to the method definition, not to the caller (which I
think is what you're thinking).

def test_binding(str, b = binding)
x = 2
p eval(str, b)
end

class Foo
x = 1
test_binding "x", binding
test_binding "x"
end
__END__
1
2

Please feel free to correct me if I've gotten hold of the wrong end of
the stick (it has been known ;)

Regards,
Sean
 
T

transfire

thomas said:
Hi,

Does there exist a method to get the object or type of object that calls this method?
Click to expand...

The same question was asked just a few days ago. It's generally a good
rule of thumb to do a search first before asking --just FYI.

Anyhow, the #binding turns the current context/closure into an object
that you can pass around an reuse. You can evaluate any code against a
binding via:

Kernel.eval( "code here", aBinding)

If you pass a block, btw, you can't get it's binding and via it the
caller.

T.
 
A

Ashley Moran

Hi,

It's not clear to me what you're doing with the binding. You don't
need it for your example and it won't work the way you seem to think.

The example below shows you don't need to do anything fancy to get hold of
self:
Click to expand...

Please feel free to correct me if I've gotten hold of the wrong end of
the stick (it has been known ;)

Regards,
Sean
Click to expand...


Hi Sean

Seems I misunderstood the scope of "self". I assumed that since a Food
instance was calling a method in another object (the application instance of
Object) that self would be the global "main" object. IE:

irb(main):003:0> class Foo
irb(main):004:1> def test
irb(main):005:2> global_test
irb(main):006:2> end
irb(main):007:1> end
=> nil
irb(main):008:0> def global_test
irb(main):009:1> puts self.class
irb(main):010:1> puts self.inspect
irb(main):011:1> end
=> nil
irb(main):012:0> Foo.new.test

I expected:
Object
main

But you actually get:
Foo
#<Foo:0x8143b18>


I have to say, I don't understand this behaviour. Maybe I am missing
something. I assume it is to do with class nesting?

Ashley
 
S

Sean O'Halpin

< SNIP bit that shows me up as clueless :) >
Click to expand...

Don't take it so hard - we're all still learning :)
Hi Sean

Seems I misunderstood the scope of "self". I assumed that since a Food
instance was calling a method in another object (the application instance of
Object) that self would be the global "main" object. IE:

irb(main):003:0> class Foo
irb(main):004:1> def test
irb(main):005:2> global_test
irb(main):006:2> end
irb(main):007:1> end
=> nil
irb(main):008:0> def global_test
irb(main):009:1> puts self.class
irb(main):010:1> puts self.inspect
irb(main):011:1> end
=> nil
irb(main):012:0> Foo.new.test

I expected:
Object
main

But you actually get:
Foo
#<Foo:0x8143b18>


I have to say, I don't understand this behaviour. Maybe I am missing
something. I assume it is to do with class nesting?

Ashley
Click to expand...
self is dynamically scoped to always return the current receiver.

It is not lexically scoped, i.e. it does not depend on ~where~ the
definition is but on how it is called.

Look at this example:

@name = "I'm main"
def name
@name
end

def m1
p [self, name]
@name = name.reverse
end

m1 # called in scope of self == main

class Foo
attr_accessor :name
def initialize(name)
@name = name
end
def name
@name
end
def m2
m1 # called in scope of self == instance of Foo
end
end

f = Foo.new("I'm foo")
f.m2
f.m2
__END__
[#<Object:0x27f91f8 @name="I'm main">, "I'm main"]
[#<Foo:0x2867598 @name="I'm foo">, "I'm foo"]
[#<Foo:0x2867598 @name="oof m'I">, "oof m'I"]

HTH

Regards,
Sean
 
P

Pit Capitain

Sean said:
Don't take it so hard - we're all still learning :)
Click to expand...

And some actually enjoy it :)

Ashley, in addition to Sean's answer, remember that the methods you
define at the toplevel, outside of any class, aren't singleton methods
of the "main" object. Instead, they are private methods of class Object.
Since every class is a subclass of Object, they inherit these "toplevel"
methods. In your method Foo#test, you're actually calling

self.global_test

so you're not calling a method of a different object. The following is
based on your code above:

f = Foo.new

f.test
# => #<Foo:0x2b84b80>

f.global_test rescue puts $!
# => private method `global_test' called for #<Foo:0x2b84b80>

You see from the error message, that global_test is a private method,
and I'm calling it for my Foo instance. Now I'm going to make the method
public:

class Object
public :global_test
end

f.global_test
# => #<Foo:0x2b84b80>

Regards,
Pit
 
A

Ashley Moran

Thanks for the replies people


Ashley, in addition to Sean's answer, remember that the methods you
define at the toplevel, outside of any class, aren't singleton methods
of the "main" object. Instead, they are private methods of class Object.
Since every class is a subclass of Object, they inherit these "toplevel"
methods. In your method Foo#test, you're actually calling

=A0 =A0self.global_test

so you're not calling a method of a different object. The following is
based on your code above:
Click to expand...


I think I get it now. I assumed that top-level methods were singleton=20
methods. I'll have to watch this - I've been busy writing DSLs lately so m=
y=20
code is apparently littered with methods added to Object, I didn't realise=
=20
they could be called anywhere.

Ashley

=2D-=20
"If you do it the stupid way, you will have to do it again"
- Gregory Chudnovsky
 

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