[RRR] Robert's Ruby Riddle: Local or Method

[Robert Dober]

Hi list I was just thinking it might fun to present some of Ruby's
features in form of a riddle.
There was an interesting thread yesterday and as I always forget the
basics I wrote some testcode to find out if the local or the method
prevails, I made a stupid
error and had to rewrite the code, or maybe did I not? This depends on
the answer of the riddle.
Todays Ruby Riddle is:

Can the following code be used to test if the argument of puts is the
local variable "a" or the method "a"? And if so please explain how.

<code>
a = 42
def a; 42 end
puts a
</code>
I leave some blank lines here so that people can reply without
spoiling if for other readers.

 

[John Joyce]

Hi list I was just thinking it might fun to present some of Ruby's
features in form of a riddle.
There was an interesting thread yesterday and as I always forget the
basics I wrote some testcode to find out if the local or the method
prevails, I made a stupid
error and had to rewrite the code, or maybe did I not? This depends on
the answer of the riddle.
Todays Ruby Riddle is:

Can the following code be used to test if the argument of puts is the
local variable "a" or the method "a"? And if so please explain how.

<code>
a = 42
def a; 42 end
puts a
</code>
I leave some blank lines here so that people can reply without
spoiling if for other readers.

very simple
puts a
will out put the object a
in the scope you def'd the 'a' method
it belongs to either Object or IRB
to get the method's output you need to do
self.a

 

[Morton Goldberg]

Can the following code be used to test if the argument of puts is the
local variable "a" or the method "a"? And if so please explain how.

<code>
a = 42
def a; 42 end
puts a
</code>

I can't see how it can as it is written above, but with a little
modification ...

<code>
a = 42
def a; 43 end
puts a
puts a()
</code>

This makes it clear that Ruby prefers the local variable when it's
defined. It also makes it clear that one doesn't have to write self.a
to get the method called.

<code>
# a = 42
def a; 43 end
puts a
puts a()
</code>

And this makes it clear that Ruby will call the method when the local
is not defined.

Regards, Morton

 

[Robert Dober]

I can't see how it can as it is written above, but with a little
modification ...

<code>
a = 42
def a; 43 end
puts a
puts a()
</code>

This makes it clear that Ruby prefers the local variable when it's
defined. It also makes it clear that one doesn't have to write self.a
to get the method called.

<code>
# a = 42
def a; 43 end
puts a
puts a()
</code>

And this makes it clear that Ruby will call the method when the local
is not defined.

Regards, Morton

No Morton, there is a perfect solution with the code snippet I
posted... it is simple, I will tell you later
R.

 

[Morton Goldberg]

No Morton, there is a perfect solution with the code snippet I
posted... it is simple, I will tell you later

Really? Just by running the code as you posted it and looking at the
output? I'll be impressed and surely learn something if that's the
case. I look forward to your explanation.

Regards, Morton

 

[Martin DeMello]

Can the following code be used to test if the argument of puts is the
local variable "a" or the method "a"? And if so please explain how.

<code>
a = 42
def a; 42 end
puts a
</code>
I leave some blank lines here so that people can reply without
spoiling if for other readers.

Here be spoiler:

martin@dabba ~ $ cat puzzle.rb
a = 42
def a; 42 end
puts a

martin@dabba ~ $ ruby -r profile puzzle.rb 2>&1 | grep "Object#a"

martin@dabba ~ $ tail -2 puzzle.rb > puzzle1.rb

martin@dabba ~ $ cat puzzle1.rb
def a; 42 end
puts a

martin@dabba ~ $ ruby -r profile puzzle1.rb 2>&1 | grep "Object#a"
0.00 0.13 0.00 1 0.00 0.00 Object#a

martin

 

[Robert Dober]

Here be spoiler:


martin@dabba ~ $ cat puzzle.rb
a = 42
def a; 42 end
puts a

martin@dabba ~ $ ruby -r profile puzzle.rb 2>&1 | grep "Object#a"

martin@dabba ~ $ tail -2 puzzle.rb > puzzle1.rb

martin@dabba ~ $ cat puzzle1.rb
def a; 42 end
puts a

martin@dabba ~ $ ruby -r profile puzzle1.rb 2>&1 | grep "Object#a"
0.00 0.13 0.00 1 0.00 0.00 Object#a

martin

Bravo Martin, this is my preferred solution, another one would be the
debugger, but that is not worth the effort.
Too bad there are no prices, I just wanted to feature the profiler...

Cheers
Robert

 

[Morton Goldberg]

Bravo Martin, this is my preferred solution, another one would be the
debugger, but that is not worth the effort.
Too bad there are no prices, I just wanted to feature the profiler...

I admit using the profiler is clever, but a bit of an anticlimax. I
was hoping for something far more exciting and mysterious. However,
since I can Ruby right out of my text editor, I still think the code
variation scheme I proposed is the easier, more practical way to
decide the question.

Regards, Morton

 

[James Gray]

Hi list I was just thinking it might fun to present some of Ruby's
features in form of a riddle.
There was an interesting thread yesterday and as I always forget the
basics I wrote some testcode to find out if the local or the method
prevails, I made a stupid
error and had to rewrite the code, or maybe did I not? This depends on
the answer of the riddle.
Todays Ruby Riddle is:

Can the following code be used to test if the argument of puts is the
local variable "a" or the method "a"? And if so please explain how.

<code>
a = 42
def a; 42 end
puts a
</code>
I leave some blank lines here so that people can reply without
spoiling if for other readers.

You can set a trace function for this:

$ ruby -e 'set_trace_func lambda { |event, _, _, name, _, _| puts
"method called" if event == "call" and name == :a }; eval(ARGF.read)'
riddle.rb
42
$ ruby -e 'set_trace_func lambda { |event, _, _, name, _, _| puts
"method called" if event == "call" and name == :a };
eval(ARGF.read.to_a[1..-1].join)' riddle.rb
method called
42

James Edward Gray II

 

[Robert Dober]

Hi list I was just thinking it might fun to present some of Ruby's
features in form of a riddle.
There was an interesting thread yesterday and as I always forget the
basics I wrote some testcode to find out if the local or the method
prevails, I made a stupid
error and had to rewrite the code, or maybe did I not? This depends on
the answer of the riddle.
Todays Ruby Riddle is:

Can the following code be used to test if the argument of puts is the
local variable "a" or the method "a"? And if so please explain how.

<code>
a = 42
def a; 42 end
puts a
</code>
I leave some blank lines here so that people can reply without
spoiling if for other readers.

You can set a trace function for this:

$ ruby -e 'set_trace_func lambda { |event, _, _, name, _, _| puts
"method called" if event == "call" and name == :a }; eval(ARGF.read)'
riddle.rb
42
$ ruby -e 'set_trace_func lambda { |event, _, _, name, _, _| puts
"method called" if event == "call" and name == :a };
eval(ARGF.read.to_a[1..-1].join)' riddle.rb
method called
42

James Edward Gray II

I thought the debugger and the profiler were the only solutions, that
is quite one James!
R.