Why use send when you can call the method directly?

Rails
1

I am reading through some code in active_record/relation/query_methods -
def
build_where (about line 230); and there are a couple of calls to send.
Here’s the first one
[@klass.send(:sanitize_sql, other.empty? ? opts : ([opts] + other))]

and here’s the second one
attributes = @klass.send(:expand_hash_conditions_for_aggregates, opts)

Why do we use send here when we could just call the method directly?
I mean, why is the first call not just
[@klass.sanitize_sql( other.empty? ? opts : ([opts] + other))]

Puzzled.

William

2

William F. wrote in post #977984:

I am reading through some code in active_record/relation/query_methods -
def
build_where (about line 230); and there are a couple of calls to send.
Here’s the first one
[@klass.send(:sanitize_sql, other.empty? ? opts : ([opts] + other))]

and here’s the second one
attributes = @klass.send(:expand_hash_conditions_for_aggregates, opts)

Why do we use send here when we could just call the method directly?
I mean, why is the first call not just
[@klass.sanitize_sql( other.empty? ? opts : ([opts] + other))]

Puzzled.

The only reason I could see to do this would be to get around an access
prohibition. You can use send in this way to call a private or
protected method.

William

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

3

Ah, thanks, yes that will probably be the reason.

4

On Thu, Jan 27, 2011 at 4:01 PM, William F.
[email protected]wrote:

Ah, thanks, yes that will probably be the reason.

Right… send comes in real handy in testing private methods, use it all
the
time

5

David K. wrote in post #978011:

On Thu, Jan 27, 2011 at 4:01 PM, William F.
[email protected]wrote:

Ah, thanks, yes that will probably be the reason.

Right… send comes in real handy in testing private methods, use it all
the
time

Then you’ve got bigger problems. You shouldn’t be testing your private
methods; that’s poking too deeply into an object’s implementation. You
should only ever test things that can be called from outside an object.

If a private method is an intermediate value in a computation, just test
the end result. If a private method really needs to be tested
separately, then it’s telling you that it wants to be public.

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

Sent from my iPhone

6

The @klass variable also could == some_object.class
If this is the case, then it could be a class method call, but still
don’t see the necessity to use #send.

Thanks, Ivan Povalyukhin

7

On Thu, Jan 27, 2011 at 8:39 PM, Marnen Laibow-Koser
[email protected]wrote:

Then you’ve got bigger problems. You shouldn’t be testing your private
methods; that’s poking too deeply into an object’s implementation. You
should only ever test things that can be called from outside an object.

If a private method is an intermediate value in a computation, just test
the end result. If a private method really needs to be tested
separately, then it’s telling you that it wants to be public.

I disagree – for me public is what I want to expose to outside access,
regardless of complexity or size, where the private logic may actually
be
the most complex, being called by a relatively light public function.
Now
this may be a difference between TDD and BDD in pure forms, but for me I
find if I drive my methods, public or private with test first, that the
end
resulting code is much more pliable. Also, if I have coverage on what
becomes complex private logic, at a more granular level – then I have a
much stronger project an also address minute issues closer to the
source. I
am sure you have your method of working that works for you, this is what
I
have found effective and successful.

8

David K. wrote in post #978200:

On Thu, Jan 27, 2011 at 8:39 PM, Marnen Laibow-Koser
[email protected]wrote:

Then you’ve got bigger problems. You shouldn’t be testing your private
methods; that’s poking too deeply into an object’s implementation. You
should only ever test things that can be called from outside an object.

If a private method is an intermediate value in a computation, just test
the end result. If a private method really needs to be tested
separately, then it’s telling you that it wants to be public.

I disagree – for me public is what I want to expose to outside access,

And therefore it is the only thing that is worth testing. No one cares
what your private logic is like, because they never see it.

regardless of complexity or size, where the private logic may actually
be
the most complex, being called by a relatively light public function.

Then test the return from the “light” public function, or make your
private logic public.

Now
this may be a difference between TDD and BDD in pure forms, but for me I
find if I drive my methods, public or private with test first, that the
end
resulting code is much more pliable.

No private method should have a test at all. That’s testing
implementation, and therefore is bad. You want to test interface only.

Also, if I have coverage on what
becomes complex private logic, at a more granular level – then I have a
much stronger project an also address minute issues closer to the
source.

No! All you have is brittle, implementation-dependent tests. What you
think is improving the quality of your code is actually hindering it.

I
am sure you have your method of working that works for you, this is what
I
have found effective and successful.

But it is neither. This is a matter of principles, not taste. Please
do not handwave away what I am telling you by saying that it is a matter
of taste – these are principles you need to understand. If you want to
disagree after you understand the principles, I will be interested to
hear your reasoning.

It is ineffective to test private methods because you never care about
the return value from a private method as such – if you cared about the
return value, you’d have made the method public.

It is unsuccessful to test private methods because you are tying your
tests too closely to implementation, which means they will fail if you
change your implementation – this despite the fact that one of the
points of testing is to tell you that your code still works when you
refactor your implementation.

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

9

Peter B. wrote in post #978204:
[…]

I would say that Marnen’s position is very consistent from what I see
from Kent Beck and others on the XP/TDD lists.

The XP crowd have been a major influence on my testing philosophy, even
though I’ve never done XP as such.

It took me a while to get
used to the approach, and I think it’s important to clarify that Marnen
isn’t saying not to test complex private methods.

Well, I guess I sort of am saying that, but only in the sense that you
probably shouldn’t have complex private methods that need their own
tests – that is, if your private methods are that complex, they should
be made public and/or decomposed.

He’s just saying that
if they are complex, maybe you’ve discovered another composed object’s
public method.

Or the same object’s public method, or a method that is too long…

SRP and all that . . .

I suppose. Basically, I think if you have a private method that is
complex enough that wants to be tested in isolation, then that is a
symptom of an underlying design problem: your methods are insufficiently
accessible, or insufficiently atomic, or your code is otherwise
insufficiently modular (say, by virtue of needing a new class
introduced). Fix the underlying problem and the need for
“so-big-it-needs-its-own-tests” private methods will go away.

Best Wishes,
Peter

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

10

On Jan 28, 2011, at 11:55 AM, David K. wrote:

If a private method is an intermediate value in a computation, just test
the end result. If a private method really needs to be tested
separately, then it’s telling you that it wants to be public.

I disagree – for me public is what I want to expose to outside access,
regardless of complexity or size, where the private logic may actually be the most
complex, being called by a relatively light public function. Now this may be a
difference between TDD and BDD in pure forms, but for me I find if I drive my
methods, public or private with test first, that the end resulting code is much
more pliable. Also, if I have coverage on what becomes complex private logic, at a
more granular level – then I have a much stronger project an also address minute
issues closer to the source. I am sure you have your method of working that works
for you, this is what I have found effective and successful.

I would say that Marnen’s position is very consistent from what I see
from Kent Beck and others on the XP/TDD lists. It took me a while to get
used to the approach, and I think it’s important to clarify that Marnen
isn’t saying not to test complex private methods. He’s just saying that
if they are complex, maybe you’ve discovered another composed object’s
public method. SRP and all that . . .

Best Wishes,
Peter