From: Robert Klemme <shortcutter@...>
Date: 2013-03-30T07:16:14+09:00
Subject: Re: Ruby Typing?

--047d7b6da1d26c844b04d9179ef9
Content-Type: text/plain; charset=ISO-8859-1

On Fri, Mar 29, 2013 at 5:06 PM, John n/a <lists@ruby-forum.com> wrote:

> Hi everyone. I'm very new to ruby development. I coming form .Net side
> of things. Is there any way in ruby to verify the type of whatever
> parameter your passing to a method and give the user a good message.


Welcome to the wonderful world of Ruby!

Your Ruby experience will be much more smoothly if you get rid of the
static typing mindset.  It's not the way people use Ruby.  But many people
coming from statically typed languages fear that their Ruby programs will
be totally unsafe if they do not ensure types are enforced.

You'll find a lot of explanations under the term "duck typing".


> For
> example:
>
> def Add_two_numbers(x,y)
>     ....if type of x is not integer
>          throw an error "x was expected to be an integer and is not"
>    .....if type of y is not an integer
>        throw an error "y was expected to be an integer and is not"
> end
>

I once blogged about creating classes which represent numbers.  The central
concept revolves around method #coerce.
http://blog.rubybestpractices.com/posts/rklemme/019-Complete_Numeric_Class.html


In the specific case of your method above, I'd simply do

def add_two_numbers(x, y)
  x.to_int + y.to_int
end

This will reliably fail if x or y do not represent integer values.

When i just hit a bug where i was expecting an array of comments and
> instead a single comment was passed (in the constructor). The code
> exploded with i tried to do "@comments << comments[0]" because @comments
> was not an array with an error message like "undefined function '<<'
> which took me awhile to figure out. Want to try to prevent this in the
> future if possible.
>

Writing tests helps a great deal avoiding that. :-)

Kind regards

robert


-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

--047d7b6da1d26c844b04d9179ef9
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

<div dir=3D"ltr"><br><div class=3D"gmail_extra"><div class=3D"gmail_quote">=
On Fri, Mar 29, 2013 at 5:06 PM, John n/a <span dir=3D"ltr">&lt;<a href=3D"=
mailto:lists@ruby-forum.com" target=3D"_blank">lists@ruby-forum.com</a>&gt;=
</span> wrote:<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-=
left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;p=
adding-left:1ex">Hi everyone. I&#39;m very new to ruby development. I comin=
g form .Net side<br>

of things. Is there any way in ruby to verify the type of whatever<br>
parameter your passing to a method and give the user a good message.</block=
quote><div><br></div><div style>Welcome to the wonderful world of Ruby!</di=
v><div style><br></div><div style>Your Ruby experience will be much more sm=
oothly if you get rid of the static typing mindset. =A0It&#39;s not the way=
 people use Ruby. =A0But many people coming from statically typed languages=
 fear that their Ruby programs will be totally unsafe if they do not ensure=
 types are enforced.</div>
<div style><br></div><div style>You&#39;ll find a lot of explanations under=
 the term &quot;duck typing&quot;.</div><div>=A0</div><blockquote class=3D"=
gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left-width:1px;border=
-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
 For<br>
example:<br>
<br>
def Add_two_numbers(x,y)<br>
=A0 =A0 ....if type of x is not integer<br>
=A0 =A0 =A0 =A0 =A0throw an error &quot;x was expected to be an integer and=
 is not&quot;<br>
=A0 =A0.....if type of y is not an integer<br>
=A0 =A0 =A0 =A0throw an error &quot;y was expected to be an integer and is =
not&quot;<br>
end<br></blockquote><div><br></div><div style>I once blogged about creating=
 classes which represent numbers. =A0The central concept revolves around me=
thod #coerce.</div><div style><a href=3D"http://blog.rubybestpractices.com/=
posts/rklemme/019-Complete_Numeric_Class.html">http://blog.rubybestpractice=
s.com/posts/rklemme/019-Complete_Numeric_Class.html</a>=A0</div>
<div><br></div><div style>In the specific case of your method above, I&#39;=
d simply do</div><div style><br></div><div style>def add_two_numbers(x, y)<=
/div><div style>=A0 x.to_int + y.to_int</div><div style>end</div><div style=
>
<br></div><div style>This will reliably fail if x or y do not represent int=
eger values.</div><div><br></div><blockquote class=3D"gmail_quote" style=3D=
"margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,2=
04,204);border-left-style:solid;padding-left:1ex">

When i just hit a bug where i was expecting an array of comments and<br>
instead a single comment was passed (in the constructor). The code<br>
exploded with i tried to do &quot;@comments &lt;&lt; comments[0]&quot; beca=
use @comments<br>
was not an array with an error message like &quot;undefined function &#39;&=
lt;&lt;&#39;<br>
which took me awhile to figure out. Want to try to prevent this in the<br>
future if possible.=A0<br></blockquote></div><div class=3D"gmail_extra"><br=
></div>Writing tests helps a great deal avoiding that. :-)</div><div class=
=3D"gmail_extra"><br></div><div class=3D"gmail_extra">Kind regards</div><di=
v class=3D"gmail_extra">
<br></div><div class=3D"gmail_extra">robert<br><br clear=3D"all"><div><br><=
/div>-- <br>remember.guy do |as, often| as.you_can - without end<br><a href=
=3D"http://blog.rubybestpractices.com/">http://blog.rubybestpractices.com/<=
/a>
</div></div>

--047d7b6da1d26c844b04d9179ef9--