# (String \* Fixnum) and (Fixnum \* String)

**URL:** <https://www.ruby-forum.com/t/string-fixnum-and-fixnum-string/112596>\
**Category:** Ruby\
**Created:** [August 21, 2007, 8:13am UTC](https://www.ruby-forum.com/t/string-fixnum-and-fixnum-string/112596 "2007-08-21T08:13:17Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![dan](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/eada6e/32.png) [@dan](https://www.ruby-forum.com/u/dan)\
**Post date:** [August 21, 2007, 8:13am UTC](https://www.ruby-forum.com/t/string-fixnum-and-fixnum-string/112596/1 "2007-08-21T08:13:17Z")

</div>

Just a small quick question:

String \* Fixnum works:

"test " \* 4  
=\> test test test test

while Fixnum \* String doesn’t:

4 \* "test "  
TypeError: String can’t be coerced into  
Fixnum  
from (irb):19:in  
`\*’  
from (irb):19

I understand that ruby being strongly typed means you can only do  
“sensible”  
things with the types you are working with. However, aren’t the examples  
above pretty much equivalent? or is it a precedence thing? Trying to  
answer  
my own question is it because the “_" operator for a Fixnum only accepts  
another Fixnum/Bignum, while the "_” operator for a String only allows a  
Fixnum, because it sure doesn’t let you do String \* String (and why  
would  
you really).

Someone please help me grasp this 🙂 Thanks

---

<div class="post-metadata">

**Author:** ![dan](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/eada6e/32.png) [@dan](https://www.ruby-forum.com/u/dan)\
**Post date:** [August 21, 2007, 8:33am UTC](https://www.ruby-forum.com/t/string-fixnum-and-fixnum-string/112596/2 "2007-08-21T08:33:20Z")

</div>

On 21 Aug 2007, at 15:12, Dan wrote:

> 4 \* "test "  
> above pretty much equivalent? or is it a precedence thing? Trying  
> to answer  
> my own question is it because the “_" operator for a Fixnum only  
> accepts  
> another Fixnum/Bignum, while the "_” operator for a String only  
> allows a  
> Fixnum, because it sure doesn’t let you do String \* String (and why  
> would  
> you really).
> 
> Someone please help me grasp this 🙂 Thanks

You’ve got it I think. In the first instance you call the String#\*  
method. This accepts an Integer argument and returns a String:

## --------------------------------------------------------------- String#\* str \* integer =\> new\_str

```
  Copy---Returns a new +String+ containing _integer_ copies of the
  receiver.

     "Ho! " * 3 #=> "Ho! Ho! Ho! "

```

The second time you call the Fixnum#\* method which accepts Numeric  
arguments (not Strings).

## --------------------------------------------------------------- Fixnum#\* fix \* numeric =\> numeric\_result

```
  Performs multiplication: the class of the resulting object depends
  on the class of +numeric+ and on the magnitude of the result.

```

This being Ruby, it is easy (but maybe dangerous) to extend the  
Fixnum class to perform as you like:

irb(main):001:0\> class Fixnum  
irb(main):002:1\> alias mult \*  
irb(main):003:1\* def \*(a)  
irb(main):004:2\> return a \* self if a.is\_a?(String)  
irb(main):005:2\> return mult(a)  
irb(main):006:2\> end  
irb(main):007:1\> end  
=\> nil  
irb(main):008:0\> 2 \* 2  
=\> 4  
irb(main):009:0\> 2 \* “foo”  
=\> “foofoo”

Alex G.

Bioinformatics Center  
Kyoto University

---

<div class="post-metadata">

**Author:** ![dan](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/eada6e/32.png) [@dan](https://www.ruby-forum.com/u/dan)\
**Post date:** [August 21, 2007, 8:59am UTC](https://www.ruby-forum.com/t/string-fixnum-and-fixnum-string/112596/3 "2007-08-21T08:59:24Z")

</div>

On 21 Aug 2007, at 15:12, Dan wrote:

> Fixnum, because it sure doesn’t let you do String \* String (and why  
> would  
> you really).

To clarify my previous answer, the important thing is to realise that  
most ‘operators’ in Ruby are just methods that look funny. So

3 \* 2

Is just another way of writing

3.\* 2

or

3.send(:\*,2)

And hence ‘foo’ \* 2 is very different to 2 \* ‘foo’ in terms of the  
underlying method that is called.  
Alex G.

Bioinformatics Center  
Kyoto University

---

<div class="post-metadata">

**Author:** ![dan](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/eada6e/32.png) [@dan](https://www.ruby-forum.com/u/dan)\
**Post date:** [August 21, 2007, 9:54am UTC](https://www.ruby-forum.com/t/string-fixnum-and-fixnum-string/112596/4 "2007-08-21T09:54:28Z")

</div>

Dan wrote:

> Just a small quick question:
> 
> String \* Fixnum works:  
> …  
> while Fixnum \* String doesn’t:

Think of it like this:  
4_3 = 4+4+4 (4 added 3 times) = 12  
3_4 = 3+3+3+3 (3 added 4 times) = 12  
Those are equivalent because x added y times and y added x times always  
give  
the same result (x and y being numbers).

“bla”\*3=“bla”+“bla”+“bla” (“bla” added 3 times)=“blablabla”  
But what would 3 \* “bla” be? 3 added “bla” times? What does that mean?

HTH,  
Sebastian

---

<div class="post-metadata">

**Author:** ![dan](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/eada6e/32.png) [@dan](https://www.ruby-forum.com/u/dan)\
**Post date:** [August 21, 2007, 9:01am UTC](https://www.ruby-forum.com/t/string-fixnum-and-fixnum-string/112596/5 "2007-08-21T09:01:24Z")

</div>

Dan wrote:

> 4 \* "test "  
> another Fixnum/Bignum, while the “\*” operator for a String only allows a  
> Fixnum, because it sure doesn’t let you do String \* String (and why would  
> you really).
> 
> Someone please help me grasp this 🙂 Thanks

As I read it in Chris P.'s excellent ‘How to Program’, when you do  
string \* fixnum, you’re telling the string to multiply itself ‘fixnum’  
times - the string knows how to do that.

When you do fixnum \* string, you’re trying to ask the a fixnum to  
multiply itself string times - that makes no sense. Thus, it’s not  
allowed.

Cheers,  
Mohit.  
8/21/2007 | 3:00 PM.

P.S. I’m new to the group - so, I’ll use this email to piggyback and say  
HI to everyone!