We have do-and-replace functions like map!, reject!, reverse!, rotate!. Also we have binary operations in short form like +=, -=.
Do we have something for mathematical round? We need to use a = a.round, and it's a bit weird for me to repeat the variable name. Do you know how to shorten it?
OK, smart guys have already explained, why there is no syntactic sugar for Float#round. Just out of curiosity I’m gonna show, how you might implement this sugar yourself [partially]. Since Float class has no ~# method defined, and you do rounding quite often, you might monkeypatch Float class:
class Float
def ~#
self.round # self is redundant, left just for clarity
end
end
or, in this simple case, just (credits to #sawa):
alias_method :~#, :round
and now:
~5.2
#⇒ 5
a = 2.45 && ~a
#⇒ 2
Since Numerics are immutable, it’s still impossible to modify it inplace, but the above might save you four keyboard hits per rounding.
As for destructive methods, it is impossible since numerals are immutable, and it would not make sense. Would you want a numeral 5.2 that behaves as 5?
As for syntax sugar, it would be a mess if every single method had one. So there isn't. And since syntax sugar is defined in the core level, you cannot do anything in an ordinary Ruby script to create a new one.
Ruby's numeric types are immutable: they are value objects. Therefore you won't find any methods that mutate a number in place.
Because the numeric types are immutable, certain optimizations are possible that would not be possible with mutable numbers. In c-ruby, for example, a reference, which may point to any kind of object, is normally a pointer to an object. But if the reference is to a Fixnum, then the reference contains the integer itself, rather than pointing to an instance of Fixnum. Ruby does a number of magic tricks to hide this optimization, making it appear that an integer really is an instance of a Fixnum.
To make numbers mutable would make this optimization impossible, so I don't expect that Ruby will ever have mutable numeric types.
Related
I'm learning Ruby and I've seen a couple of methods that are confusing me a bit, particularly to_s vs to_str (and similarly, to_i/to_int, to_a/to_ary, & to_h/to_hash). What I've read explains that the shorter form (e.g. to_s) are for explicit conversions while the longer form are for implicit conversions.
I don't really understand how to_str would actually be used. Would something other than a String ever define to_str? Can you give a practical application for this method?
Note first that all of this applies to each pair of “short” (e.g. to_s/to_i/to_a/to_h) vs. “long” (e.g. to_str/to_int/to_ary/to_hash) coercion methods in Ruby (for their respective types) as they all have the same semantics.
They have different meanings. You should not implement to_str unless your object acts like a string, rather than just being representable by a string. The only core class that implements to_str is String itself.
From Programming Ruby (quoted from this blog post, which is worth reading all of):
[to_i and to_s] are not particularly strict: if an object has some kind of decent representation as a string, for example, it will probably have a to_s method… [to_int and to_str] are strict conversion functions: you implement them only if [your] object can naturally be used every place a string or an integer could be used.
Older Ruby documentation from the Pickaxe has this to say:
Unlike to_s, which is supported by almost all classes, to_str is normally implemented only by those classes that act like strings.
For example, in addition to Integer, both Float & Numeric implement to_int (to_i's equivalent of to_str) because both of them can readily substituted for an Integer (they are all actually numbers). Unless your class has a similarly tight relationship with String, you should not implement to_str.
To understand if you should use/implement to_s/to_str, let's look at some exemples. It is revealing to consider when these method fail.
1.to_s # returns "1"
Object.new.to_s # returns "#<Object:0x4932990>"
1.to_str # raises NoMethodError
Object.new.to_str # raises NoMethodError
As we can see, to_s is happy to turn any object into a string. On the other hand, to_str raises an error when its parameter does not look like a string.
Now let us look at Array#join.
[1,2].join(',') # returns "1,2"
[1,2].join(3) # fails, the argument does not look like a valid separator.
It is useful that Array#join converts to string the items in the array (whatever they really are) before joining them, so Array#join calls to_s on them.
However, the separator is supposed to be a string -- someone calling [1,2].join(3) is likely to be making a mistake. This is why Array#join calls to_str on the separator.
The same principle seems to hold for the other methods. Consider to_a/to_ary on a hash:
{1,2}.to_a # returns [[1, 2]], an array that describes the hash
{1,2}.to_ary # fails, because a hash is not really an array.
In summary, here is how I see it:
call to_s to get a string that describes the object.
call to_str to verify that an object really acts like a string.
implement to_s when you can build a string that describes your object.
implement to_str when your object can fully behave like a string.
I think a case when you could implement to_str yourself is maybe a ColoredString class -- a string that has a color attached to it. If it seems clear to you that passing a colored comma to join is not a mistake and should result in "1,2" (even though that string would not be colored), then do implement to_str on ColoredString.
Zverok has a great easily understandable article about when to use what (explained with to_h and to_hash).
It has to do whether your Object implementing those methods can be converted to a string
-> use to_s
or it is a type of some (enhanced) string
-> use to_str
I've seen a meaningful usage of to_hash in practice for the Configuration class in the gem 'configuration' (GitHub and Configuration.rb)
It represents -- as the name says -- the provided configuration, which in fact is a kind of hash (with additional features), rather than being convertible to one.
The pre/post increment/decrement operator (++ and --) are pretty standard programing language syntax (for procedural and object-oriented languages, at least).
Why doesn't Ruby support them? I understand you could accomplish the same thing with += and -=, but it just seems oddly arbitrary to exclude something like that, especially since it's so concise and conventional.
Example:
i = 0 #=> 0
i += 1 #=> 1
i #=> 1
i++ #=> expect 2, but as far as I can tell,
#=> irb ignores the second + and waits for a second number to add to i
I understand Fixnum is immutable, but if += can just instanciate a new Fixnum and set it, why not do the same for ++?
Is consistency in assignments containing the = character the only reason for this, or am I missing something?
Here is how Matz(Yukihiro Matsumoto) explains it in an old thread:
Hi,
In message "[ruby-talk:02706] X++?"
on 00/05/10, Aleksi Niemelä <aleksi.niemela#cinnober.com> writes:
|I got an idea from http://www.pragprog.com:8080/rubyfaq/rubyfaq-5.html#ss5.3
|and thought to try. I didn't manage to make "auto(in|de)crement" working so
|could somebody help here? Does this contain some errors or is the idea
|wrong?
(1) ++ and -- are NOT reserved operator in Ruby.
(2) C's increment/decrement operators are in fact hidden assignment.
They affect variables, not objects. You cannot accomplish
assignment via method. Ruby uses +=/-= operator instead.
(3) self cannot be a target of assignment. In addition, altering
the value of integer 1 might cause severe confusion throughout
the program.
matz.
One reason is that up to now every assignment operator (i.e. an operator which changes a variable) has a = in it. If you add ++ and --, that's no longer the case.
Another reason is that the behavior of ++ and -- often confuse people. Case in point: The return value of i++ in your example would actually be 1, not 2 (the new value of i would be 2, however).
It's not conventional in OO languages. In fact, there is no ++ in Smalltalk, the language that coined the term "object-oriented programming" (and the language Ruby is most strongly influenced by). What you mean is that it's conventional in C and languages closely imitating C. Ruby does have a somewhat C-like syntax, but it isn't slavish in adhering to C traditions.
As for why it isn't in Ruby: Matz didn't want it. That's really the ultimate reason.
The reason no such thing exists in Smalltalk is because it's part of the language's overriding philosophy that assigning a variable is fundamentally a different kind of thing than sending a message to an object — it's on a different level. This thinking probably influenced Matz in designing Ruby.
It wouldn't be impossible to include it in Ruby — you could easily write a preprocessor that transforms all ++ into +=1. but evidently Matz didn't like the idea of an operator that did a "hidden assignment." It also seems a little strange to have an operator with a hidden integer operand inside of it. No other operator in the language works that way.
I think there's another reason: ++ in Ruby wouldn't be remotely useful as in C and its direct successors.
The reason being, the for keyword: while it's essential in C, it's mostly superfluous in Ruby. Most of the iteration in Ruby is done through Enumerable methods, such as each and map when iterating through some data structure, and Fixnum#times method, when you need to loop an exact number of times.
Actually, as far as I have seen, most of the time +=1 is used by people freshly migrated to Ruby from C-style languages.
In short, it's really questionable if methods ++ and -- would be used at all.
You can define a .+ self-increment operator:
class Variable
def initialize value = nil
#value = value
end
attr_accessor :value
def method_missing *args, &blk
#value.send(*args, &blk)
end
def to_s
#value.to_s
end
# pre-increment ".+" when x not present
def +(x = nil)
x ? #value + x : #value += 1
end
def -(x = nil)
x ? #value - x : #value -= 1
end
end
i = Variable.new 5
puts i #=> 5
# normal use of +
puts i + 4 #=> 9
puts i #=> 5
# incrementing
puts i.+ #=> 6
puts i #=> 6
More information on "class Variable" is available in "Class Variable to increment Fixnum objects".
I think Matz' reasoning for not liking them is that it actually replaces the variable with a new one.
ex:
a = SomeClass.new
def a.go
'hello'
end
# at this point, you can call a.go
# but if you did an a++
# that really means a = a + 1
# so you can no longer call a.go
# as you have lost your original
Now if somebody could convince him that it should just call #succ! or what not, that would make more sense, and avoid the problem. You can suggest it on ruby core.
And in the words of David Black from his book "The Well-Grounded Rubyist":
Some objects in Ruby are stored in variables as immediate values. These include
integers, symbols (which look like :this), and the special objects true, false, and
nil. When you assign one of these values to a variable (x = 1), the variable holds
the value itself, rather than a reference to it.
In practical terms, this doesn’t matter (and it will often be left as implied, rather than
spelled out repeatedly, in discussions of references and related topics in this book).
Ruby handles the dereferencing of object references automatically; you don’t have to
do any extra work to send a message to an object that contains, say, a reference to
a string, as opposed to an object that contains an immediate integer value.
But the immediate-value representation rule has a couple of interesting ramifications,
especially when it comes to integers. For one thing, any object that’s represented
as an immediate value is always exactly the same object, no matter how many
variables it’s assigned to. There’s only one object 100, only one object false, and
so on.
The immediate, unique nature of integer-bound variables is behind Ruby’s lack of
pre- and post-increment operators—which is to say, you can’t do this in Ruby:
x = 1
x++ # No such operator
The reason is that due to the immediate presence of 1 in x, x++ would be like 1++,
which means you’d be changing the number 1 to the number 2—and that makes
no sense.
Some objects in Ruby are stored in variables as immediate values. These include integers, symbols (which look like :this), and the special objects true, false, and nil. When you assign one of these values to a variable (x = 1), the variable holds the value itself, rather than a reference to it.
Any object that’s represented as an immediate value is always exactly the same object, no matter how many variables it’s assigned to. There’s only one object 100, only one object false, and so on.
The immediate, unique nature of integer-bound variables is behind Ruby’s lack of pre-and post-increment operators—which is to say, you can’t do this in Ruby:
x=1
x++ # No such operator
The reason is that due to the immediate presence of 1 in x, x++ would be like 1++, which means you’d be changing the number 1 to the number 2—and that makes no sense.
Couldn't this be achieved by adding a new method to the fixnum or Integer class?
$ ruby -e 'numb=1;puts numb.next'
returns 2
"Destructive" methods seem to be appended with ! to warn possible users, so adding a new method called next! would pretty much do what was requested ie.
$ ruby -e 'numb=1; numb.next!; puts numb'
returns 2 (since numb has been incremented)
Of course, the next! method would have to check that the object was an integer variable and not a real number, but this should be available.
I'm not actually going to use this in anything in case it does actually work but is it possible to redefine 0 to act as 1 in Ruby and 1 to act as 0? Where does FixNum actually hold its value?
No, I don't think so. I'd be very suprised if you managed to. If you start overriding Fixnum's methods/operators, you maaaybe might get near that (i.e. override + so that 1+5 => 5, 0+5 => 6 etc), but you will not get full replacement of literal '0' with value 1. At least marshalling to native would expose the real 0 value of the Fixnum(0).
To be honest, I'm not really sure if you can even override the core operations like + op on a Fixnum. That could break so many things..
As far as I remember from 1.8.3 source, simple integers and doubles are held right inside a 'value' and are copied all around *). There is no singular "0", "1" or "1000" value. There is no extra dereference that would allow you to swap all the values with one shot. I doubt it changed in 1.9 and I doubt anyone got any weird idea about that in 2.0. But I don't actually know. Still, that would be strange. No platform I know interns integers and floatings.. Strings, sometimes array literals, but numbers?
So, sorry, no #define true false jokes :)
--
*) clarification from Jörg W Mittag (thanks, this is exactly what I was referring to):
(..) Fixnums do not have a place in memory, their pointer value is "magic" (in that it cannot possibly occur in a Ruby program) and treated specially by the runtime system. Read up on "tagged pointer representation", e.g. here.
Assignment does not alias Fixnum objects. There is effectively only one Fixnum object instance for any given integer value, so, for example, you cannot add a singleton method to a Fixnum. Any attempt to add a singleton method to a Fixnum object will raise a TypeError. Source
That pretty much means you can't edit a Fixnum and therefor not redefine 0 or 1 in native ruby.
Though as these Fixnums are also Objects they have unique object id's that cleary reference them somewhere in the memory. See BasicObject#__id__
If you can locate the memory space where 0 and 1 objects are and switch these, you should have effectivle switched 0 and 1 behavior in ruby as now either will reference the other object.
So to answer your question: No redefining Fixnums is not possible in Ruby, switching their behaviour should be possible though.
The pre/post increment/decrement operator (++ and --) are pretty standard programing language syntax (for procedural and object-oriented languages, at least).
Why doesn't Ruby support them? I understand you could accomplish the same thing with += and -=, but it just seems oddly arbitrary to exclude something like that, especially since it's so concise and conventional.
Example:
i = 0 #=> 0
i += 1 #=> 1
i #=> 1
i++ #=> expect 2, but as far as I can tell,
#=> irb ignores the second + and waits for a second number to add to i
I understand Fixnum is immutable, but if += can just instanciate a new Fixnum and set it, why not do the same for ++?
Is consistency in assignments containing the = character the only reason for this, or am I missing something?
Here is how Matz(Yukihiro Matsumoto) explains it in an old thread:
Hi,
In message "[ruby-talk:02706] X++?"
on 00/05/10, Aleksi Niemelä <aleksi.niemela#cinnober.com> writes:
|I got an idea from http://www.pragprog.com:8080/rubyfaq/rubyfaq-5.html#ss5.3
|and thought to try. I didn't manage to make "auto(in|de)crement" working so
|could somebody help here? Does this contain some errors or is the idea
|wrong?
(1) ++ and -- are NOT reserved operator in Ruby.
(2) C's increment/decrement operators are in fact hidden assignment.
They affect variables, not objects. You cannot accomplish
assignment via method. Ruby uses +=/-= operator instead.
(3) self cannot be a target of assignment. In addition, altering
the value of integer 1 might cause severe confusion throughout
the program.
matz.
One reason is that up to now every assignment operator (i.e. an operator which changes a variable) has a = in it. If you add ++ and --, that's no longer the case.
Another reason is that the behavior of ++ and -- often confuse people. Case in point: The return value of i++ in your example would actually be 1, not 2 (the new value of i would be 2, however).
It's not conventional in OO languages. In fact, there is no ++ in Smalltalk, the language that coined the term "object-oriented programming" (and the language Ruby is most strongly influenced by). What you mean is that it's conventional in C and languages closely imitating C. Ruby does have a somewhat C-like syntax, but it isn't slavish in adhering to C traditions.
As for why it isn't in Ruby: Matz didn't want it. That's really the ultimate reason.
The reason no such thing exists in Smalltalk is because it's part of the language's overriding philosophy that assigning a variable is fundamentally a different kind of thing than sending a message to an object — it's on a different level. This thinking probably influenced Matz in designing Ruby.
It wouldn't be impossible to include it in Ruby — you could easily write a preprocessor that transforms all ++ into +=1. but evidently Matz didn't like the idea of an operator that did a "hidden assignment." It also seems a little strange to have an operator with a hidden integer operand inside of it. No other operator in the language works that way.
I think there's another reason: ++ in Ruby wouldn't be remotely useful as in C and its direct successors.
The reason being, the for keyword: while it's essential in C, it's mostly superfluous in Ruby. Most of the iteration in Ruby is done through Enumerable methods, such as each and map when iterating through some data structure, and Fixnum#times method, when you need to loop an exact number of times.
Actually, as far as I have seen, most of the time +=1 is used by people freshly migrated to Ruby from C-style languages.
In short, it's really questionable if methods ++ and -- would be used at all.
You can define a .+ self-increment operator:
class Variable
def initialize value = nil
#value = value
end
attr_accessor :value
def method_missing *args, &blk
#value.send(*args, &blk)
end
def to_s
#value.to_s
end
# pre-increment ".+" when x not present
def +(x = nil)
x ? #value + x : #value += 1
end
def -(x = nil)
x ? #value - x : #value -= 1
end
end
i = Variable.new 5
puts i #=> 5
# normal use of +
puts i + 4 #=> 9
puts i #=> 5
# incrementing
puts i.+ #=> 6
puts i #=> 6
More information on "class Variable" is available in "Class Variable to increment Fixnum objects".
I think Matz' reasoning for not liking them is that it actually replaces the variable with a new one.
ex:
a = SomeClass.new
def a.go
'hello'
end
# at this point, you can call a.go
# but if you did an a++
# that really means a = a + 1
# so you can no longer call a.go
# as you have lost your original
Now if somebody could convince him that it should just call #succ! or what not, that would make more sense, and avoid the problem. You can suggest it on ruby core.
And in the words of David Black from his book "The Well-Grounded Rubyist":
Some objects in Ruby are stored in variables as immediate values. These include
integers, symbols (which look like :this), and the special objects true, false, and
nil. When you assign one of these values to a variable (x = 1), the variable holds
the value itself, rather than a reference to it.
In practical terms, this doesn’t matter (and it will often be left as implied, rather than
spelled out repeatedly, in discussions of references and related topics in this book).
Ruby handles the dereferencing of object references automatically; you don’t have to
do any extra work to send a message to an object that contains, say, a reference to
a string, as opposed to an object that contains an immediate integer value.
But the immediate-value representation rule has a couple of interesting ramifications,
especially when it comes to integers. For one thing, any object that’s represented
as an immediate value is always exactly the same object, no matter how many
variables it’s assigned to. There’s only one object 100, only one object false, and
so on.
The immediate, unique nature of integer-bound variables is behind Ruby’s lack of
pre- and post-increment operators—which is to say, you can’t do this in Ruby:
x = 1
x++ # No such operator
The reason is that due to the immediate presence of 1 in x, x++ would be like 1++,
which means you’d be changing the number 1 to the number 2—and that makes
no sense.
Some objects in Ruby are stored in variables as immediate values. These include integers, symbols (which look like :this), and the special objects true, false, and nil. When you assign one of these values to a variable (x = 1), the variable holds the value itself, rather than a reference to it.
Any object that’s represented as an immediate value is always exactly the same object, no matter how many variables it’s assigned to. There’s only one object 100, only one object false, and so on.
The immediate, unique nature of integer-bound variables is behind Ruby’s lack of pre-and post-increment operators—which is to say, you can’t do this in Ruby:
x=1
x++ # No such operator
The reason is that due to the immediate presence of 1 in x, x++ would be like 1++, which means you’d be changing the number 1 to the number 2—and that makes no sense.
Couldn't this be achieved by adding a new method to the fixnum or Integer class?
$ ruby -e 'numb=1;puts numb.next'
returns 2
"Destructive" methods seem to be appended with ! to warn possible users, so adding a new method called next! would pretty much do what was requested ie.
$ ruby -e 'numb=1; numb.next!; puts numb'
returns 2 (since numb has been incremented)
Of course, the next! method would have to check that the object was an integer variable and not a real number, but this should be available.
So as I understand it, the === operator tests to see if the RHS object is a member of the LHS object. That makes sense. But how does this work in Ruby? I'm looking at the Ruby docs and I only see === defined in Object, I don't see it in Integer itself. Is it just not documented?
Integer is a class, which (at least in Ruby) means that it is just a boring old normal object like any other object, which just happens to be an instance of the Class class (instead of, say, Object or String or MyWhateverFoo).
Class in turn is a subclass of Module (although arguably it shouldn't be, because it violates the Liskov Substition Principle, but that is a discussion for another forum, and is also a dead horse that has already been beaten many many times). And in Module#=== you will find the definition you are looking for, which Class inherits from Module and instances of Class (like Integer) understand.
Module#=== is basically defined symmetric to Object#kind_of?, it returns true if its argument is an instance of itself. So, 3 is an instance of Integer, therefore Integer === 3 returns true, just as 3.kind_of?(Integer) would.
So as I understand it, the === operator tests to see if the RHS object is a member of the LHS object.
Not necessarily. === is a method, just like any other method. It does whatever I want it to do. And in some cases the "is member of" analogy breaks down. In this case it is already pretty hard to swallow. If you are a hardcore type theory freak, then viewing a type as a set and instances of that type as members of a set is totally natural. And of course for Array and Hash the definition of "member" is also obvious.
But what about Regexp? Again, if you are formal languages buff and know your Chomsky backwards, then interpreting a Regexp as an infinite set of words and Strings as members of that set feels completely natural, but if not, then it sounds kind of weird.
So far, I have failed to come up with a concise description of precisely what === means. In fact, I haven't even come up with a good name for it. It is usually called the triple equals operator, threequals operator or case equality operator, but I strongly dislike those names, because it has absolutely nothing to do with equality.
So, what does it do? The best I have come up with is: imagine you are making a table, and one of the column headers is Integer. Would it make sense to write 3 in that column? If one of the column headers is /ab*a/, would it make sense to write 'abbbba' in that column?
Based on that definition, it could be called the subsumption operator, but that's even worse than the other examples ...
It's defined on Module, which Class is a subclass of, which Integer is an instance of.
In other words, when you run Integer === 3, you're calling '===' (with the parameter 3) on the object referred to to by the constant Integer, which is an instance of the class named Class. Since Class is a subclass of Module and doesn't define its own ===, you get the implementation of === defined on Module.
See the API docs for Module for more information.
Umm, Integer is a subclass of Object.