Why instance variables can be modified through a field reader with the << operator?
Consider the following class.
class Test
attr_reader :word
def initialize(word)
@word = word
end
def append_word(token)
word << token
end
end
Consider a sample usage of the class.
2.4.0 :001 > t = Test.new('Hello')
=> #<Test:0x007f7f09902970 @word="Hello">
2.4.0 :002 > t.append_word(' world!')
=> "Hello world!"
2.4.0 :003 > t.word
=> "Hello world!"
2.4.0 :004 >
I am new to Ruby. I don't understand why I can use the append_word
instance method to modify the instance variable @word
of a Test instance. word
in append_word seems to be a field reader. My understanding is that a field reader is for reading only. How can word << token
in append_word
modify the value of @word
in a Test instance?
ruby
add a comment |
Consider the following class.
class Test
attr_reader :word
def initialize(word)
@word = word
end
def append_word(token)
word << token
end
end
Consider a sample usage of the class.
2.4.0 :001 > t = Test.new('Hello')
=> #<Test:0x007f7f09902970 @word="Hello">
2.4.0 :002 > t.append_word(' world!')
=> "Hello world!"
2.4.0 :003 > t.word
=> "Hello world!"
2.4.0 :004 >
I am new to Ruby. I don't understand why I can use the append_word
instance method to modify the instance variable @word
of a Test instance. word
in append_word seems to be a field reader. My understanding is that a field reader is for reading only. How can word << token
in append_word
modify the value of @word
in a Test instance?
ruby
add a comment |
Consider the following class.
class Test
attr_reader :word
def initialize(word)
@word = word
end
def append_word(token)
word << token
end
end
Consider a sample usage of the class.
2.4.0 :001 > t = Test.new('Hello')
=> #<Test:0x007f7f09902970 @word="Hello">
2.4.0 :002 > t.append_word(' world!')
=> "Hello world!"
2.4.0 :003 > t.word
=> "Hello world!"
2.4.0 :004 >
I am new to Ruby. I don't understand why I can use the append_word
instance method to modify the instance variable @word
of a Test instance. word
in append_word seems to be a field reader. My understanding is that a field reader is for reading only. How can word << token
in append_word
modify the value of @word
in a Test instance?
ruby
Consider the following class.
class Test
attr_reader :word
def initialize(word)
@word = word
end
def append_word(token)
word << token
end
end
Consider a sample usage of the class.
2.4.0 :001 > t = Test.new('Hello')
=> #<Test:0x007f7f09902970 @word="Hello">
2.4.0 :002 > t.append_word(' world!')
=> "Hello world!"
2.4.0 :003 > t.word
=> "Hello world!"
2.4.0 :004 >
I am new to Ruby. I don't understand why I can use the append_word
instance method to modify the instance variable @word
of a Test instance. word
in append_word seems to be a field reader. My understanding is that a field reader is for reading only. How can word << token
in append_word
modify the value of @word
in a Test instance?
ruby
ruby
asked Nov 13 '18 at 3:09
Isaac To
907
907
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
Your @word
references an object in memory. This object happens to be a Hello!
string. Your class does not allow to (easily) set a new object for your @word
instance variable, but nothing currently stops you from modifying the object directly. If you wish for the object to not be modifiable, you could .freeze
it:
class Test
attr_reader :word
def initialize(word)
@word = word.freeze
end
def append_word(token)
word << token
end
end
> Test.new("Hello").append_word("world!")
# FrozenError (can't modify frozen String)
Thanks. Your post answered my question. However, it brought up another. Does Ruby guarantee thatword
, the field reader, refers to the exact same object referred by@word
instead of a copy of the object referred by@word
?
– Isaac To
Nov 13 '18 at 6:43
Yes,attr_reader :word
is the same asdef word; @word; end
– Marcin Kołodziej
Nov 13 '18 at 6:44
1
Technically, Ruby does have some types that are not full objects (by the fact their values are not references), though they behave as objects for most intents and purposes. For example, if@word
is a small integer,word
will return a copy and not a reference (as these objects are never referenced). However, since all such quasi-objects are immutable, there is no situation where a copy will behave differently than a reference, so it's a moot point.
– Amadan
Nov 13 '18 at 7:15
@Amadan true, also worth mentioning that in case of these immutable objects, calling@word
also returns a copy of@word
, therefore adding aattr_reader
does not really change how you interact with underlying value.
– Marcin Kołodziej
Nov 13 '18 at 13:56
@Amadan Does Ruby guarantee that all mutable objects are passed by reference?
– Isaac To
Nov 13 '18 at 22:32
|
show 3 more comments
Your Answer
StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53273208%2fwhy-instance-variables-can-be-modified-through-a-field-reader-with-the-operat%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Your @word
references an object in memory. This object happens to be a Hello!
string. Your class does not allow to (easily) set a new object for your @word
instance variable, but nothing currently stops you from modifying the object directly. If you wish for the object to not be modifiable, you could .freeze
it:
class Test
attr_reader :word
def initialize(word)
@word = word.freeze
end
def append_word(token)
word << token
end
end
> Test.new("Hello").append_word("world!")
# FrozenError (can't modify frozen String)
Thanks. Your post answered my question. However, it brought up another. Does Ruby guarantee thatword
, the field reader, refers to the exact same object referred by@word
instead of a copy of the object referred by@word
?
– Isaac To
Nov 13 '18 at 6:43
Yes,attr_reader :word
is the same asdef word; @word; end
– Marcin Kołodziej
Nov 13 '18 at 6:44
1
Technically, Ruby does have some types that are not full objects (by the fact their values are not references), though they behave as objects for most intents and purposes. For example, if@word
is a small integer,word
will return a copy and not a reference (as these objects are never referenced). However, since all such quasi-objects are immutable, there is no situation where a copy will behave differently than a reference, so it's a moot point.
– Amadan
Nov 13 '18 at 7:15
@Amadan true, also worth mentioning that in case of these immutable objects, calling@word
also returns a copy of@word
, therefore adding aattr_reader
does not really change how you interact with underlying value.
– Marcin Kołodziej
Nov 13 '18 at 13:56
@Amadan Does Ruby guarantee that all mutable objects are passed by reference?
– Isaac To
Nov 13 '18 at 22:32
|
show 3 more comments
Your @word
references an object in memory. This object happens to be a Hello!
string. Your class does not allow to (easily) set a new object for your @word
instance variable, but nothing currently stops you from modifying the object directly. If you wish for the object to not be modifiable, you could .freeze
it:
class Test
attr_reader :word
def initialize(word)
@word = word.freeze
end
def append_word(token)
word << token
end
end
> Test.new("Hello").append_word("world!")
# FrozenError (can't modify frozen String)
Thanks. Your post answered my question. However, it brought up another. Does Ruby guarantee thatword
, the field reader, refers to the exact same object referred by@word
instead of a copy of the object referred by@word
?
– Isaac To
Nov 13 '18 at 6:43
Yes,attr_reader :word
is the same asdef word; @word; end
– Marcin Kołodziej
Nov 13 '18 at 6:44
1
Technically, Ruby does have some types that are not full objects (by the fact their values are not references), though they behave as objects for most intents and purposes. For example, if@word
is a small integer,word
will return a copy and not a reference (as these objects are never referenced). However, since all such quasi-objects are immutable, there is no situation where a copy will behave differently than a reference, so it's a moot point.
– Amadan
Nov 13 '18 at 7:15
@Amadan true, also worth mentioning that in case of these immutable objects, calling@word
also returns a copy of@word
, therefore adding aattr_reader
does not really change how you interact with underlying value.
– Marcin Kołodziej
Nov 13 '18 at 13:56
@Amadan Does Ruby guarantee that all mutable objects are passed by reference?
– Isaac To
Nov 13 '18 at 22:32
|
show 3 more comments
Your @word
references an object in memory. This object happens to be a Hello!
string. Your class does not allow to (easily) set a new object for your @word
instance variable, but nothing currently stops you from modifying the object directly. If you wish for the object to not be modifiable, you could .freeze
it:
class Test
attr_reader :word
def initialize(word)
@word = word.freeze
end
def append_word(token)
word << token
end
end
> Test.new("Hello").append_word("world!")
# FrozenError (can't modify frozen String)
Your @word
references an object in memory. This object happens to be a Hello!
string. Your class does not allow to (easily) set a new object for your @word
instance variable, but nothing currently stops you from modifying the object directly. If you wish for the object to not be modifiable, you could .freeze
it:
class Test
attr_reader :word
def initialize(word)
@word = word.freeze
end
def append_word(token)
word << token
end
end
> Test.new("Hello").append_word("world!")
# FrozenError (can't modify frozen String)
answered Nov 13 '18 at 3:13
Marcin Kołodziej
4,2611315
4,2611315
Thanks. Your post answered my question. However, it brought up another. Does Ruby guarantee thatword
, the field reader, refers to the exact same object referred by@word
instead of a copy of the object referred by@word
?
– Isaac To
Nov 13 '18 at 6:43
Yes,attr_reader :word
is the same asdef word; @word; end
– Marcin Kołodziej
Nov 13 '18 at 6:44
1
Technically, Ruby does have some types that are not full objects (by the fact their values are not references), though they behave as objects for most intents and purposes. For example, if@word
is a small integer,word
will return a copy and not a reference (as these objects are never referenced). However, since all such quasi-objects are immutable, there is no situation where a copy will behave differently than a reference, so it's a moot point.
– Amadan
Nov 13 '18 at 7:15
@Amadan true, also worth mentioning that in case of these immutable objects, calling@word
also returns a copy of@word
, therefore adding aattr_reader
does not really change how you interact with underlying value.
– Marcin Kołodziej
Nov 13 '18 at 13:56
@Amadan Does Ruby guarantee that all mutable objects are passed by reference?
– Isaac To
Nov 13 '18 at 22:32
|
show 3 more comments
Thanks. Your post answered my question. However, it brought up another. Does Ruby guarantee thatword
, the field reader, refers to the exact same object referred by@word
instead of a copy of the object referred by@word
?
– Isaac To
Nov 13 '18 at 6:43
Yes,attr_reader :word
is the same asdef word; @word; end
– Marcin Kołodziej
Nov 13 '18 at 6:44
1
Technically, Ruby does have some types that are not full objects (by the fact their values are not references), though they behave as objects for most intents and purposes. For example, if@word
is a small integer,word
will return a copy and not a reference (as these objects are never referenced). However, since all such quasi-objects are immutable, there is no situation where a copy will behave differently than a reference, so it's a moot point.
– Amadan
Nov 13 '18 at 7:15
@Amadan true, also worth mentioning that in case of these immutable objects, calling@word
also returns a copy of@word
, therefore adding aattr_reader
does not really change how you interact with underlying value.
– Marcin Kołodziej
Nov 13 '18 at 13:56
@Amadan Does Ruby guarantee that all mutable objects are passed by reference?
– Isaac To
Nov 13 '18 at 22:32
Thanks. Your post answered my question. However, it brought up another. Does Ruby guarantee that
word
, the field reader, refers to the exact same object referred by @word
instead of a copy of the object referred by @word
?– Isaac To
Nov 13 '18 at 6:43
Thanks. Your post answered my question. However, it brought up another. Does Ruby guarantee that
word
, the field reader, refers to the exact same object referred by @word
instead of a copy of the object referred by @word
?– Isaac To
Nov 13 '18 at 6:43
Yes,
attr_reader :word
is the same as def word; @word; end
– Marcin Kołodziej
Nov 13 '18 at 6:44
Yes,
attr_reader :word
is the same as def word; @word; end
– Marcin Kołodziej
Nov 13 '18 at 6:44
1
1
Technically, Ruby does have some types that are not full objects (by the fact their values are not references), though they behave as objects for most intents and purposes. For example, if
@word
is a small integer, word
will return a copy and not a reference (as these objects are never referenced). However, since all such quasi-objects are immutable, there is no situation where a copy will behave differently than a reference, so it's a moot point.– Amadan
Nov 13 '18 at 7:15
Technically, Ruby does have some types that are not full objects (by the fact their values are not references), though they behave as objects for most intents and purposes. For example, if
@word
is a small integer, word
will return a copy and not a reference (as these objects are never referenced). However, since all such quasi-objects are immutable, there is no situation where a copy will behave differently than a reference, so it's a moot point.– Amadan
Nov 13 '18 at 7:15
@Amadan true, also worth mentioning that in case of these immutable objects, calling
@word
also returns a copy of @word
, therefore adding a attr_reader
does not really change how you interact with underlying value.– Marcin Kołodziej
Nov 13 '18 at 13:56
@Amadan true, also worth mentioning that in case of these immutable objects, calling
@word
also returns a copy of @word
, therefore adding a attr_reader
does not really change how you interact with underlying value.– Marcin Kołodziej
Nov 13 '18 at 13:56
@Amadan Does Ruby guarantee that all mutable objects are passed by reference?
– Isaac To
Nov 13 '18 at 22:32
@Amadan Does Ruby guarantee that all mutable objects are passed by reference?
– Isaac To
Nov 13 '18 at 22:32
|
show 3 more comments
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Some of your past answers have not been well-received, and you're in danger of being blocked from answering.
Please pay close attention to the following guidance:
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53273208%2fwhy-instance-variables-can-be-modified-through-a-field-reader-with-the-operat%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown