It is the ternary operator, and it works like in C (the parenthesis are not required). It’s an expression that works like: if_this_is_a_true_value ? then_the_result_is_this : else_it_is_this However, in Ruby, if is also an expression so: if a then b else c end === a ? b : c, except for precedence issues. Both are … Read more
What you want to do is called dynamic dispatch. It’s very easy in Ruby, just use public_send: method_name=”foobar” obj.public_send(method_name) if obj.respond_to? method_name If the method is private/protected, use send instead, but prefer public_send. This is a potential security risk if the value of method_name comes from the user. To prevent vulnerabilities, you should validate which … Read more
There’s a simple command built-in that will pull it: rvm implode This will remove the rvm/ directory and all the rubies built within it. In order to remove the final trace of rvm, you need to remove the rvm gem, too, if you installed that: gem uninstall rvm There may be elements left over from … Read more
In general, methods that end in ! indicate that the method will modify the object it’s called on. Ruby calls these as “dangerous methods” because they change state that someone else might have a reference to. Here’s a simple example for strings: foo = “A STRING” # a string called foo foo.downcase! # modifies foo … Read more
Again and again we see questions asking about reading a text file to process it line-by-line, that use variations of read, or readlines, which pull the entire file into memory in one action. The documentation for read says: Opens the file, optionally seeks to the given offset, then returns length bytes (defaulting to the rest … Read more
You cannot dynamically create local variables in Ruby 1.9+ (you could in Ruby 1.8 via eval): eval ‘foo = “bar”‘ foo # NameError: undefined local variable or method `foo’ for main:Object They can be used within the eval-ed code itself, though: eval ‘foo = “bar”; foo + “baz”‘ #=> “barbaz” Ruby 2.1 added local_variable_set, but … Read more
EDIT: It has been 9 years since I originally wrote this answer, and it deserves some cosmetic surgery to keep it current. You can see the last version before the edit here. You can’t call the overwritten method by name or keyword. That’s one of the many reasons why monkey patching should be avoided and … Read more
Your question is wrong, so to speak. What’s happening here isn’t “ampersand and colon”, it’s “ampersand and object”. The colon in this case is for the symbol. So, there’s & and there’s :foo. The & calls to_proc on the object, and passes it as a block to the method. In Ruby, to_proc is implemented on … Read more
This explanation is based on a commented Ruby script from a friend of mine. If you want to improve the script, feel free to update it at the link. First, note that when Ruby calls out to a shell, it typically calls /bin/sh, not Bash. Some Bash syntax is not supported by /bin/sh on all … Read more
a ||= b is a conditional assignment operator. It means: if a is undefined or falsey, then evaluate b and set a to the result. Otherwise (if a is defined and evaluates to truthy), then b is not evaluated, and no assignment takes place. For example: a ||= nil # => nil a ||= 0 … Read more