equivalent of Python's "with" in Ruby
Ruby has syntactically lightweight support for literal anonymous procedures (called blocks in Ruby). Therefore, it doesn't need a new language feature for this.
So, what you normally do, is to write a method which takes a block of code, allocates the resource, executes the block of code in the context of that resource and then closes the resource.
Something like this:
def with(klass, *args) yield r = klass.open(*args)ensure r.closeend
You could use it like this:
with File, 'temp.txt', 'w' do |f| f.write 'hi' raise 'spitespite'end
However, this is a very procedural way to do this. Ruby is an object-oriented language, which means that the responsibility of properly executing a block of code in the context of a File
should belong to the File
class:
File.open 'temp.txt', 'w' do |f| f.write 'hi' raise 'spitespite'end
This could be implemented something like this:
def File.open(*args) f = new(*args) return f unless block_given? yield fensure f.close if block_given?end
This is a general pattern that is implemented by lots of classes in the Ruby core library, standard libraries and third-party libraries.
A more close correspondence to the generic Python context manager protocol would be:
def with(ctx) yield ctx.setupensure ctx.teardownendclass File def setup; self end alias_method :teardown, :closeendwith File.open('temp.txt', 'w') do |f| f.write 'hi' raise 'spitespite'end
Note that this is virtually indistinguishable from the Python example, but it didn't require the addition of new syntax to the language.
The equivalent in Ruby would be to pass a block to the File.open method.
File.open(...) do |file| #do stuff with fileend #file is closed
This is the idiom that Ruby uses and one that you should get comfortable with.
You could use Block Arguments to do this in Ruby:
class Object def with(obj) obj.__enter__ yield obj.__exit__ end end
Now, you could add __enter__
and __exit__
methods to another class and use it like this:
with GetSomeObject("somefile.text") do |foo| do_something_with(foo)end